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The microwave spectrum of isopropylisocyanate, (CH 3 ) 2 CHNCO, has been investigated from 11,000 to 21,000 MHz and 18 transitions for the more stable trans conformer were assigned and A = 6693.23(15), B = 2263.10(3), C = 1960.05(2) MHz were obtained. By utilizing these rotational constants along with ab initio MP2(full)/6-311 + G(d,p) predicted structural values, adjusted r 0 parameters have been obtained for the trans conformer along with estimated values for the gauche conformer. Variable temperature Raman and infrared spectra of xenon solutions have been recorded and a ΔH value of 115 ± 11 cm −1 (1.38 ± 0.13 kJ/mol) has been determined. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to cc-PVQZ for MP2(full) and 6-311 + G(3df,3pd) for density functional theory calculations by the B3LYP method. From the MP2(full)/cc-PVQZ calculations an energy difference of 87 cm −1 (1.04 kJ/mol) is predicted between the trans and the gauche forms and 168 cm −1 (2.01 kJ/mol) for the cis form which is a transition state.

WOS: 000365367100065, PubMed ID: 26183526, …

The infrared spectra of gaseous and variable-temperature liquid xenon solutions of pyrrolidine have been recorded. The enthalpy difference has been determined to be 109 ± 11 cm(-1) (1.30 ± 0.13 kJ mol(-1)) with the envelope-equatorial conformer more stable than the twist form with 37 ± 3% present at ambient temperature. Ab initio calculations utilizing various basis sets up to MP2(full)/aug-cc-pVTZ have been used to predict the conformational stabilities, energy at the equatorial-axial saddle point, and barriers to planarity. From previously reported microwave rotational constants along with MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained for both conformers. Heavy atom distances (Å) of equatorial[twist] conformer are as follows: N(1)-C(2) = 1.469(3)[1.476(3)], N(1)-C(3) = 1.469(3)[1.479(3)], C(2)-C(4) = 1.541(3)[1.556(3)], C(3)-C(5) = 1.541(3)[1.544(3)], C(4)-C(5) = 1.556(3)[1.543(3)]; and angles (deg)∠N(1)C(2)C(4) = 102.5(5)[107.6(5)], ∠N(1)C(3)C(5) = 102.5(5)[105.4(5)], ∠C(2)C(4)C(5) = 104.3(5)[104.6(5)], ∠C(3)C(5)C(4) = 104.3(5)[103.7(5)], ∠C(2)N(1)C(3) = 104.1(5)[103.9(5)], τC(2)C(4)C(5)C(3) = 0.0(5)[13.5(5)]. A complete vibrational assignment is proposed for both conformers.

The microwave spectra of seven isotopomers of fluoromethylsilane, CH(2)FSiH(3), in the ground vibrational state were measured and analyzed in the frequency range 18-40 GHz. The rotational and centrifugal distortion constants were evaluated by the least-squares treatment of the observed frequencies of a- and b-type R- and b-type Q-transitions. The values for the components of the dipole moment were obtained from the measurements of Stark effects from both a- and b-type transitions and the determined values are: |mu(a)| = 1.041(5), |mu(b)| = 1.311(6), and |mu(t)| = 1.674(4) D. Structural parameters have been determined and the heavy atom distances (r(0)) in Angstroms are: Si-C = 1.8942(57) and C-F = 1.4035(55) and the angle in degree, angleSiCF = 109.58(14). A semi-experimental r(e) structure was also determined from experimental ground state rotational constants and vibration-rotation constants derived from ab initio force fields. The internal torsional fundamental, SiH(3), was observed at 149.2 cm(-1) with two accompanying hot bands at 138.8 and 127.5 cm(-1). The barrier to internal rotation was obtained as 717.3(16) cm(-1) (2.051(46) kcal mol(-1)) by combining the analysis of the microwave A and E splittings and the torsional fundamental and hot band frequencies. Ab initio calculations have been carried out with full electron correlation by the second-order perturbation method with several different basis sets up to MP2/6-311+G(d,p) to obtain geometrical parameters, barriers to internal rotation, and centrifugal distortion constants. Adjusted r(0) structural parameters have been obtained by combining the ab initio MP2/6-311+G(d,p) predicted values with the determined rotational constants for the fluoride as well as with the previously reported microwave data for the chloro- and bromo- compounds. These experimental results are compared to the corresponding parameters for the carbon analogues.

The infrared spectra (3200-50 cm(-1)) of the gas and solid and the Raman spectrum (3200-30 cm(-1)) of liquid and solid fluorocyclopentane, c-C5H9F, have been recorded. Additionally the infrared spectra (3200-400 cm(-1)) of liquid xenon solutions have been recorded at -65 and -95 degrees C. In all of the physical states, only the twisted C(1) conformer was detected. Ab initio calculations utilizing various basis sets up to MP2(full)/6-311+G(2df,2pd) with and without diffuse functions have been used to predict the conformational stabilities. These calculations predict only the twisted C1 conformer as the stable form. The two envelope (C(s) symmetry) forms with axial and equatorial structures were predicted to be first order saddle points with average higher energies of 75 +/- 33 and 683 +/- 44 cm(-1), respectively, from the C1 conformer but lower energies of 2442 and 1812 cm(-1), respectively, than the planar form by MP2 calculations. Similar values were obtained from the corresponding density functional theory calculations by the B3LYP method. A complete vibrational assignment is given for the twisted (C1) conformer which is supported by normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations. The adjusted r0 structural parameters have been obtained by systematically fitting the MP2(full)/6-311+G(d,p) predicted values with the rotational constants obtained from a microwave study. The determined heavy atom r0 distances in A are (C1C2) = 1.531(3), (C1C3) = 1.519(3), (C2C4) = 1.553(3), (C3C5) = 1.533(3), (C4C5) = 1.540(3), and (C1F6) = 1.411(3) and the angles in degrees are angle C3C1C2 = 105.5(5), angle C1C2C4 = 106.2(5), angle C1C3C5 = 102.9(5), angle F6C1C2 = 108.9(5), and angle F6C1C3 = 107.6(5) with a dihedral angle angle C2C4C5C3 = 25.3(3). These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

The FT-microwave spectrum (6.5-26 GHz) of (chloromethyl)fluorosilane (ClCH2-SiH2F) has been recorded and 250 transitions for the parent species along with C-13, Cl-37, Si-29, and Si-30 isotopologues have been assigned for trans conformer. Infrared spectra (3100 to 400 cm(-1)) of gas, solid, and the variable temperature (-100 to -60 degrees C) studies of the infrared spectra of the sample dissolved in xenon have been recorded. Additionally, the variable temperature (-153 to -133 degrees C) studies of the Raman spectra of the sample dissolved in krypton have been recorded. The enthalpy difference between the trans and gauche conformers in xenon solutions has been determined to be 109 +/- 15 cm(-1) (1.47 +/- 0.16 kJ mol(-1), and in krypton solution, the enthalpy difference has been determined to be 97 +/- 16 cm(-1) (1.16 +/- 0.19 kJ mol(-1)) with the trans conformer as the more stable form. Approximately 46 +/- 2% of the trans form is present at ambient temperature. By utilizing the microwave rotational constants of five isotopologues for trans and the structural parameters predicted from MP2(full)/6-311+G(d,p) calculations, adjusted r(0) parameters have been obtained for trans conformer. The r(0) structural parameter values for the trans form are for the heavy atom distances (angstrom): Si-F = 1.608 (3); C-Cl = 1.771 (3); Si-C = 1.884 (3); and angles (deg): angle FSiC = 108.9 (5); angle ClCSi = 104.9 (5). The results are discussed and compared to some related molecules.

The infrared spectrum (3100–300 cm −1 ) in the gas phase and Raman spectrum (3100–150 cm −1 ) of the liquid of cyclobutyldichlorosilane (c-C 4 H 7 SiHCl 2 ) have been recorded. Variable temperature (−143 °C to −123 °C) studies of the Raman spectra (3100–300 cm −1 ) dissolved in liquid krypton have been carried out. From these data, the experimental stabilities of the conformer have been determined to be Eq-g > Ax-t > Eq-t > Ax-g. The enthalpy difference between Eq-g and Ax-t has been determined from band pairs to be 85 ± 10 cm −1 (1.01 ± 0.11 kJ mol −1 ) with the Eq-g conformer the more stable form. The enthalpy difference between Eq-g and Eq-t is 116 ± 43 cm −1 (1.39 ± 0.52 kJ mol −1 ) and the enthalpy difference between Eq-g and Ax-g has been determined to be 138 ± 42 cm −1 (1.66 ± 0.51 kJ mol −1 ) with the Eq-g conformer as the more stable form. The percentage of the equatorial gauche conformer is estimated to be 47% at ambient temperature. To support the spectroscopic study, ab initio calculations by the Moller–Plesset perturbation method to second order MP2(full) and density functional theory calculations by the B3LYP method have been carried out. The infrared intensities, Raman activities, vibrational frequencies and band contours have been predicted from MP2(full)/6-31G(d) calculations and these theoretical values are compared to the experimental ones when available. The conformational stabilities have been predicted from theoretical calculations with basis sets up to 6-311+G(2d,2p) from both MP2(full) and density functional theory calculations by the B3LYP method. The results are discussed and compared to the corresponding properties of some related molecules.

The infrared spectra (3200–30 cm–1) of ethyl bromogermane, CH3CH2GeH2Br, in the gaseous phase and of amorphous and annealed solid samples as well as the Raman spectrum (3200–100 cm–1) of the liquid have been recorded. Variable-temperature (–105 to –150 °C) studies of the infrared spectra of a sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference between the gauche and trans conformers has been determined to be 158 ± 16 cm–1 (1.89 ± 0.20 kJ/mol), with the gauche conformer being the more stable form. This result 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 at ambient temperature 81 ± 2% of the sample is in the gauche form. A relatively complete vibrational assignment is proposed for both the gauche and trans 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 and conformational stabilities 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). Additionally, the potential functions governing the conformation interchange have been estimated from ab initio MP2/6-31G(d) and density functional theory calculations by the B3LYP method, with barriers to conformational interchange of 560, 924, and 852 cm–1 from MP2/6-31G(d) and 418, 771, and 606 cm–1 from B3LYP/6-31G(d) calculations for the trans to gauche, gauche to gauche, and gauche to trans conformers, respectively. The results are discussed and compared to some corresponding quantities for several related molecules.Key words: conformational stability, Raman spectra, infrared spectra; ab initio calculations, ethyl bromogermane.

Variable-temperature (−55 to −100 °C) studies of the infrared spectra (3500 to 400 cm-1) of fluoromethylcyclopropane, c-C3H5CH2F, dissolved in liquefied xenon have been carried out, and the Raman (liquid and solid) and infrared (gas and solid) spectra have been recorded from 3500 to 60 cm-1. By utilizing four conformer pairs, an enthalpy difference of 262 ± 26 cm-1 (3.13 ± 0.31 kJ/mol) was obtained, with the gauche rotamer the more stable conformer and the only form present in the solid. The abundance of cis conformer present at ambient temperature is 12 ± 1%. On the basis of the far-infrared spectral data along with the experimental enthalpy and gauche dihedral angle, the potential function governing conformational interchange has been obtained, and the determined potential constants are V1 = −245 ± 23, V2 = −414 ± 17, V3 = 1263 ± 6, V4 = 272 ± 17, and V5 = 101 ± 2 cm-1, with the cis-to-gauche barrier of 1223 cm-1 (14.63 kJ/mol) and the gauche-to-gauche barrier of 1362 cm-1 (16.29 kJ/mol). From MP2 ab in...

Infrared (3500-50 cm - 1 ) spectra of gaseous and Raman (3500-50 cm - 1 ) spectra of liquid aminomethyl cyclopropane (cyclopropyl methylamine), c-C 3 H 5 CH 2 NH 2 have been recorded. Additional variable temperature (-55 to -100 °C) studies of the mid-infrared (3500-400 cm - 1 ) spectra of the sample dissolved in liquid xenon as well as variable temperature (-79 to -112 °C) studies of the far-infrared spectra (600-50 cm - 1 ) of krypton solutions have been obtained. From these data the enthalpy difference has been determined to be 109 ′ 11 cm - 1 (1.30 ′ 0.13 kJ/mol) between the most stable gauche-gauche-1 (Gg-1) conformer (the first gauche designation, capital G, for the heavy atom conformation along the C-C bond, and the second gauche designation, lower case g, for the amino torsion along C-N bond) and the second most stable conformation, gauche-trans (Gt). The third most stable conformer is the cis-gauche (Cg) form with an enthalpy difference of 267 ′ 28 cm - 1 (3.19 ′ 0.33 kJ/mol) to the most stable conformer. Larger enthalpy values of 400 ′ 40 cm - 1 and 480 ′ 48 cm - 1 were obtained for the Gg-2 and Ct conformers, respectively. From these data, the following conformer percentages are estimated at ambient temperature: 49% Gg-1, 29% Gt, 13% Cg, 7% Gg-2, and 2%, Ct. Ab initio calculations have been carried out with several different basis sets up to MP2/ 6-311G(2df,2pd) as well as with diffuse functions to determine the conformational stability. Without diffuse functions, the Gt conformer is predicted as the most stable conformer, whereas with diffuse functions, the Gg- 1 form is predicted to be the most stable rotamer, and the density functional calculations by the B3LYP method with the same corresponding basis sets all predict the Gt form as the most stable conformer. Additionally, force constants, infrared intensities, Raman activities, depolarization ratios, and scaled vibrational frequencies have been determined from MP2/6-31G(d) calculations. Vibrational assignments are provided for most of the fundamentals for the Gg- 1 and Gt conformers. Adjusted r 0 structural parameters have been obtained by combining ab initio MP2/6-311+G(d,p) predicted values and previously reported microwave data for the Gg-1 and Gt forms. Many of the determined results are compared to the corresponding parameters for some other similar organoamines.

The infrared spectra (3500-50 cm - 1 ) of gas and solid and the Raman spectra (3500-50 cm - 1 ) of liquid and solid 1-penten-4-yne, CH 2 =CHCH 2 C≡CH, have been recorded. Variable-temperature studies over the range - 105 to -150 °C of the infrared spectra (3500-400 cm - 1 ) of the sample dissolved in liquid krypton have also been recorded. By utilizing the relative intensities of five syn/gauche conformer pairs, the syn conformer is found to be the lower energy form with an enthalpy difference of 248 ′ 25 cm - 1 (2.97 ′ 0.30 kJ/mol). At ambient temperature it is estimated that there is 38% ′ 2% of the gauche conformer present. Equilibrium geometries and total energies of the two conformers have been determined from ab initio calculations with full electron correlation by the perturbation method to second order as well as by hybrid density functional theory (DFT) calculation with the B3LYP method using a number of basis sets. The smaller basis sets with diffuse functions predict the gauche conformer to be the more stable form, whereas other calculations predict the syn conformer to be the lower energy rotamer. The B3LYP calculations predict a much lower energy difference between the conformers than found experimentally. A complete vibrational assignment is proposed for the syn conformer and many of the fundamentals have been identified for the gauche form on the basis of the force constants, relative intensities, and depolarization ratios obtained from MP2/6-31(d) ab initio calculations as well as on rotational-vibrational band contours obtained from the predicted equilibrium geometric parameters. The r 0 structural parameters are estimated for 1-penten-4-yne from ab initio MP2/6-311 +G(d,p) calculations, and comparisons are made with those of allyl fluoride and cyanide. The spectroscopic and theoretical results are compared to the corresponding properties for 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 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 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 (3300−10 cm-1) of gaseous, liquid, and solid 3,3-difluorobutene, CH2CHCF2CH3, and the infrared spectra (3400−60 cm-1) of the gas, xenon solution, and solid have been recorded. The...

The far-infrared and infrared spectra of gaseous dimethylallene (3-methyl-1,2-butadiene), (CH3)2CCCH2, were measured as well as the Raman spectra of the compound in all three physical phases. The spectra were assigned using infrared band contours, Raman depolarization ratios and ab initio predicted harmonic frequencies and intensities as criteria. The torsional energy level splittings were determined for the ground state and one torsional excited state from previously published microwave spectra by fitting the frequencies to an effective rotational Hamiltonian for molecules with two periodic large-amplitude motions. The splittings and the data from the far-infrared spectrum were used to derive the two-dimensional torsional potential function of dimethylallene. This function with an effective barrier V3eff = 726(4) cm-1 is compared with the results from the microwave analysis and with the potential function calculated by a number of ab initio methods (among them B3LYP/6-31G(d) and MP2/DZ(d)).

The infrared (3500 to 30 cm-1) spectra of gaseous and solid and the Raman (3500 to 20 cm-1) spectra of the liquid [with quantitative depolarization ratios] and solid cyclopropylmethylacetylene, c-C3H5CH2CCH (ethynylmethylcyclopropane), have been recorded. Additionally, variable temperature (−55 to −100 °C) studies of the infrared spectra (3500 to 400 cm-1) of the title compound dissolved in liquid xenon have been carried out. Utilizing four conformer pairs, an enthalpy difference of 147 ± 14 cm-1 (1.76 ± 0.17 kJ/mol) was obtained, with the cis rotamer the more stable conformer. At ambient temperature there is approximately 48% of the cis conformer present. However, the gauche conformer remains in the annealed solid. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies are reported for both conformers from ab initio calculations. The calculations were carried out at the restricted Hartree−Fock...

The Raman spectra (3300 to 10 cm-1) of gaseous, liquid, and solid difluoromethylcyclopropane, c-C3H5CF2H, and the infrared spectra (3400 to 60 cm-1) of the gas and solid have been recorded. The spectra of the fluid phases are consistent with two stable conformers in equilibrium at ambient temperature. These spectral data have been interpreted on the basis that the cis conformer (H atom of the difluoromethyl group is cis to the three-membered ring) is more stable than the gauche form in both the gaseous and liquid phases, and it is the only rotamer present in the solid. The mid-infrared spectra of the sample dissolved in liquid xenon as a function of temperature (−100 to −60 °C) have been recorded. Utilizing two conformer pairs, the enthalpy difference has been determined to be 102 ± 8 cm-1 (1.22 ± 0.10 kJ/mol) with the cis conformer the more stable form. The enthalpy difference has also been determined to be 145 ± 48 cm-1 (1.73 ± 0.57 kJ/mol) for the liquid from the temperature-dependent Raman spectra. Th...

The far-infrared spectrum has been recorded from 50 to 360 cm-1 at a resolution of 0.10 cm-1 for normal propanal CH3CH2CHO and for the three isotopic species CH3CH2CDO, CH3CD2CHO, and CD3CD2CHO. Along with the fundamental asymmetric torsional transition, several hot band transitions of the cis conformer have been observed and assigned for each isotopic species. The geometrical structures of the cis and gauche conformers have been determined by ab initio calculations in order to compare them with previously reported microwave structures and to calculate inertial constants for the two internal rotations. A wide range of basis sets and ab initio theoretical methods up to MP4 have been used in order to determine the cis to gauche conformational energy difference. Using both the observed and calculated data, along with the previously reported gauche dihedral angle and microwave splittings for the gauche ground state for the CH3CH2CHO and CH3CH2CDO molecules, the asymmetric torsional potential function has been...

The infrared (3300−30 cm-1) spectra of gaseous and solid cyclopropylchlorosilane, c-C3H5SiH2Cl, have been recorded. Additionally, the Raman spectra (3200−30 cm-1) of the liquid and solid have been ...

The far infrared spectrum of 1-pentyne, CH3CH2CH2C⋮CH, has been recorded in the gas phase. The fundamental asymmetric torsional transitions have been observed at 114 and 109 cm-1 for the gauche (synclinal) and trans (antiperiplanar; methyl group trans to the acetylenic group) conformers, respectively. The methyl torsional fundamental (249.8 cm-1) has only been observed for the gauche conformer. Infrared spectra (3500−400 cm-1) of 1-pentyne dissolved in liquid xenon have been recorded from which variable temperature (−60 to −100 °C) studies have been carried out. From these data, the enthalpy difference has been determined to be 113 ± 26 cm-1 (323 ± 74 cal/mol) with the trans conformer more stable than the gauche form. The Raman spectrum (3500−40 cm-1) has also been recorded of the liquid to aid in the assignment of the fundamentals. Ab initio electronic structure calculations of energies, conformational geometries, vibrational frequencies, and potential energy functions have been carried out to complement...

The FT-microwave spectrum of cyclobutylcarboxylic acid chloride, c-C4H7C(O)Cl, has been recorded and 153 transitions for the (35)Cl and (37)Cl isotopologues have been assigned for the gauche-equatorial (g-Eq) conformation. The ground state rotational constants were determined for (35)Cl [(37)Cl]: A = 4349.8429(25) [4322.0555(56)] MHz, B = 1414.8032(25) [1384.5058(25)] MHz, and C = 1148.2411(25) [1126.3546(25)] MHz. From these rotational constants and ab initio predicted parameters, adjusted r0 parameters are reported with distances (Å) rCα-C = 1.491(4), rC═O = 1.193(3), rCα-Cβ = 1.553(4), rCα-Cβ' = 1.540(4), rCγ-Cβ = 1.547(4), rCγ-Cβ' = 1.546(4), rC-Cl = 1.801(3) and angles (deg) τCγCβCβ'Cα = 30.9(5). Variable temperature (-70 to -100 °C) infrared spectra (4000 to 400 cm(-1)) were recorded in liquid xenon and the g-Eq conformer was determined the most stable form, with enthalpy differences of 91 ± 9 cm(-1) (1.09 ± 0.11 kJ/mol) for the gauche-axial (g-Ax) form and 173 ± 17 cm(-1) (2.07 ± 0.20 kJ/mol) for the trans-equatorial (t-Eq) conformer. The relative amounts at ambient temperature are 54% g-Eq, 35 ± 1% g-Ax, and 12 ± 1% t-Eq forms. Vibrational assignments have been provided for the three conformers and theoretical calculations were carried out. The results are discussed and compared to corresponding properties of related molecules.

The infrared and Raman spectrum of 1,2-dichloropropane has been reinvestigated and is reported in the gas, liquid, amorphous solid and two crystal modifications. All three conformers are present in disordered phases and many bands are composites of overlapping contributors. Assignments of observed bands are substantiated with the aid of ab initio calculations utilizing the RHF/3-21G and RHF/6-31G∗ basis sets. Electron correlation was approximated by an MP2/6-31G∗ calculation for all three conformers. From the temperature dependence of the Raman spectrum of the liquid, the bands at 528 and 671 cm−1 were uniquely assigned, respectively, to the conformer with the hydrogen atom trans to the chlorine atom (G−) and the chlorine atom trans to the chlorine atom (A), and an average enthalpy difference for the liquid phase was found to be 130 cm−1 (370 cal mol−1) at −57°C. In contrast, an enthalpy difference of 1038 cm−1 was obtained from the ab initio calculations for the isolated molecule using the RHF/3-21G basis set and 561 cm−1 (1.605 kcal mol−1) from the MP2/6-31G∗ calculation. The enthalpy difference showed experimental variation with temperature, corresponding to a more highly associated liquid at −105°C than at 60°C. The scaled harmonic force fields obtained using the MP2/6-31G∗ calculation are reported for all three conformers together with potential energy distributions and scaled and unscaled frequencies calculated from these force fields. These results are compared to those obtained for some similar molecules.

The Raman (50 to 3200 cm−1) and infrared (50 to 3500 cm−1) spectra of chlorodimethylmethoxysilane, Cl(CH3)2SiOCH3, in the vapor and solid phases have been recorded. Raman spectra of the liquid including depolarization ratios have also been recorded. Optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing the RHF/3–21G* and RHF/6–31G* basis sets. The calculations from both of these basis sets indicated the gauche conformer to be significantly more stable than the trans conformer. Since the gauche has twice the multiplicity of the trans form it is unlikely that the trans conformer will be detected in the fluid phases at room temperature. This is supported by the fact that no infrared or Raman bands were found to vanish in the spectra of the crystalline solid. The vibrational frequencies have been calculated using appropriate scaling factors, and the vibrational spectra are interpreted in detail. The results have been compared with those obtained for some related molecules.

The Raman (3200−10 cm−1) and infrared (3200−20 cm−1) spectra of gaseous and solid cis-1,3-dichloropropene, cis-ClHC=CHCH2Cl, have been recorded. Additionally, the Raman spectrum of the liquid with qualitative depolarization data has also been obtained. These spectral data have been interpreted on the basis that the molecule exists predominantly in the gauche (allylic chlorine atom oriented gauche to the double bond) conformation in all physical phases. Some bands in the infrared spectrum of the gas could be due to a second higher energy conformer but the lack of corresponding Raman bands casts doubt on such an assignment. Ab initio Hartree–Fock gradient calculations employing the RHF/6-31G* basis set are consistent with two minima that correspond to the two equivalent gauche forms for the potential surface for the internal rotation about the C—C bond. These minima occur at dihedral angles, [Formula: see text] ClCCC, of 122° and 238° (0° corresponds to the syn conformation) and the gauche to gauche barrier at the 180° transition state, which corresponds to the anti structure, is 342 cm−1. The barrier from the gauche minima to the syn (0°) structure, which is also a transition state, is 2425 cm−1. Complete equilibrium geometries for the gauche structure have been determined with the RHF/3-21G*, RHF/6-31G*, and MP2/6-31G* basis sets. A normal coordinate analysis utilizing a harmonic force field calculation with the RHF/3-21G* basis set has been carried out for the gauche conformer. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.

The FT-microwave spectrum of germylcyclohexane, c-C(6)H(11)GeH(3), has been recorded, and more than 40 transitions for the (70)Ge, (72)Ge, and (74)Ge isotopomers (isotopologues) have been assigned for the chair-equatorial conformer. The heavy atom adjusted r(0) structural parameters have been determined [distances, C(gamma)-C(delta) = 1.533(3) A, C(gamma)-C(beta) = 1.532(3) A, C(alpha)-C(beta) = 1.540(3) A, C(alpha)-Ge = 1.957(3) A; angles, angleC(gamma)C(delta)C(beta) = 111.2(5) degrees , angleGeC(alpha)C(beta) = 111.1(5) degrees , with the dihedral angle angleC(gamma)C(delta)C(beta)C(alpha) = 55.6(10) degrees ]. Raman and/or infrared spectra of gas, liquid, and solid germylcyclohexane have been recorded. The temperature dependency of the Raman spectrum of the conformer pair 712 (equatorial)/683 (axial) cm(-1) gives an enthalpy difference of 453 +/- 38 cm(-1) (1.30 +/- 0.11 kcal/mol) with the chair-equatorial conformer the more stable form. At ambient temperature, the abundance of the axial conformer is 11 +/- 1%. Substituent effects on the enthalpy difference and structure of monosubstituted cyclohexanes are discussed for a number of molecules.

Rotational spectra for 3 silicon i so t o pologues ( 28 Si, 29 Si, 30 Si) of cyclopropylmethylsilane (c-C 3 H 5 SiH 2 CH 3 ) have been observed in natural abundance using Fourier-transform microwave spectroscopy, and the dipole moment of the most abundant ( 28 Si) isotopologue has been determined using the Stark effect. The observed rotational constants (A = 8800.5997(9) MHz; B = 2238.6011(3) MHz; C = 2001.0579(3) MHz) and dipole moment components (μ a = 0.195(2) D, μ b = 0.674(11) D, μ c = 0.362(19) D, μ total = 0.790(13) D) for the 28 Si species are consistent with ab initio predictions (MP2/6-311 + G(d)) for a gauche conformation about the Si-cyclopropyl bond. All of the observed transitions were split into doublets due to internal rotation of the methyl group, allowing a determination of the V 3 barrier to internal rotation of 6.671(9) kJ mol ―1 for the most abundant isotopologue. This barrier will be compared to those for other Si-CH 3 containing compounds and will be related to a partial structure determination from the available microwave and ab initio data.

The Raman spectra (3200–50 cm−1) of gaseous, liquid, and solid 2-chloropropane-d3 (isopropyl-d3 chloride), CH3(CD3)CHCl, and the infrared spectra (3200–50 cm−1) of the gas and solid have been recorded. The torsional transitions observed in the far infrared spectrum of the gaseous sample recorded at a resolution of 0.10 cm−1 between 265 and 135 cm−1 were analyzed in terms of the semirigid rotor model. An effective barrier of 1378 ± 4 cm−1 (3.94 ± 0.01 kcal/mol), cosine–cosine coupling term of 166 ± 10 cm−1 (0.47 ± 0.03 kcal/mol), and sine–sine coupling term of −173 ± 1 cm−1 (−0.49 ± 0.01 kcal/mol) were determined by fitting ten observed frequencies arising from the CH3 and CD3 torsions. The assignment of the 27 fundamentals is given and discussed. A complete equilibrium geometry, barrier to internal rotation, and vibrational frequencies have been determined by ab initio Hartree–Fock gradient calculations employing either 3-21G* or 6-31G* basis sets for both the d0 and d3 species. These calculated results are compared to the experimental values as well as to the corresponding quantities for some similar molecules. Key words: 2-chloropropane, vibrational spectrum; ab initio calculations; barrier to internal rotation.

The relative stabilities of the five conformers of allyl amine, a medium-size aliphatic molecule, were estimated by applying ab initio quantum mechanical methods at several levels of theory. The second-order Moller-Plesset perturbation method (MP2), quadratic configuration interaction including single and double excitations (QCISD), coupled-cluster with single and double excitations (CCSD) and CCSD plus perturbative triple excitations [CCSD(T)] were applied. The Dunning correlation consistent basis sets (through aug-cc-pVQZ and cc-pV5Z) were employed. The MP2 energies relative to the energy of the cis-trans conformer reported here appear to approach the basis set limit. The predicted allyl amine conformer energies approaching the Hartree-Fock basis set limit are 158 cm -1 (cis-gauche), -5 cm -1 (gauche-trans), and -146 cm -1 (gauche-gauche). The same three relative energies near the MP2 basis set limit are 135, 103, and 50 cm -1 , respectively. The analogous energies deduced from experiment are 173 ± 12, 92 ± 8, and 122 ± 5 cm -1 . The theoretical results obtained in the present study suggest that satisfactory predictions of the conformer energetics of allyl amine may be achieved only by theoretical methods that incorporate consideration of correlation effects in conjunction with large basis sets. Evaluation of the zero-point vibrational energy corrections is critical, due to the very small classical energy differences between the five conformers of allyl amine. Agreement between theory and experiment for the gauche-gauche conformational energy remains problematical.

The microwave spectra of (methylamino)thiophosphoryl difluoride, CH(3)NHP(=S)F(2), and two deuterated species, CH(3)NDP(=S)F(2) and CD(3)NHP(=S)F(2), have been investigated in the region from 26.5 to 39.0 GHz. The rotational constants of the ground vibrational state have been determined and have been shown to be only consistent with the trans conformer (CH(3) group antiperiplanar to the P=S bond) with C(s) symmetry. The a-type R branch transitions have been assigned for the trans conformer for the three isotopomers on the basis of the rigid rotor model. Near-trans and near-cis forms without molecular planes of symmetry are predicted by all ab initio calculations with the near-trans form being more stable. However, the double-well potentials governing the interchange between the two enantiomeric near-trans as well as the two near-cis forms are too shallow to accommodate the zero-point energies of the nu(24) asymmetric torsion. Thus, the trans conformation with C(s) symmetry may be more accurate in explaining the microwave experimental data. The "adjusted" r(0) structural parameters have been obtained by systematically adjusting the ab initio MP2(full)/6-311+G(d,p) structure of the trans conformer with C(s) symmetry to fit the microwave rotational constants. The determined heavy atom distances are r(C-N) = 1.459(5), r(P-N) = 1.621(5), r(P=S) = 1.879(5), and r(P-F) = 1.550(5) A, and the heavy atom angles are angleCNP = 124.7(5) degrees , angleNPS = 118.3(5) degrees , angleNPF = 103.2(5) degrees , angleFPS = 117.0(5) degrees , and angleFPF = 94.6(5) degrees . The adjusted r(0) parameters have also been obtained for aminodifluorophosphine, H(2)NPF(2), with a slightly pyramidal -PNH(2) moiety. The results indicate that the previously reported short distance of 0.981(5) A for the N-H(o)(outer) bond from the microwave study is too short, and the adjusted r(0) value of 1.007(3) A is obtained from the combined data. Adjusted r(0) parameters are also reported for (dimethylamino)difluorophosphine, (CH(3))(2)NPF(2), with C(s) symmetry with the PNC(2) portion of the molecule being planar. The previously reported C-H distances from the electron diffraction study are too long, and the anglePNC(i) and angleC(o)NC(i) angles are also found to be in error. These results provide a reasonable explanation why the microwave and electron diffraction results differ for the structures of these latter two molecules.

The infrared (3500 to 300 cm−1) spectra of methylisothiocyanate, ethylisothiocyanate, isopropylisothiocyanate, and cyclopropylisothiocyanate isolated in argon and nitrogen matrices have been recorded. In general, the spectra were more complex in the nitrogen matrices and, for ethylisothiocyanate, nearly all of the fundamentals appeared as doublets in the nitrogen matrix but for the most part as single bands in the argon matrix. No evidence could be found for a second conformer for either ethylisothiocyanate or isopropylisothiocyanate. Even though cyclopropylisothiocyanate has been shown to exist as the cis and trans conformers at ambient temperature, little conclusive evidence could be found for two isomers in the infrared matrix material. The complex spectra observed in the NCS antisymmetric stretching region as well as in the 520 cm−1 region appear to arise in part from combinations involving the low-frequency large amplitude CNC bend or asymmetric torsion of these organoisothiocyanate molecules. It appears that the vibrational spectra of these molecules are not sensitive to the orientation of the NCS moiety.

The infrared, Raman, and microwave spectra of gaseous ethaneselenol have been investigated. The rotational constants for both the more stable gauche and for the trans conformers are reported for the Et 78 SeH, Et 78 SeD, Et 80 SeH, and Et 80 SeD isotopic species. A proposed structure has been derived from a least-squares analysis of the moments of inertia. Dipole moment components have been obtained from each conformer using second-order Stark effects. For the gauche conformer, they are μ a = 1.42 ± 0.01, μ c = 0.37 ± 0.03, and μ total = 1.47 ± 0.01 D. For the trans isomer they are μ a = 1.217 ± 0.002, μ b = 0.850 ± 0.001, and μ total = 1.485 ± 0.002 D. The methyl barrier to internal rotation was calculated using observed frequencies obtained from the infrared and Raman spectra; a value of 3.59 ± 0.01 kcal/mole was obtained. Asymmetric potential functions have been calculated for both the EtSeH and EtSeD isotopic species. For the light species the potential constants for internal rotation around the CSe bond are V 2 = −96.4 ± 1, V 3 = 432 ± 4, and V 6 = −20 ± 2 cm −1 . The difference between ground-state energy levels of the two conformers was found to be 66 cm −1 . A vibrational assignment based on infrared and Raman spectra of the gaseous phase is presented.

The microwave spectra from 12.5 to 39.0 GHz of CH3SnH2D, CH3SnHD2, and CH3SnD3 have been measured and assigned for the ground vibrational state for the three most naturally abundant tin isotopes, 120Sn, 118Sn, and 116Sn. From a diagnostic least-squares adjustment to fit 20 rotational constants, the following ro structural parameters were obtained: r(Sn-H) = 1.708 ± 0.001 A, r(CSn) = 2.140 ± 0.001 A, r(CH) = 1.083 ± 0.005 A

The microwave spectrum of ethylcyanide- d 5 has been recorded from 18.0 to 40.0 GHz. Both a -type and b -type transitions were observed and assigned. Also, the R -branch assignments have been made for three excited states of the internal torsional mode and two excited states of the CN inplane bending mode as well as an excited vibrational state involving both of these motions. The barrier to internal rotation was determined to be 3.00 ± 0.15 kcal/mole from the E , A splittings of the third excited state. The quadrupole coupling constants of the 14 N nucleus were found to have values of −3.213, 1.168, and 2.045 MHz for χ aa , χ bb , and χ cc , respectively. These results are compared to those previously obtained on the corresponding hydrogen compound.

The microwave spectrum of 1,1,2,2-tetrafluorocyclobutane, C 4 H 4 F 4 , has been recorded from 26.5 to 40.0 GHz. The molecule is a b -type rotor. The R -branch assignments have been made for the ground state and four vibrationally excited states. Excited states of the CF 2 bending and the ring puckering modes have been assigned. Splitting was observed in the excited state of the ring puckering mode indicating that the molecule is puckered. From intensity measurements, the frequency for the 2 ← 0 and 3 ← 1 ring puckering transitions was calculated to be 80 ± 15 cm −1 . The dipole moment was determined by the Stark effect to be μ b = 3.17 ± 0.03 D.

The multiplet splitting patterns of microwave transitions in the ground state and the first two torsional excited states of CH3OCH3, CD3OCD3, and CD3OCH3 were analyzed in terms of the semirigid rotor models C2vF-C3vT-C3vT and C 3 F- C 3v T- C 3v T . The following nonzero potential coefficients were obtained for CH3OCH3: V30 = V03 = 909.05 ± 0.49 cm−1, V′33 = 5.06 ± 1.60 cm−1; for CD3OCH3: V30(CD3) = 897.18 ± 2.41 cm−1, V03(CH3) = 910.45 ± 0.33 cm−1; for CD3OCD3: V30 = V03 = 897.00 cm−1. These results are compared to earlier microwave studies of these molecules.

The microwave spectra of cis-glyoxal-d1 (C2HDO2) and cis-glyoxal-d2 (C2D2O2) have been obtained and assigned in the range from 18 to 40 GHz. The determined rotational constants for C2HDO2 were: A = 23857.40 ± 0.36, B = 6075.89 ± 0.09, and C = 4849.65 MHz; and for C2D2O2, A = 21521.82 ± 0.21, B = 5968.99 ± 0.04, and C = 4680.61 ± 0.05 MHz. By using these rotational constants along with those for the light molecule and an assumed CO bond length of 1.207 A, the following structural parameters were obtained from a least-squares fit: r CC) = 1.514 A , r (CH) = 1.130 A ,∢CCO = 123.4°, and ∢CCH = 116.2°. It was found that the carbon-carbon bond distance was the only structural parameter which was significantly affected by the assumed carbon-oxygen bond distance.

The microwave spectrum of methyltrichlorogermane has been investigated in the region 26.5 to 40.0 GHz. The ground state rotational constants, B , were found to be 1602.19, 1601.42, 1601.10, 1600.71, 1600.02, 1537.84, 1537.10, and 1536.36 MHz for the symmetric top molecules CH 3 70 Ge 35 Cl 3 , CH 3 72 Ge 35 Cl 3 , CH 3 73 Ge 35 Cl 3 , CH 3 74 Ge 35 Cl 3 , CH 3 76 Ge 35 Cl 3 , CH 3 70 Ge 37 Cl 3 , CH 3 72 Ge 37 Cl 3 , and CH 3 74 Ge 37 Cl 3 , respectively. For the asymmetric top molecules CH 3 72 Ge 35 Cl 2 37 Cl and CH 3 74 Ge 35 Cl 2 37 Cl the ground state rotational constants A , B , and C were found to be 1597.96, 1559.31, 1203 and 1597.17, 1558.59, 1207 MHz, respectively. From the rotational constants the r s values for the GeCl bond distance of 2.135 ± 0.006 A and the CGeCl bond angle of 106.0 ± 0.7° were obtained. The centrifugal distortion constant for the CH 3 Ge 35 Cl 3 species was calculated to be 0.35 ± 0.08 kHz. The Raman spectra of methyltrichlorogermane has been recorded in the gas phase and the methyl torsional overtone (Δ ν = 2) was observed. From the observed frequency shift the barrier to internal rotation has been calculated to be 1.45 kcal/mole.

The microwave spectrum of isopropyliodide was studied in the 18.0 to 26.5 GHz region. From observed a -type R -transitions, the rotational constants A , B , C and the quadrupole coupling constants χ aa , χ bb , χ cc , and χ ac were determined using diagonalization of the complete Hamiltonian matrix including all quadrupole operator matrix elements. The results are consistent with those of the homologous series (CH 3 ) n CH 3− n I, n = 0, 1, 2, 3.