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Variable temperature (−100 to −150°C) studies of the infrared spectra (3500–400 cm−1) of propenoyl bromide, CH2=CHCBrO, dissolved in liquid krypton, have been carried out. Utilizing six different conformer pairs, an enthalpy difference of 204 ± 20 cm−1 (2.44 ± 0.24 kJ/mol) was obtained, with the anti conformer (carbonyl bond trans to C=C bond) the more stable form. At ambient temperature, there is approximately 28 ± 2% of the syn conformer present. The anti conformer also remains in the infrared and Raman spectra of the polycrystalline solid. The optimal geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies, are reported for both conformers from MP2/6-31G(d) ab initio calculations. The potential function governing the conformational interchange has been obtained from the MP2/6-31G(d) ab initio calculations. The conformational stabilities were calculated from a variety of basis sets and at the highest level of calculations, MP2/6-311 + (2df,2pd), the anti conformer is predicted to be more stable by 178 cm−1, which is in excellent agreement with the experimental results. The r0 adjusted structural parameters have been obtained for propenoyl fluoride and chloride from a combination of the previously reported microwave rotational constants and ab initio predicted parameters. Several of the parameters for the chloride are significantly different than those proposed from an electron diffraction investigation. The results of these spectroscopic, structural, and theoretical studies are discussed and compared to the corresponding results for some similar molecules.

Variable temperature (−55 to −150 °C) studies of the infrared spectra (3500–60 cm −1 ) of allyl amine (3-aminopropene), CH 2 CHCH 2 NH 2 , dissolved in liquid krypton and/or liquid xenon have been carried out. From these data it has been possible to identify four of the possible five stable conformers as well as to determine their relative stabilities. The order of the conformers stabilities has been determined to be where the first indicator is for the relative position of the amino group (C= cis or G= gauche ) to the double bond (rotation around the C–C bond) and the second one (t= trans , g= gauche , g′= gauche ′) is the relative position of the amino rotor, i.e. rotation around the C–N bond: Ct, Gt≈Gg, Cg, and Gg′. The enthalpy differences have been determined between the most stable Ct conformer and the second most stable rotamer, Gt, to be 92±8 cm −1 (1.10±0.10 kJ/mol), and the third most stable rotamer, Gg, to be 122±12 cm −1 (1.46±0.14 kJ/mol) with the Cg having a significant larger value of 173±12 cm −1 (2.07±0.14 kJ/mol) than either of these forms. No evidence was obtained for the fifth conformer Gg′ which is predicted by most of the ab initio calculations to be less stable by more than 600 cm −1 than the Ct form. The percentage of each conformer at ambient temperature is estimated to be: Ct (23%), Gt (29%), Gg (25%) and Cg (20%). Utilization of diffuse functions for the ab initio calculations gives a distinctive preference for the gauche conformer for both the amino torsion and the relative position of the NH 2 group to the double bond. Therefore it is not possible to predict the conformer stability order from the ab initio calculations. The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for all of the conformers from MP2(full)/6-31G(d) ab initio calculations. The optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing several different basis sets up to MP2(full)/6-311+G(2df,2pd) and from density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants for six isotopomers of the Ct conformer and one isotopomer for the Gt, Gg and Cg forms along with ab initio predicted structural values, r 0 parameters have been obtained for all four observed conformers. The results are discussed and compared to the corresponding properties of some similar molecules.

Variable temperature (−110 to −150 °C) studies of the infrared spectra between 4000 and 50 cm−1 of ethylmethylamine, CH3CH2N(H)CH3, dissolved in liquid krypton have been recorded. Additionally, the infrared spectrum (4000–50 cm−1) of the solid has been recorded. All three possible conformers, i.e. N-methyl group (Me-trans, or T), hydrogen atom (H-trans, or G′), and lone pair (LP-trans, or G) trans to the methyl group of the ethyl moiety, have been identified with only the Me-trans conformer remaining in the solid. From the variable temperature studies the enthalpy difference has been determined to be 335±35 cm−1 (4.01±0.42 kJ/mol) between the most stable Me-trans conformer and the least stable LP-trans rotamer. An enthalpy difference of 177±27 cm−1 (2.12±0.32 kJ/mol) is estimated between the H-trans form and the most stable Me-trans conformer. These results are somewhat lower but still in reasonable agreement with the ab initio predictions at all levels of calculations. It is estimated that there is only 12±2% of the LP-trans form and 26±3% of the H-trans conformer present at ambient temperature. A complete vibration assignment is proposed for the Me-trans conformer which is supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. The conformational stabilities, barriers to internal rotation and inversion, and fundamental vibrational frequencies which have been determined experimentally are compared to those obtained from ab initio calculations. Utilizing previously reported microwave rotational constants for two isotopomers of the Me-trans rotamer along with ab initio predicted structural values, r0 adjusted parameters have been obtained for this conformer. The results are discussed and compare to the corresponding properties of some similar molecules.

The infrared spectra of gaseous and solid and the Raman spectrum (3200–400 cm −1 ) of liquid 1-chloroethylsilane (CH 3 CHClSiH 3 ) have been recorded. The SiH 3 torsional mode has been observed as sum and difference bands with the siliconhydrogen stretching vibrations at 2194 and 2159 cm −1 where the four determined values only vary by 3 cm −1 . Utilizing a torsional fundamental frequency of 152 cm −1 for the silyl rotor the three-fold periodic barrier of 934 cm −1 (2.67 kcal/mol) has been obtained. Estimates are also made for the methyl torsional barrier which is 1348 cm −1 (3.96 kcal/mol) from a frequency in the spectrum of the solid. The predicted barriers of 901 and 1483 cm −1 for the silyl and methyl rotors, respectively, have been obtained from the MP2/6-31G(d) calculations which agree well with the experimental values. A complete vibrational assignment is proposed which is based on infrared band contours, infrared intensities, Raman activities, and group frequencies and is consistent with the predicted frequencies utilizing the force constants from ab initio MP2/6-31G(d) calculations. Complete equilibrium geometries have been determined by ab initio calculations employing the 6-31G(d) and 6-311+G(d,p) basis sets with full electron correlation at the level of Moller–Plesset by the perturbation method to the second order (MP2). The results are discussed and compared to the corresponding values for some similar molecules.

The infrared spectra of ethyl bromosilane, CH 3 CH 2 SiH 2 Br and the Si-d 2 isotopomer, were recorded in the vapor, amorphous and the crystalline solid phases in the range 4000–400 cm −1 . The mid-infrared spectra of the ‘light’ compound, isolated at 4.8 K in the argon and the nitrogen matrices were also observed. Raman spectra of the liquids were recorded at various temperatures between 298 and 218 K, and the spectrum of the crystal was obtained from a sample sealed in a capillary at 210 K. Additional spectra of the amorphous and annealed crystals, which were deposited on a copper finger cooled with liquid nitrogen, were recorded. These vibrational spectra show that two conformers— anti and gauche —are present in the vapor and in the liquid, but only the gauche conformer remains in the crystalline solid. Six conformer pairs in the liquid phase were used to obtain the enthalpy difference which gave an average of 140±25 cm −1 (1.67±0.3 kJ/mol) with gauche form lower in energy. Additionally variable temperature (−120 to −155 °C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out and the enthalpy difference has been determined to be 130±13 cm −1 (1.56±0.16 kJ/mol), again with the gauche conformer the more stable form. At ambient temperature it is estimated that there is 22±2% of the anti conformer present. The optimized geometries, infrared and Raman intensities, and scaled vibrational frequencies for the anti and gauche conformers were obtained from ab initio MP2/6-31G(d) calculations. The conformational energy difference was also obtained from ab initio MP2/6-311+G(d, p) calculations which gave a predicted energy difference of 129 cm −1 with the gauche form the lowest energy. From the isolated Si–H stretch frequencies from the Si-d 1 isotopomer the Si–H distances were determined to be 1.481 and 1.480 A for the gauche and anti conformers, respectively. The spectroscopic and theoretical results are discussed and compared to the corresponding quantities for some similar molecules.

The infrared spectra (3500–50 cm −1 ) of the gas and solid and the Raman spectra (3500–50 cm −1 ) of the liquid and solid have been recorded for 2-hexyne, CH 3 –CC–CH 2 CH 2 CH 3 . Variable temperature studies of the infrared spectrum (3500–400 cm −1 ) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti / gauche conformer pairs, the anti ( trans ) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm −1 (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range −105 to −150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH 3 group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ζ , have been determined. The results are compared to similar properties of some corresponding molecules.

The Raman and infrared spectra of hydrazine, N2H4, and the deuteroisotopomer, N2D4, are compared to the predicted spectra from ab initio MP2(full)/6-31G(d) calculations with three scaling factors. Additionally, r0 structural parameters have been obtained by combining MP2(full)/6-311 + G(d,p) predicted values with previously determined rotational constants. Similar studies have also been initiated for three methyl substituted hydrazines, i.e. methylhydrazine (CH3NHNH2), 1,2-dimethylhydrazine (CH3NHNHCH3), and 1,1-dimethylhydrazine ((CH3)2NNH2). The results are discussed and compared to the corresponding values for some similar amines.

The infrared (3400– 50 cm 21 ) and/or Raman (3400 –10 cm 21 ) spectra of gaseous, xenon solution, liquid and solid 5chloropent-2-yne, CH2ClCH2CCCH3, have been recorded. These data indicate that the molecule exists in the anti (the C –Cl bond is trans to the CxC bond) and the gauche conformations in the vapor and liquid but only the anti conformer remains in the solid state. From a variable temperature infrared study of the xenon solution, the anti conformation has been determined to be more stable than the gauche form by 233 ^ 23 cm 21 (2.79 ^ 0.28 kJ/mol) and it is estimated that 39% of the sample is in the gauche form at ambient temperature. The optimized geometries, conformation stabilities, harmonic force fields, Raman activities, depolarization ratios, and infrared intensities have been obtained from ab initio MP2/6-31G(d) calculations with full electron correlation. These predicted quantities are compared to the corresponding experimental quantities when appropriate. Equilibrium geometries and energies for both conformers have been obtained from ab initio MP2/6-311G(d,p), MP2/6311G(2d,2p) and MP2/6-311G(2df,2pd) calculations. Vibrational assignments for the 24 normal modes for the anti conformer are proposed and several of the fundamentals for the gauche conformer are assigned. The sub-band structure on the pseudodegenerate vibrations of the methyl group indicates that it is almost free internal rotation. From this fine structure, the Coriolis coupling constants, j, have been determined. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules. q 2002 Elsevier Science B.V. All rights reserved.

The Raman spectra (3200-30 cm(-1)) of liquid and solid, and infrared spectra of gaseous and solid chloromethyl silyl dichloride, ClCH2SiHCl2, have been recorded. Variable temperature (-105 to -150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference was determined to be 363 +/- 40 cm(-1) (4.34 +/- 0.48 kJ mol(-1)), with the more stable form being the gauche conformer, which is consistent with the prediction from ab initio calculations at both the Hartree-Fock level and with full electron correlation by the perturbation method to second order. It is estimated that 92% of the sample is in the gauche form at ambient temperature. A complete vibrational assignment is proposed for the gauche conformer and several of fundamentals of the trans conformer based on infrared band contours, relative intensities, depolarization values, and group frequencies, which is supported by normal coordinate calculations utilizing the force constants from the ab initio MP2/6-31G(d) calculations. The r0 SiH bond distances of 1.476 and 1.472 A have been obtained for the trans and gauche conformers, respectively, from the silicon-hydrogen stretching frequencies. The optimized geometries have also been obtained from ab initio calculations utilizing several different basis sets with full electron correlation by the perturbation method up to MP2/6-311 + G(2d,2p). The results are discussed and compared to some corresponding results for several related molecules.

The infrared spectra (3200 to 50 cm−1) of gaseous and solid and Raman spectra (3200 to 10 cm−1) of the liquid and solid N-methylpropargyl amine (4-aza-1-pentyne), HCCCH2N(CH3)H, have been recorded. All three possible conformers, i.e., methyl group (Me-trans) hydrogen atom (H-trans), and lone pair (LP-trans) trans to the ethynyl group, have been identified in the fluid phase with only the conformer with the LP-trans remaining in the solid. Variable temperature (−105 to −150 °C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy difference has been determined to be 360 ± 72 cm−1 (4.31 ± 0.86 kJ mol−1), between the most stable LP-trans conformer and the second most stable Me-trans rotamer. An enthalpy difference of 100 ± 20 cm−1 is estimated between the Me-trans form and the least stable H-trans conformer. These results are in reasonable agreement with the ab initio predictions at all levels of calculations. It is estimated that there is only 8% of the H-trans form and 14% of the Me-trans conformer present at ambient temperature. A complete vibration assignment is proposed for the LP-trans conformer which is based on infrared band contours, infrared intensities, Raman activities, and group frequencies, which is supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) and DFT(B3LYP) calculations. Proposed assignments are also made for several of the fundamentals of the other two conformers. The conformational stabilities, barriers to internal rotation, and fundamental vibrational frequencies which have been determined experimentally are compared to those obtained from ab initio calculations. Utilizing previously reported microwave rotational constants for two isotopomers of the LP-trans rotamer along with ab initio predicted structural values, r0 parameters have been obtained for this conformer. The results are discussed and compare to the corresponding properties of some similar molecules.

Variable-temperature (−55 to −100 °C) studies of the infrared spectra (3500−400 cm-1) of methylhydrazine, CH3NHNH2, dissolved in liquid xenon have been recorded. From these data the enthalpy difference has been determined to be 323 ± 30 cm-1 (3.86 ± 0.36 kJ/mol) with the inner conformer (methyl group staggered and between the two hydrogens of the NH2 group) the more stable rotamer. A complete vibrational assignment is presented for the inner conformer, and several of the fundamentals of the outer conformer have been assigned. These assignments are consistent with the predicted wavenumbers obtained from ab initio MP2/6-31G(d) calculations utilizing three scaling factors. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. Hybrid density functional theory (DFT) calculations to obtain the structural parameters and conformational stability ...

The Raman spectra (3200 to 30 cm−1) of liquid and solid and the infrared spectra of gaseous and solid chloromethylsilyl bromide, ClCH2SiH2Br, were recorded. Utilizing three conformer pairs from the Raman spectrum of the liquid along with their ab initio predicted activities, the enthalpy difference of 216 ± 22 cm−1 (2.58 ± 0.26 kJ mol−1) was obtained with the trans conformer the more stable form. Variable temperature (−105 to 150° C) studies of the infrared spectra of the sample dissolved in liquid krypton were carried out and from these data, the enthalpy difference was estimated to be 250 ± 50 cm−1 (2.99 ± 0.60 kJ mol−1), again with the more stable form being the trans conformer. These values are consistent with the prediction from ab initio calculations both at the Hartree–Fock level and with full electron correlation by the perturbation method to second order. It is estimated that 37 ± 6% of the sample is in the gauche form at ambient temperature. Only the trans conformer remains in the spectra of the solid. A complete vibrational assignment is proposed for the trans conformer and also several of fundamentals of the gauche conformer based on infrared band contours, relative intensities, depolarization values and group frequencies, which is supported by normal coordinate calculations utilizing the force constants from the ab initio MP2/6–31G(d) calculations. The optimized geometries and conformational stabilities were also been obtained from ab initio calculations utilizing two additional basis sets with full electron correlation by the perturbation method. Estimates were made of the r0 structural parameters based on the predicted structural parameters from ab initio MP2/6–311 + G(d,p) calculations. The results are discussed and compared with some corresponding results for some related molecules. Copyright © 2002 John Wiley & Sons, Ltd.

The infrared spectra (3200-300 cm(-1)) of the gas and solid and the Raman spectra (3200-30 cm(-1) of the liquid with quantitative depolarization values and the solid have been recorded of ethynylmethyl cyclobutane (cyclobutylmethyl acetylene), c-C4H7CH2C[ triple bond]CH. Both the equatorial and the axial conformers have been identified in the fluid phases and both the gauche and trans conformations of the methyl acetylenic group have been identified for each ring conformer. Variable temperature (-105 to -150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy differences have been determined to the 112 +/- 11 cm(-1) (1.34 +/- 0.13 kJ mol) between the most stable equatorial-trans (Et) conformer and the equatorial-gauche (Eg) conformer which is the second most stable conformer and 327 +/- 35 cm(-1) (3.91 + 0.42 kJ/mol) with the axial-gauche (Ag) conformer which is the least stable conformer. The enthalpy difference between the axial-trans (At) and the equatorial-gauche(Eg) is 56 +/- 6 cm(-1). At ambient temperature there is approximately 33% of the Et conformer, 38% of the Eg form, 15% of the At and 14% of the Ag conformer. For the polycrystalline solid the Eg conformer is the only form present which probably results form the packing in the crystal. A complete vibrational assignment is proposed for both equatorial conformers and additionally a few of the fundamentals of the At and Ag conformers have been assigned. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. Complete equilibrium geometries have been determined for all four possible rotamers by ab initio calculations employing the 6-31G(d) and 6-311 + + G(d,p) basis sets at levels of restricted Hartree-Fock (RHF) and /or Moller-Plesset (MP2) with full electron correlation by the perturbation method to second order. The results are discussed and compared to those obtained for some similar molecules.

The far-infrared spectra (350–35 cm−1) of gaseous ethyl methyl ether-d 0 and ethyl methyl-d 3-ether have been recorded at a resolution of 0.10 cm−1. For the d 0 species, the fundamental asymmetric torsion of the more stable trans conformer (two methyl moieties are trans to one another) has been observed at 115.40 cm−1 with four upper state transitions falling to lower frequency, whereas, for the gauche form, it has been observed at 93.56 cm−1 with two excited states falling to lower frequency. the corresponding series for the d 3 species start from 106.00 and 87.10 cm−1, respectively. From these data, the asymmetric torsional potential coefficients for the d 0 species have been determined to be: V 1 = 572 ± 30; V 2 = 85 ± 8; V 3 = 619 ± 30; V 4 = 175 ± 18, and V 6 = −28 ± 3 cm−1. The trans to gauche and gauche to gauche barriers were calculated to be 958 cm−1 (11.5 kJ/mol) and 631 cm−1 (7.55 kJ/mol), respectively, with an energy difference of 550 ± 6 cm−1 (6.58 ± 0.07 kJ/mol). Utilizing three conformer pairs, variable temperature studies (−105 to −150°C) of the infrared spectra of the d 0 sample dissolved in liquid krypton gave an enthalpy difference of 547 ± 28 cm−1 (6.54 ± 0.33 kJ/mol) with the trans conformer the more stable rotamer. It is estimated that there is only 4% of the gauche conformer present at ambient temperatures. The structural parameters, conformational stabilities, barriers to internal rotation, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio gradient predictions from RHF/6-31G* and with full electron correlation at the MP2 level with three different basis sets. The adjusted r 0 structural parameters have been obtained for the trans conformer from combined ab initio MP2/6-311+G** predictions and previously reported microwave rotational constants. The reported distances should be accurate to 0.003 A and the angles to 0.5°. These results are compared to the corresponding quantities obtained for some similar molecules.

FT-microwave spectroscopy was carried out where the trans conformer was identified to be the most stable conformer. Variable temperature (-60 to -100 degrees C) studies of the Raman spectra (4000-50 cm(-1)) of ethylamine, CH3CH2NH2 dissolved in liquefied xenon have been carried out. From these data both conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 62 +/- 6 cm(-1) (0.746 +/- 0.072 kJ mol(-1)) with the trans conformer the more stable form. The percentage of the gauche conformer is estimated to be 60% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations with the Moller-Plesset perturbation method to the second order (MP2(full)) and the fourth order (MP4(SDTQ)) as well as with density functional theory by the B3LYP method by utilizing a variety of basis sets. Vibrational assignments have been made for the observed bands which have been predicted by MP2(full)/6-31G(d) ab initio calculations which includes harmonic force fields, frequencies, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some similar molecule. (C) 2014 Published by Elsevier B.V.

The infrared spectra (3200–50 cm −1 ) of gaseous and solid and Raman spectra (3200–10 cm −1 ) of the liquid with qualitative depolarization ratios and solid 3-bromo-3,3-difluoropropene CH 2 CHCBrF 2 have been recorded. Both the gauche and cis conformers have been identified in the fluid phase, but the gauche conformer is thermodynamically more stable than the cis rotamer and it is the only rotamer present in the spectrum of the annealed solid. Variable temperature (−105 to −150°C) studies of the infrared spectra of the sample dissolved in liquid krypton has been carried out. From these data, the enthalpy difference has been determined to be 281±28 cm −1 (3.36±0.33 kJ mol −1 ), with the gauche conformer as the more stable rotamer, which is in agreement with the ab initio predictions at all levels of calculations. It is estimated that there is only 11% of the cis conformer present at an ambient temperature. A complete vibration assignment is proposed for the gauche conformer which is based on infrared band contours, depolarization values, and group frequencies which is supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G (d) calculations. The conformational stabilities, barriers to internal rotation, and fundamental vibrational frequencies which have been determined experimentally are compared to those obtained from the ab initio calculations. The results are discussed and compared with the corresponding properties of some similar molecules.

Variable temperature (−105 to −150°C) studies of the infrared spectra (3500–400 cm −1 ) of (methylthio)dichlorophosphine, CH 3 SPCl 2 , dissolved in liquid krypton have been carried out. Utilizing the conformer bands at 518, 511and 1319 cm −1 ( gauche ) and 1311 cm −1 ( trans ), an enthalpy difference of 306±25 cm −1 (3.66±0.30 kJ/mol) was obtained with the trans conformer, the more stable form. The trans conformer also remains in the infrared and Raman spectra of the polycrystalline solid. At ambient temperature, there is approximately 72% of the trans conformer present. The optimal geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies are reported for both conformers from ab initio calculations. These calculations were carried out at the restricted Hartree–Fock (RHF) level and/or with electron correlation to second order (MP2), utilizing the basis sets 6-31G(d), 6-311+G(d,p) and 6-311+G(2d,2p). At the highest level of calculations, MP2/6-311+(2d,2p), the trans conformer is predicted to be more stable by 587 cm −1 , which is in reasonable agreement with the experimental results. The coefficients from the potential function governing the conformational interchange have been obtained from the MP2/6-31G(d) ab initio calculations. The other calculated quantities are compared with the experimentally determined values where applicable, as well as some corresponding results for some similar molecules.

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500–400 cm −1 ) of 1-chloropropane (CH 3 CH 2 CH 2 Cl) and 1-bromopropane (CH 3 CH 2 CH 2 Br) dissolved in liquid krypton and xenon, respectively, have been recorded. Utilizing two conformer pairs in krypton solution for chloride and three conformer pairs in xenon solution for bromide, enthalpy differences of 52±3 cm −1 (0.62±0.06 kJ/mol) and 72±7 cm −1 (0.86±0.08 kJ/mol) were obtained for the chloride and bromide, respectively, with the gauche form being the more stable conformer for both molecules. From these data, it is estimated that 28 and 26% of trans form are present at ambient temperature for the chloride and bromide, respectively. The conformation stabilities, harmonic force constants, fundamental frequencies, infrared intensities and Raman activities have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations for both halopropanes and these quantities have been compared to the experimental values when appropriate. The optimized geometries have also been obtained with several different ab initio basis sets with full electron correlation by the perturbation method up to MP2/6-311+G(2d,2p). The r 0 structural parameters of both halopropanes have been obtained by combining the ab initio data with the previously reported microwave rotational constants for both conformers. The quantities are compared to the corresponding results for some similar molecules.

The infrared spectra (3500–400 cm −1 ) of rare gas solutions of chloromethyl thiirane (3-chloropropylene sulfide), c -SC 2 H 3 CH 2 Cl, at variable temperatures (−55 to −150°C), have been recorded and only the gauche -2 and gauche -1 conformers are present in detectable amounts at ambient temperature. Utilizing six conformer pairs in the xenon solution, an enthalpy difference of 105±15 cm −1 (1.26±0.18 kJ mol −1 ) has been obtained with the gauche -2 conformer, the more stable form. From these data, it is estimated that 38% of the gauche -1 form is present at ambient temperature. Complete vibrational assignments are provided for both stable conformers. The conformational stabilities, harmonic force constants, fundamental frequencies, infrared intensities, and Raman activities have been obtained from MP2/6-31G(d) calculations with full electron correlation. These quantities have been compared to the experimental values when appropriate. The optimized geometries have also been obtained with several different ab initio basis sets with full electron correlation up to MP2/6-311+G(2d,2p). The adjusted- r 0 structural parameters have been obtained for the gauche -1 conformer by combining the ab initio data with the previously reported microwave rotational constants. The predicted structural parameters for both conformers are compared to those reported from an electron diffraction study. These results are compared to the corresponding quantities of some similar molecules.

The infrared and Raman spectrum of 1-bromo-3-fluoropropane is reported in the gas, liquid, amorphous solid and annealed polycrystalline states. Only one of the five possible conformers is stable in the crystal, designated the C conformer. The disordered phases show the presence of several other conformers of higher energy, due entirely to conformers designated B and D. Ab initio calculations were performed as rhf/4-31g*/MIDI-4*, rhf/6-31g* and mp2/6-31g* (both frozen core and full electron correlation) for all five conformers. The scaled harmonic force field obtained using the mp2 = full/6-31g* level of the theory is reported for the most stable conformer together with an assignment of fundamentals and potential energy distributions for local symmetry coordinates. Selected computational results are reported for all conformers together with scaled and unscaled wavenumbers and infrared and Raman intensities. The temperature dependent Raman spectrum is reported from room temperature to -100 degrees C. Only three of the five possible conformers can be identified in this spectrum, and there is no evidence of the other two. The energy differences between conformers in the liquid phase were found experimentally to be 132+/-27, 232+/-46 and 106+/-30 cm(-1), respectively between the D and C, B and C and D and B conformers. These differences are substantially less than the differences calculated ab initio at the highest level of the theory used, suggesting that energy differences were decreased by large dipole-dipole interactions present in the liquid but not in the gas.

Infrared spectra of 2-chloroethyl trifluorosilane (CETFS) (ClCH2CH2SiF3) were obtained in the vapour, amorphous and crystalline solid phases in the range 4000–50 cm−1. Additional variable temperature spectra in liquefied xenon and spectra in argon and nitrogen matrices at 5 K were recorded. Raman spectra of the compound as a liquid were recorded at various temperatures between 298 and 180 K and amorphous and crystalline solids were obtained. The spectra of CETFS revealed the existence of two conformers (anti and gauche) in the vapour and in the liquid. Large variations in the infrared and Raman spectra were observed when the vapour was shock-frozen on a window at 80 K and subsequently annealed. An intermediate phase appeared at ca. 125 K containing both conformers. A crystal was formed at 160 K, and ca. 18 infrared and/or Raman bands present both in the fluid phases and in the 125 K solid vanished in this crystal. From the intensity variations between 293 and 183 K of four Raman band pairs, Δ H 0 (anti−gauche)=0.8±0.3 kJ mol −1 was obtained in the liquid. In liquid xenon under pressure a ΔH value of −0.7±0.1 kJ mol−1 was calculated from the intensity variations between 218 and 173 K of two band pairs in the infrared spectra. Annealing experiments indicate that the anti conformer has slightly lower energy in argon and nitrogen matrices. Also, the anti conformer has the lower energy in liquid xenon, whereas the more polar gauche rotamer is the low energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted in detail. Ab initio calculations were performed using the gaussian 94 program with the HF/6-311G∗ basis set and gave optimized geometries, infrared and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy difference derived was 3.8 kJ mol−1 with anti being the low energy conformer.

In our previous studies, a rule was formulated referring to how the internuclear distances and the bond angles in a second conformer differ from those in the most stable one. A test of this rule on 36 molecules (existing as two conformer mixtures) showed that it works well for the internuclear distances but is poor in predicting the bond angle changes. We undertook a systematic analysis of some of the molecules showing the highest angular changes using ab initio methods. It was found that the X–C–Y bond angles in systems like CH2X–YH, where Y=O, S and CH2X–YH2, where Y=N, P (X=CH3, F, Cl) can differ as much as 5.8° in different conformers and the direction of change mostly contradicts the above mentioned rule.

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500–400 cm −1 ) of (chloromethyl)phosphonothioic difluoride (ClCH 2 P(S)F 2 ) dissolved in liquid xenon and krypton have been recorded. From these data, the enthalpy difference has been determined to be 244±16 cm −1 (2.92±0.19 kJ mol −1 ) with the trans conformer being the more stable rotamer. Complete vibrational assignments are presented for both conformers, which are consistent with the predicted wavenumbers obtained from ab initio MP2/6-31G(d) calculations utilizing two scaling factors. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. Hybrid density function theory (DFT) calculations to obtain the structural parameters and conformational stability by the B3LYP/6-31G(d) method were also carried out. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules. The r 0 structural parameters have been obtained from a combination of the previously reported microwave rotational constants and ab initio MP2/6-311+G(d,p) predicted parameters. The results are compared to some corresponding quantities for some similar molecules.

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500–400 cm −1 ) of methyl vinyl difluorosilane, CH 2 CHSiF 2 CH 3 , dissolved in liquid xenon and krypton have been recorded. Utilizing three sets of conformer doublets due to the cis and gauche rotamers from the krypton solution and two pairs from the xenon solution, the enthalpy difference has been determined to be 67±7 cm −1 (0.80±0.09 kJ/mol) and 83±11 cm −1 (0.99±0.14 kJ/mol), respectively, with the gauche conformer the more stable form. However, in the crystalline solid only the cis conformer is present. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G(2d,2p) with full electron correlation by the perturbation method from which the conformational stabilities have been determined. With the largest basis set MP2/6-311+G(2d,2p), the cis conformer is predicted to be the more stable conformer by 10 cm −1 which is inconsistent with the experimental results; however, this value is so small that the ab initio prediction cannot be relied on to give the correct conformer stability. The spectroscopic and theoretical results are compared to the corresponding quantities for some similar molecules.

The infrared (3500–40 cm−1) spectra of gaseous, liquid and solid 3-methyl-3-butene nitrile, CH2C(CH3)CH2CN, and trans 3-pentenenitrile, CH3CHCHCH2CN, have been recorded. Both the cis and gauche conformers have been identified for both conformers in the fluid phases but only the cis form remains in the solid. Variable temperature (−55 to −100°C) studies of the infrared spectra of the samples dissolved in liquid xenon have been carried out. From these data, the enthalpy difference has been determined to be 174±20 cm −1 (2.08±0.24 kJ/mol ) for 3-methyl-3-butene nitrile with the cis conformer the more stable rotamer and 187±20 cm −1 (2.23±0.24 kJ/mol ) for trans 3-pentenenitrile, again with the cis rotamer the more stable form. Complete equilibrium geometries have been obtained for both rotamers for both molecules by ab initio calculations employing the 6-31G(d), 6-311G(d,p), 6-311+G(d,p) and 6-311+G(2d,2p) basis sets at the levels of restricted Hartree–Fock and/or Moller–Plesset to second order. Only the MP2/6-311+G(2d,2p) calculation gives the correct conformer stability for 3-methyl-3-butene nitrile.

Variable temperature (−105 to −150°C) studies of the infrared spectra (3500–400 cm−1) of methylvinyldifluorosilane, CH2CHSiF2CH3, dimethylvinylfluorosilane CH2CHSiF(CH3)2 and methylvinyldichlorosilane, CH2CHSiCl2CH3, dissolved in liquid krypton have been recorded. The enthalpy difference of methylvinyldifluorosilane has been determined to be 53±11 cm −1 (0.64±0.13 kJ/mol ) with the gauche conformer the more stable form. However in the crystalline solid only the cis conformer is present. For the corresponding dichlorosilane the enthalpy difference has been determined to be 46±20 cm −1 (0.55±0.24 kJ/mol ) with the cis conformer more stable. For dimethylvinylfluorosilane the enthalpy difference has been determined to be 32±7 cm −1 (0.38±0.08 kJ/mol ) with the gauche conformer the more stable form. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G(2d,2p) with full electron correlation by the perturbation method for all three of the silanes from which the conformational stabilities have been determined.

The infrared (IR) spectra of dichloromethylmethyl dichlorosilane (Cl2CHCH3SiCl2) were recorded in the vapor, amorphous and partly crystalline phases between 4000 and 50 cm−1. IR spectra (4000–450 cm−1) of the compound were also obtained when isolated in argon, nitrogen and krypton matrices at 4.8 K before and after annealing to temperatures in the range 15–50 K. Raman spectra of the liquid were recorded at various temperatures between 295 and 147 K. Spectra of the amorphous and annealed crystal deposited on a copper finger at 78 K were obtained. The spectra showed the existence of two conformers — anti and gauche — in the vapor and in the liquid. Approximately 12 IR bands were reduced in intensity and 6 Raman bands present in the fluid phases vanished upon crystallization. From the intensity variations of two band pairs with temperature, a ΔH0 value of 0.4±0.3 kJ mol−1 between the conformers was obtained in the liquid, anti being the low-energy conformer. Small increases and decreases in the IR band intensities were observed in the matrix spectra after annealing to 32 (nitrogen), 36 (argon) and 50 K (krypton). The enthalpy difference between the conformers is low in the matrices, but the anti conformer had lower energy than the gauche. Ab initio calculations were performed using the Gaussian -94 program with the RHF/6-311G∗ basis function and gave optimized geometries, IR and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy derived was 4.4 kJ mol−1 with anti being the low-energy conformer. The dipole moments were calculated to be 1.2 and 3.1 debye for the anti and gauche conformers, respectively. Correlation between the observed and calculated wavenumbers of both conformers revealed that anti was present in the crystal, and complete assignments of the spectra have been carried out.

The infrared spectra (3500–50 cm −1 ) of the gas and solid and the Raman spectra (3500–50 cm −1 ) of the liquid and solid have been recorded for 1-fluoro-2-butyne, CH 3 CCCH 2 F. Equilibrium geometries and energies have been determined by ab initio and hybrid DFT methods using a number of basis sets. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on vibrational–rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH 3 group exhibits almost completely free rotation which is in agreement with the observation of Coriolis sub-band structure in two of the degenerate methyl vibrations. The results are compared to the corresponding quantities for some similar molecules.

The far-infrared spectrum of gaseous 3-fluoro-1-butene, CH2CHC(CH3)FH, has been recorded at a resolution of 0.10 cm-1. The asymmetric torsional fundamentals of the most stable form HE (hydrogen ato...

The Raman (3500–40 cm−1) and infrared (3500–70 cm−1) spectra of gaseous and solid 2-methoxypropene, CH3O(CH3)C=CH2, and the isotopomers, CD3O(CH3)C=CH2 and CH3O(CD3)C=CD2 have been recorded. In addition, the Raman spectra of the liquids have been recorded with qualitative depolarization measurements. All of these data indicate that only one conformer is present in the fluid phases at ambient temperature and this form is the cis conformer, which remains in the solid. Assignments are provided for the fundamentals of all three isotopomers for the cis conformer with Cs symmetry. The far-infrared spectra of all three isotopic species have been recorded at a resolution of 0.1 cm−1 in the gas and 1.0 cm−1 in the solid. The parameters of the potential function governing the asymmetric torsion are determined to be V3 = 1485 ± 9 cm−1 and V6 = −55 ± 4 cm−1 for the d0 compound, where only two terms were determined, since a second conformer was not evident. The barrier to internal rotation for the methyl group attached to the oxygen atom is 1370 ± 8 cm−1 and the C—CH3 barrier is 772 ± 5 cm−1. Ab initio calculations with full electron correlation have been carried out by the perturbation method to second order to obtain the equilibrium structural parameters, harmonic force constants, fundamental frequencies, infrared intensities, Raman activities, depolarization values, and conformational stability. The predicted values have been compared to the experimental values where appropriate.

The Raman spectra (3200–30 cm−1) of liquid and solid, and infrared spectra of gaseous and solid chloromethyl silyl chloride, ClCH2SiH2Cl, have been recorded. Variable temperature (−105–−150°C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference is 177 ± 35 cm−1 (2.12 ± 0.42 kJ/mol), with the more stable form being the trans conformer, which is consistent with the prediction from ab initio calculations at both the Hartree–Fock level and with electron correlation by the perturbation method to second order. It is estimated that 56% of the sample is in the trans form at ambient temperature. A complete vibrational assignment is proposed for both the trans and gauche conformers based on infrared band contours, relative intensities, depolarization values, and group frequencies, which is supported by normal coordinate calculations utilizing the force constants from the ab initio MP2/6-31G(d) calculations. The optimized geometries have also been obtained from ab initio calculations utilizing several different basis sets with full electron correlation by the perturbation method up to MP2/6-311+G(2d,2p). The results are discussed and compared to some corresponding results for several related molecules.

The infrared spectra (3500–50 cm−1) of the gas and solid and the Raman spectra (3500–50 cm−1) of the liquid and solid were recorded for 5-fluoropent-2-yne, CH3–CC–CH2CH2F. Variable temperature studies of the infrared spectrum (3500–400 cm−1) of 5-fluoropent-2-yne dissolved in liquid krypton and xenon were also recorded. Utilizing anti–gauche conformer pairs, the enthalpy difference was determined as 272 ± 11 cm−1 (3.25 ± 0.13 kJ mol−1) and 297 ± 31 cm−1 (3.55 ± 0.37 kJ mol−1) from the xenon and krypton solutions, respectively, with the anti rotamer the more stable form. Equilibrium geometries and energies of the two conformers have been determined by ab initio and hybrid density functional theory (DFT) methods using a number of basis sets. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on vibrational–rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH3 group exhibits almost completely free rotation, which is in agreement with the observation of sub-band structure in the degenerate methyl vibrations from which values of the Coriolis coupling constant, ζ, were determined. The results are discussed and compared with the corresponding quantities for some similar molecules.

The Raman spectra (3400–10 cm−1) of liquid and solid and the infrared spectra (3400–50 cm−1) of gaseous, xenon solution and solid 4-chlorobut-1-yne, CH2ClCH2CCH, were recorded. These data indicate that the molecule exists in the anti (the C—Cl bond is trans to the CC bond) and the gauche conformations in the vapor and liquid and that both conformers persist in the solid with an indication that the gauche conformer may be more stable in this physical state. From a variable-temperature infrared study of the xenon solution, the anti conformation has been determined to be more stable than the gauche form by 147 ± 10 cm−1 (1.76 ± 0.12 kJ mol−1). From these data it is estimated that 50% of the sample is in the gauche form at ambient temperature. The optimized geometries, conformation stabilities, harmonic force fields, Raman activities, depolarization ratios and infrared intensities were obtained from MP2/6–31G(d) ab initio calculations with full electron correlation. These quantities were compared with the corresponding experimental quantities when appropriate. Equilibrium geometries and energies for both conformers were obtained from ab initio MP2/6–311 + G(d, p) and MP2/6–311 + G(2d, 2p) calculations. Vibrational assignments for the 24 normal modes for both the anti and gauche conformers are proposed. These experimental and theoretical results are compared with the corresponding quantities for some similar molecules. Copyright © 2001 John Wiley & Sons, Ltd.

The infrared spectra (3200–30 cm −1 ) of gaseous and solid ethyl fluorosilane, CH 3 CH 2 SiH 2 F, have been recorded. Additionally, the Raman spectra (3200–30 cm −1 ) of the liquid and solid have been recorded and quantitative depolarization values obtained. Both the gauche and trans conformers have been identified in the fluid phases but only the gauche conformer remains in the solid. Variable temperature (−105 to −150°C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference has been determined to be 54±16 cm −1 (646±191 J/mol) with the gauche conformer the more stable form. This is consistent with the predictions from ab initio, MP2/6-311+G(2d,2p), calculation as well as those with smaller basis sets with full electron correlations. A complete vibrational assignment is proposed for both the trans and gauche conformers based on infrared band contours, relative intensities, depolarization values, and group frequencies, which are supported by normal-coordinate calculations utilizing the force constants from MP2/6-31G(d) ab initio calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing a variety of basis sets up to 6-311+G(2d,2p) at levels of restricted Hartree–Fock (RHF) and/or Moller Plesset to the second order (MP2) with full electron correlation. The adjusted r 0 parameters have been obtained for both conformers from a combination of the previously reported rotational constants with ab initio predicted values. All results are compared to similar quantities of some corresponding molecules.

The infrared spectra (3500–50 cm−1) of the gas and solid and the Raman spectra (3500–50 cm−1) of the liquid and solid were recorded for butyronitrile (propyl cyanide), CH3CH2CH2CN. Both the anti (methyl group trans to the cyanide group) and gauche conformers were identified in the fluid phases. Variable temperature studies of the infrared spectrum (3500–400 cm−1) of the sample dissolved in liquid xenon (−60 to − 100°C) were recorded. Utilizing nine sets of conformer pairs, the enthalpy difference was determined as 40 ± 3 cm−1 (0.48 ± 0.04 kJ mol−1) with the gauche conformer the more stable form. At ambient temperature there is approximately 30% of the anti conformer present in the vapor state. Either the anti or gauche conformers could be obtained in the crystalline state depending on whether the solid was obtained from the liquid or from the gas sprayed on a cold substrate. A complete vibrational assignment is proposed for both conformers based on infrared contours, relative intensities, depolarization values and group frequencies which are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6–31G(d) calculations. Complete equilibrium geometries were determined for both rotamers by ab initio calculations employing the 6–31G(d), 6–311 + G(d,p) and 6–311 + G(2df,2pd) basis sets at the level of Moller–Plesset with full electron correlation by the perturbation method to the second order (MP2). From all of these calculations the gauche conformer is predicted to be the more stable form. The r0 adjusted structural parameters were obtained from a combination of the previously reported microwave rotational constants and ab initio predicted parameters. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.

The infrared (3500–40 cm −1 ) spectra of gaseous and solid dicyclopropyl methane, (c-C 3 H 5 ) 2 CH 2 , along with the Raman (3500–30 cm −1 ) spectra of the liquid and solid phases of this molecule have been recorded. Three of the four possible conformers have been identified in the fluid phases, and they are the gauche – gauche rotamer with C 2 symmetry, gauche – gauche rotamer with C s symmetry, and the gauche – cis rotamer with C 1 symmetry. Variable temperature (−55 to −145°C) studies of the infrared spectra of the sample dissolved in liquid xenon and krypton have been carried out. Utilizing six different combinations of pairs of bands from the C 2 and C s conformers, the average value of Δ H , the enthalpy difference between these two conformers, is 239±13 cm −1 (2.86±0.16 kJ/mol) from the xenon solution and 211±12 cm −1 (2.52±0.14 kJ/mol) from the krypton solution, with the C 2 form the more stable rotamer in both solvents. The enthalpy difference for the gauche – cis form was obtained from the temperature dependence of the relative intensities of three of the fundamentals of this conformer with three fundamentals of the C 2 form and two fundamentals of the C s form, from which a value of 479±84 cm −1 (5.73±1.00 kJ/mol) was obtained between the C 2 rotamer and this less stable C 1 form. A complete vibrational assignment is proposed for the C 2 conformer and most of the fundamentals have been assigned for the C s conformer, utilizing predictions of fundamental frequencies, infrared intensities, and Raman activities from MP2/6-31G(d) ab initio calculations. The structural parameters, dipole moments and conformational stabilities of the four possible conformers of dicyclopropyl methane have been obtained from RHF/6-31G(d), MP2/6-31G(d) and MP2/6-311+G(d,p) ab initio calculations, with the latter two incorporating full electron correlation. The predicted conformational stabilities are consistent with the experimental results. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

The infrared spectra (3200-50 cm−1) of gaseous and solid vinyltrichlorosilane, CH2=CH-SiCl3, have been recorded. In addition, the Raman spectrum (3200-10 cm−1) of the liquid has been recorded and quantitative depolarization values obtained. The infrared spectrum of the sample dissolved in liquid xenon (−80°C) has also been recorded. Using the experimental data and normal coordinate calculations with scaled ab initio force constants, the complete vibrational assignment is proposed. The torsional mode was observed in the infrared spectrum of the gas at 69 cm−1 and the threefold barrier of internal rotation was calculated to be 500 cm−1 (5.98 kJ/mol). Ab initio calculations have been carried out at the restricted Hartree–Fock level of the theory as well as with full electron correlation by the perturbation method to second order with different basis sets up to 6-311+G(d,p) to obtain the optimized geometries, harmonic force constants, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies. The ab initio predicted structural parameters are compared with those obtained from a previous electron diffraction study.

Variable temperature (−105 to −145°C) studies of the infrared spectra (3500–400 cm−1) of methylamine, CH3NH2, dissolved in liquid krypton have been recorded. From these data, the hydrogen bonding enthalpy has been determined to be 530 ± 29 cm−1 (6.34 ± 0.35 kJ/mol). The elusive ν13 and ν14 fundamentals, which are strongly mixed CH3 rock and NH2 twist, have been observed at 1244 and 876 cm−1, respectively. These assignments are supported by frequency predictions from ab initio MP2/6-31G(d) calculations where the predicted infrared intensities for these two vibrations are 0.054 and 0.002 km/mol. The ab initio predicted infrared spectrum compares very favorably with that observed in the krypton solution. Normal coordinate calculations have also been carried out for four other isotopomers of methylamine, CH3NHD, CH3ND2, CD3NH2, and CD3ND2 and vibrational assignments given from previously reported infrared spectra of matrix isolated samples. The Raman spectrum of these latter three isotopes, along with the normal species, have been predicted from MP2/6-31G(d) calculations and the results compared to the experimental spectra. The equilibrium structural parameters have been obtained from ab initio calculations utilizing several different basis sets with full electron correlation by the perturbation method to second order. These predicted values are compared to the previously reported experimental structural parameters.

Variable temperature studies of the infrared spectra (3500–400 cm −1 ) of 1-pentyne, CH 3 CH 2 CH 2 C CH, dissolved in liquid xenon (−55 to −100°C) and liquid krypton (−105 to −150°C) have been recorded. These data indicate that the anti (methyl group trans to the acetylenic group) and gauche conformers have relative concentrations that vary with the temperature, i.e. enthalpy nonzero. Utilizing seven sets of conformer pairs for the xenon solution and ten sets of conformer pairs for the krypton solution, the enthalpy difference has been determined to be 50±6 cm −1 (0.60±0.07 kJ/mol) and 45±4 cm −1 (0.54±0.05 kJ/mol) , respectively, with the anti conformer the more stable form. Because of two equivalent gauche forms, this conformer is estimated to be in higher abundance at 61±1% in the xenon solution and 62±1% in the krypton solution. Optimized geometries and conformational stabilities have been obtained from ab initio calculations with basis sets 6-31G(d), 6-311+G(d,p), 6-311+G(2d,2p) and 6-311+G(2df,2pd) with full electron correlation by the perturbation method to second order (MP2). All of the calculations predict the gauche rotamer to be the more stable form with a high value of 181 cm −1 from the MP2/6-311+G(d,p) calculations and a low value of 107 cm −1 from the MP2/6-311+G(2d,2p) calculation. The r o adjusted structural parameters have been obtained from a combination of the microwave rotational constants and ab initio predicted parameters. The values are compared to the recently reported values from an electron diffraction study where the value for the C C bond distance appears to be too long. The results are discussed and the conformational stability is compared to those obtained for some similar molecules.

The far infrared spectrum from 370 to 50 cm −1 of gaseous 2-bromoethanol, BrCH 2 CH 2 OH, was recorded at a resolution of 0.10 cm −1 . The fundamental O–H torsion of the more stable gauche ( Gg ′) conformer, where the capital G refers to internal rotation around the C–C bond and the lower case g to the internal rotation around the C–O bond, was observed as a series of Q-branch transitions beginning at 340 cm −1 . The corresponding O–H torsional modes were observed for two of the other high energy conformers, Tg (285 cm −1 ) and Tt (234 cm −1 ). The heavy atom asymmetric torsion (rotation around C–C bond) for the Gg ′ conformer has been observed at 140 cm −1 . Variable temperature (−63 to −100°C) studies of the infrared spectra (4000–400 cm −1 ) of the sample dissolved in liquid xenon have been recorded. From these data the enthalpy differences have been determined to be 411±40 cm −1 (4.92±0.48 kJ/mol) for the Gg ′/ Tt and 315±40 cm −1 (3.76±0.48 kJ/mol) for the Gg ′/ Tg , with the Gg ′ conformer the most stable form. Additionally, the infrared spectrum of the gas, and Raman spectrum of the liquid phase are reported. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental frequencies have been obtained from ab initio calculations utilizing different basis sets at the restricted Hartree–Fock or with full electron correlation by the perturbation method to second order. The theoretical results are compared to the experimental results when appropriate. Combining the ab initio calculations with the microwave rotational constants, r 0 adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg ′ conformers.

The infrared spectra (3400−300 cm-1) of gaseous, xenon and krypton solutions, and solid state and the Raman spectra (3400−10 cm-1) of the liquid and solid states have been recorded for 4-fluoro-1-butyne, CH2FCH2C⋮CH. These data have been interpreted to show that the molecule exists in the anti conformation (the C−F bond is trans to the C⋮C bond) and the gauche forms in the vapor and liquid, but only the gauche conformer is present in the solid. From variable-temperature infrared studies of xenon and krypton solutions, the anti conformation has been determined to be more stable than the gauche form by 215 ± 22 cm-1 (2.57 ± 0.26 kJ/mol) and 170 ± 17 cm-1 (2.04 ± 0.2 kJ/mol), respectively. The asymmetric torsional fundamentals have been observed at 109.4 and 116.6 cm-1 for the more stable anti and the high-energy gauche conformers, respectively. From these data the asymmetric torsional potential function governing the internal rotation about the C−CH2F bond has been determined and the potential parameters ar...

The Raman spectra (3500–20 cm−1) of liquid with depolarization values and solid, as well as the infrared spectra of the gas, the sample isolated in argon and nitrogen matrices at ca. 5 K and solid dimethyl vinyl fluorosilane, CH2 CHSi(CH3)2F, have been recorded. Both gauche and syn rotamers have been identified in the fluid phases but only the syn conformer remains in the solid. Variable temperature (−55 to −150°C) studies of the infrared spectra (4000 and 400 cm−1) of dimethyl vinyl fluorosilane dissolved in liquid xenon and krypton have been recorded. From the xenon and krypton data, the enthalpy differences have been determined to be 53±9 cm−1 (0.64±0.10 kJ/mol) and 44±7 cm−1 (0.53±0.09 kJ/mol), respectively, with the gauche conformer being the more stable form. The intensity variations with temperature of the Raman spectrum of the liquid gave an enthalpy difference of 25±15 cm−1 (0.30±0.18 kJ/mol) also with the gauche conformer being the more stable form. Vibrational assignments are provided for both conformers. Complete equilibrium geometries have been determined for both rotamers using ab initio calculations employing the 6-31G(d), 6-311+G(d,p) and 6-311+G(2d,2p) basis sets at the levels of restricted Hartree–Fock (RHF) and/or with full electron correlation by the perturbation method, Moller–Plesset (MP), to second order. The syn conformer is predicted to be the more stable conformer from all ab initio calculations except those of MP2/6-31(d) which predict the gauche form being the more stable conformer by 54 cm−1 (0.65 kJ/mol) although the values favoring the syn form are all very small. These results are compared to the corresponding quantities of some similar molecules.

The infrared (3500–30 cm −1 ) spectra of gaseous and solid and the Raman (3500–200 cm −1 ) spectra of the liquid with quantitative depolarization ratios and solid trans -3-chloropropenoyl chloride ( trans -ClCHCHCClO) have been recorded. These data indicate that both the anti (carbonyl bond trans to the carbon–carbon double bond) and syn conformers are present in the fluid states but only the anti conformer is present in the crystalline state. The mid-infrared spectra of the sample dissolved in liquid xenon as a function of temperature (−55 to −100°C) have been recorded. Utilizing conformer pairs at 870 and 725 cm −1 , 1215 and 1029 cm −1 , and 1215 and 1228 cm −1 , the enthalpy difference has been determined to be 136±5 cm −1 (389±14 cal mol −1 ) with the anti conformer the more stable form. Optimized geometries and conformational stabilities were obtained from ab initio calculations at the levels of RHF/6-31G(d), MP2/6-31G(d), MP2/6-311++G(d,p), MP2/6-311++G(2d,2p) and MP2/6-311++G(2df,2pd) with only the latter two calculations predicting the anti rotamer to be the more stable form. The vibrational frequencies, harmonic force constants and infrared intensities were obtained from the MP2/6-31G(d) calculations, whereas the Raman activities and depolarization values were obtained from the RHF/6-31G(d) calculations. The spectra are interpreted in detail and the results are compared with those obtained for some related molecules.

The far infrared spectra of 1-butene, CH 2 CHCH 2 CH 3 , and the d 3 species CH 2 CHCH 2 CD 3 have been recorded from 50 to 360 cm −1 at a resolution of 0.10 cm −1 . The geometrical structures and vibrational frequencies of the cis (synplanar) and gauche (anticlinal) conformers have been determined by ab initio calculations in order to calculate torsional constants and to aid in assignments of the far infrared bands. A wide range of basis sets and ab initio theoretical methods up to MP4 have been used in order to predict the cis – gauche conformational energy difference. The fundamental and a few other methyl torsional transitions have been observed for both the cis and gauche conformers for both isotopic species and threefold barriers to internal rotation of 1680±15 cm −1 (4.80±0.04 kcal / mol ) for the cis rotamer and 1150±50 cm −1 (3.29±0.14 kcal / mol ) for the gauche conformer have been determined. The methyl barrier for the cis conformer is much higher than that derived from the microwave splittings. The potential energy function for asymmetric torsion has been redetermined from which values of the cis to gauche barrier of 835±48 cm −1 (2.39±0.14 kcal / mol ), and the gauche to gauche barrier of 615±51 cm −1 (1.76±0.15 kcal / mol ) have been obtained. The cis – gauche enthalpy difference has been determined to be 73±6 cm −1 (209±17 cal / mol ) in krypton and 64±10 cm −1 (183±29 cal / mol ) in xenon with the cis conformer as the more stable form from the variable temperature studies of the infrared spectra (3500–400 cm −1 ). These experimental and theoretical results are compared with the corresponding quantities of some similar molecules.

The Raman (3200–20 cm −1 ) spectra of liquid and solid trans -CH 3 CH CHCH 2 CN, and the infrared (3200–30 cm −1 ) spectra of gaseous and solid trans -3-pentenenitrile have been recorded. The spectra of the fluid phases are consistent with two stable conformers in equilibrium at ambient temperature. The mid-infrared spectra of the sample dissolved in liquid xenon as a function of temperature (−100 to −55°C) have been recorded. Utilizing two conformer pairs, the enthalpy difference has been determined to be 205±7 cm −1 (2.45±0.08 kJ/mol ) with the syn conformer being the more stable form. Vibrational assignments for the 33 normal modes for the syn conformer and several of those for the gauche form are proposed. The structural parameters, dipole moments, conformational stability, and vibrational frequencies have been determined from ab initio calculations. The predicted conformational stability is consistent with the experimental results. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

Mid-infrared spectra (3500–400 cm −1 ) of gaseous and polycrystalline solid ethylcyclobutane have been recorded, as well as the far-infrared (400–50 cm −1 ) spectrum of ethylcyclobutane in the annealed solid phase. Additionally, the Raman spectra (4000–20 cm −1 ) of liquid and annealed solid ethylcyclobutane have also been obtained. Spectroscopic evidence for the coexistence of the equatorial–gauche , axial–gauche and equatorial–cis conformers of the title compound is found in the fluid phase, with the equatorial–gauche rotamer the most stable form, and the only rotamer present in the annealed solid. Ab initio calculations have been carried out with different basis sets up to MP2/6-31G ∗ , from which the structural parameters, conformational stabilities, force constants, infrared and Raman intensities, and vibrational frequencies have been determined. By incorporating the results from the ab initio calculations, a normal coordinate analysis of the title compound has also been performed and this aids in the vibrational assignments of the normal modes. The weak features at 172 and 161 cm −1 in the far-IR and Raman spectra of the solid have been assigned to the ring puckering vibrations, and a theoretically predicted ring-puckering potential function has been determined.

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500 to 400 cm−1) of dimethylmethoxyphosphine, (CH3)2POCH3 and dimethyl(methylthio)phosphine, (CH3)2PSCH3 dissolved in liquid krypton and/or xenon have been recorded. From these data, the enthalpy differences have been determined to be 393±50 cm −1 (4.71±0.60 kJ / mol ), for (CH3)2POCH3 with the near-cis conformer the more stable rotamer and 80±10cm−1 (0.96±0.12 kJ / mol ) for (CH3)2PSCH3 with the cis conformer the more stable form. Complete vibrational assignments are presented for both molecules, which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G(d) calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules.

Variable temperature (−55 to −150°C) studies of the infrared spectra between 4000 and 400 cm −1 of vinyl silyl chloride, CH 2 CHSiH 2 Cl, dissolved in liquid xenon and krypton have been recorded. From the xenon data, the enthalpy difference has been determined to be 78±11 cm −1 ( 0.93±0.13 kJ/mol ) with the gauche conformer the more stable form. However, in the krypton solution the conformational stability could not be determined. The Raman spectra (3500–20 cm −1 ) of liquid and solid, as well as the infrared spectra of the gaseous and solid vinyl silyl-d 2 chloride, have been recorded. Utilizing the isolated silicon-hydrogen stretching frequencies from the CH 2 CHSiHDCl molecule the Si–H distances of 1.479 A were obtained for both conformers. Vibrational assignments are provided for the CH 2 CHSiD 2 Cl molecule for both conformers. Complete equilibrium geometries have been determined for both rotamers using ab initio calculations employing the 6-31G(d), 6-311+G(d,p) and 6-311+G(2d,2p) basis sets at the levels of restricted Hartree–Fock and/or with full electron correlation by the perturbation method, Moller–Plesset, to the second order. Irrespective of the size of the basis set used, the gauche conformer is predicted to be the more stable conformer, which is in agreement with the experimental results. Utilizing previously reported microwave rotational constants for both conformers along with the ab initio predicted structural values, r o parameters have been obtained for both the cis and gauche conformers. The spectroscopic and theoretical results are discussed and compared to the corresponding quantities for some similar molecules.

The far infrared spectrum of gaseous 3,3,3-trifluoropropene, CH 2 CHCF 3 , between 350 and 30 cm −1 has been recorded at a resolution of 0.10 cm −1 . The torsional fundamental for the CF 3 rotor is observed at 83.52 cm −1 . There are three and possibly four “hot bands”, which accompany this fundamental falling to lower wavenumbers with decreasing intensities. Utilizing these torsional data along with structural parameters obtained from MP2/6-311+G** ab initio calculations to calculate the kinetic constant F , the barrier to internal rotation has been determined to be 630±10 cm −1 (7.54±0.12 kJ/mol) and the V 6 term is relatively small with a value of −30±5 cm −1 (−0.36±0.06 kJ/mol). These results are compared to the CH 3 barrier of propene as well as to those of several CF 3 rotors. The harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from both ab initio RHF/6-31G* and MP2/6-31G* calculations and the results compared. Additionally, predicted quantities are compared to the corresponding experimental values when appropriate as well as with some corresponding results for some similar molecules.