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The Raman spectra (3400–10 cm−1) of gaseous, liquid and solid and the infrared spectra (3500–35 cm−1) of gaseous and solid cyanomethyl methyl ether (methoxyacetonitrile), (CN)CH2OCH3, were recorded. The farinfrared spectrum of the gas was recorded at a resolution of 0.10 cm−1 in the region from 370 to 30 cm−1. The fundamental asymmetric torsions of the gauche and trans conformations were observed at 112.5 and 104.6 cm−1, respectively, with the gauche form having two excited-state transitions falling to lower wavenumber. From these data, along with the enthalpy difference and gauche dihedral angle, the asymmetric torsional potential function was calculated with the following coefficients: V1 = 153 ± 9, V2 = −619 ± 8, V3 = 1000 ± 2 and V4 = −100 ± 2 cm−1. From this potential function, the trans to gauche, gauche to gauche and gauche to trans barriers were determined as 512, 1592 and 951 cm−1, respectively, with an enthalpy difference of 439 ± 19 cm−1 (1255 ± 54 cal mol−1) and the gauche conformer the more stable form in the gas phase. The enthalpy difference was also determined experimentally from variable-temperature studies of the Raman spectrum and a value of 337 ± 44 cm−1 (964 ± 126 cal mol−1) was obtained for the liquid with the gauche form more stable. Additionally, the symmetric methyl torsions of both gauche and trans forms were observed at 170.4 and 217.6 cm−1, respectively. On the basis of a one-dimensional model, the barrier to internal rotation of the methyl moiety was determined as 839 cm−1 (2.40 kcal mol−1) for the guache conformer and 947 cm−1 (2.71 kcal mol−1) for the trans form. A complete vibrational assignment is proposed for a gauche-trans equilibrium in the gas and liquid phases from the Raman (3200–10 cm−1) and infrared (3200–35 cm−1) spectra, but in the solid state only the gauche conformer remains. The structural parameters, conformational stability, barriers to internal rotation and fundamental vibrational frequencies which were determined experimentally were compared with those obtained from ab initio calculations employing the RHF/4–31G*, RHF/6–31G* and MP2/6–31 + + G** basis sets. These results were compared with the corresponding quantities obtained for some similar molecules.

Raman (3200 to 10 cm −1 ) and infrared (3200 to 50 cm −1 ) spectra have been recorded for the fluid and solid phases of trans -1-chloro-2-butene (crotyl chloride, trans -CH 3 CHCHCH 2 Cl), and a complete vibrational assignment is proposed. The fundamental asymmetric torsion for the more stable gauche conformer has been observed in the far infrared spectrum of the gas and has a hybrid contour centered at 82.5 cm −1 . The corresponding mode for the syn conformer (allylic chlorine atom oriented syn to the double bond) gives rise to a series of well defined C -type Q -branches beginning at 110.7 cm −1 and proceeding to lower frequencies. From these data the potential function governing internal rotation of the asymmetric top has been determined and the following potential coefficients have been obtained: V 1 = −371 ± 18, V 2 = −103 ± 9, V 3 = 662 − 30, V 4 = 123 ± 5, V 6 = −20 ± 12 cm −1 . This potential function has the gauche rotamer more stable by 267 ± 57 cm −1 (763 ± 163 cal mol −1 ). The gauche to gauche, gauche to syn, and syn to gauche barriers have been determined to be 518, 839, and 572 cm −1 , respectively. Similarly, the barrier governing internal rotation of the CH 3 group has also been determined from the far-infrared spectrum of the gas. All of these data are compared with the corresponding quantities obtained from ab initio Hartree—Fock gradient calculations employing the RHF/3-21G * , RHF/6-31G * and MP2/6-31G * basis sets. Additionally, complete equilibrium geometries have been determined for both rotamers. The results are discussed and compared with the corresponding quantities for some similar molecules.

Raman (3200–10 cm−1) and infrared (3200–20 cm−1) spectra were recorded for the fluid and solid phases of trans-1-bromobut-2-ene (crotyl bromide), trans-CH3CHCHCH2BR, and a complete vibrational assignment is proposed. The fundamental asymmetric torsion for the more stable gauche conformer was observed in the far-infrared spectrum of the gas as a hybrid band centered at 75.0 cm−1. The enthalpy difference between the gauche and syn conformers is estimated to be 434 ± 111 cm−1 (1.24 ± 0.32 kcal mol−1) in the gas phase from the relative intensities of the Raman lines utilizing the differences in the Raman activities from the ab initio calculations with the RHF/STO-3G* basis set. The enthalpy difference was determined experimentally for the liquid from the relative intensities of the C–Br stretches as a function of temperature. The determined value is 370 ± 77 cm−1 (1.06 ± 0.22 kcal mol−1) with the gauche conformer the more stable form. A reasonable range of values was obtained for the coefficients of the potential function governing internal rotation about the CC bond. The three-fold barrier governing internal rotation of the CH3 group was determined from the far-infrared spectrum of the gas. All of these data are compared to the corresponding quantities obtained from ab initio Hartree–Fock gradient calculations employing the RHF/STO-3G* and RHF/LANL1DZ basis sets. Additionally, complete equilibrium geometries were determined for both rotamers. The results are discussed and compared with the corresponding quantities for some similar molecules.

The infrared spectra (4000–50 cm −1 ) of gaseous and solid divinylmethoxyborane, (CH 2 =CH) 2 BOCH 3 , as well as the Raman spectra (3500–20 cm −1 ) of the liquid and solid have been recorded. Qualitative depolarization values have been obtained from the Raman spectrum of the liquid. All normal modes, except the torsions, have been assigned based on infrared band contours, depolarization values, group frequencies, and normal coordinate calculations. From a comparison of the spectra in the fluid and solid states, it is concluded that the molecule exists predominantly in a single conformation in all physical states. Frequencies and potential energy distributions for the normal modes have been calculated with the 3–21G basis set. A comparison of these calculated frequencies to the observed spectra is consistent with the predominant form having a “planar” heavy atom skeleton with C s , symmetry. From the variable low temperature 13 C NMR data, a barrier to rotation about the B-O bond of 10.1 ± 0.1 kcal mol −1 has been determined, which is in excellent agreement with a barrier of 8.5 kcal mol"1 obtained from ab initio calculations. Structural parameters, conformational stability, and barriers to internal rotation have been obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21G and 6–31G * basis sets. The results are compared to the corresponding data for some similar organoboranes.

The gas-phase absolute IR absorption intensities for methylethyl ether and diethyl ether are determined. RHF/6-31G** ab initio calculations and experimental intensities for methylethyl ether are used to derive a set of local intensity parameters for methyl, methylene and skeletal vibrations of CH 3 OCH 2 CH 3 . These quantities are then used to predict quantitatively the absolute IR intensities of diethyl ether. The agreement between observed and calculated intensities is quite satisfactory.

The far-IR spectrum from 375 to 30 cm −1 of gaseous 3-chloro-2-methylpropene, CH 2 =C(CH 3 )CH 2 Cl, has been recorded at a resolution of 0.10 cm −1 . The fundamental asymmetric torsional mode for the gauche conformer is observed at 84.3 cm −1 with three excited states falling to lower frequency. For the higher energy s-cis conformer, where the chlorine atom eclipses the double bond, the asymmetric torsion is observed at 81.3 cm −1 with two excited states falling to lower frequency. Utilizing the s-cis and gauche torsional frequencies, the gauche dihedral angle and the enthalpy difference between conformers, the potential function governing the interconversion of the rotamers has been calculated. The determined potential function coefficients are (in reciprocal centimeters): V 1 =189±12, V 2 =−358±11, V 3 =886±2 and V 4 =−12±2 with an enthalpy difference between the more stable gauche and s-cis conformers of 150 ±25 cm −1 (430 ± 71 cal mol −1 ). This function gives values of 661 cm −1 (1.89 kcal mol −1 ), 1226 cm −1 (3.51 kcal mol −1 ) and 812 cm −1 (2.32 kcal mol −1 ), for the s-cis to gauche, gauche to gauche , and gauche to s-cis barriers, respectively. From the methyl torsional frequency of 170 cm −1 for the gauche conformer, the threefold barrier of 678 cm −1 (1.94 kcal mol −1 ) has been calculated. The asymmetric potential function, conformational energy difference and optimized geometries of both conformers have also been obtained from ab initio calculations with both the 3–21G * and 6–31G * basis sets. A normal-coordinate analysis has also been performed with a force field determined from the 3–21G * basis set. These data are compared with the corresponding data for some similar molecules.

The infrared (3200–50 cm −1 ) and Raman (3200–10 cm −1 ) spectra of gaseous and solid ethyl chlorosilane (CH 3 CH 2 SiH 2 Cl) have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Both the gauche and trans conformers have been identified in the vibrational spectra of the fluid phases, but only the gauche conformer remains in the solid. From the far infrared spectrum of the gas, the fundamental torsion for the gauche conformer has been observed at 79.1 cm −1 . A variable temperature study of the Raman spectrum of the liquid was carried out and the enthalpy difference was found to be 204 ± 23 cm −1 (583 ± 66 cal mol −1 ), with the gauche conformer being the more stable form. A complete vibrational assignment is proposed based on infrared band contours, depolarization ratios, and group frequencies. The assignment is supported by ab initio calculations using the RHF/3-21G* basis set to obtain the force constants and potential energy distribution. It is shown that the earlier reported r0 carbon-hydrogen distances were in error and revised r 0 structural parameters are proposed. Additionally, ab initio calculations have been carried out utilizing the RHF/3-21G * , RHF/6-31G * and/or MP2/6-31G * basis sets, from which the conformational stability, barrier to internal rotation, and optimized structural parameters have been obtained. The results of this study are compared to corresponding results of some related molecules.

The Raman (3100–10 cm−1) and infrared (3100–30 cm−1) spectra of difluoroacetyl chloride, CHF2CClO, in the gas and solid phases have been recorded. Additionally, the Raman spectrum of the liquid with qualitative depolarization ratios has been obtained. From these data, a trans/gauche equilibrium is proposed in the gas and liquid phases, with the trans conformer (hydrogen atom eclipsing the oxygen atom and trans to the chlorine atom) the more stable form in the gas, but the gauche rotamer is more stable in the liquid and is the only form present in the annealed solid. From the study of the Raman spectrum of the gas at different temperatures, a value of 272 ± 115 cm−1 (778 ± 329 cal mol−1) was determined for ΔH, with the trans conformer the more stable form. Similar studies were carried out on the liquid and a value of 109 ± 9 cm−1 (312 ± 26 cal mol−1) was obtained for ΔH, but now the gauche conformer is the more stable form. A potential function for the conformational interchange has been determined with the following potential constants: V1 = 397 ± 23, V2 = −101 ± 5, V3 = 474 ± 3, V4 = −50 ± 3, and V6 = 10 ± 2 cm−1. This potential has the trans rotamer more stable by 179 ± 31 cm−1 (512 ± 89 cal mol−1) than the gauche conformer. A complete vibrational assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group frequencies and normal coordinate calculations. The experimental conformational stability, barriers to internal rotation, and fundamental vibrational frequencies are compared with those obtained from ab initio Hartree-Fock gradient calculations employing both the RHF/3-21G* and RHF/6-31G* basis sets, and to the corresponding quantities obtained for some similar molecules.

The microwave spectrum of 1-fiuoro-2-methylpropane (isobutyl fluoride), (CH 3 )CHGH 2 , has been investigated in the region from 18.0 to 38.5 GHz. The a -type R -branch transitions have been assigned on the basis of the rigid rotor model. For the ground vibrational state the rotational constants were found to be A = 7631.03±0.14, B = 3480.96±0.01, and C =2633.38±0.01 MHz. The dipole moment components were determined from the Stark effect to be | μ a | = 1.702±0.002, | μ b | = 0.540|+-0.045, | μ c | = 0.296±0.007, and | μ t | = 1.810±0.003 D. These data clearly indicate that the assigned microwave spectrum is that of the gauche conformer. The IR (3500–40 cm −1 ) and Raman (3500–20 cm −1 ) spectra of the gas and solid have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Both the trans and gauche conformers have been identified in the vibrational spectrum of the fluid phases. From temperature studies of the Raman spectra of the gas and liquid, the enthalpy differences between the trans and gauche conformers were determined to be 154±38 cm −1 (440±109cal/mol) and 157±19 cm −1 (449±54cal/mol), respectively, with the gauche conformer being thermodynamically preferred in both phases. Upon crystallization only the gauche conformer remains in the solid state. Complete equilibrium geometries have been determined for both rotamers by ab initio Hartree-Fock gradient calculations employing RHF/3-21G, RHF/6-31G * and MP2/6-31G * basis sets. The normal modes and potential surface calculations have been carried out employing the RHF/6-31G * basis set. These results are discussed and compared to those obtained for some similar molecules.

The Raman spectra (3500–20 cm−1) of gaseous, liquid and solid and the infrared spectra (4000–50 cm−1) of gaseous and solid trimethoxyborane, B(OCH)3, were recorded. Qualitative depolarization values were obtained from the Raman spectrum of the liquid. All normal modes, except the torsions, were assigned based on infrared band contours, depolarization values, group frequencies and normal coordinate calculations. From a comparison of the spectra in the fluid states with that from the solid, it is concluded that the molecule exists predominantly in a single conformation in all physical states. Frequencies and potential energy distributions for the normal modes were calculated with the force constants obtained from ab initio calculations with the 3–21G basis set. A comparison of these calculated frequencies with the observed spectra is consistent with the predominant form having a ‘planar’ heavy atom skeleton with C3h symmetry. In was not possible to determine an experimental barrier to rotation about the BO bond. No change was observed in the 13C NMR spectrum over the temperature range of 22 to −90°C. Structural parameters, conformational stability and barriers to internal rotation were obtained from ab initio Hartree–Fock gradient calculations employing both the 3–21G and 6–31G* basis sets. The results are compared with the corresponding data for some similar organoboranes.

The IR (3200–30 cm−1) spectra have been recorded for S-methyl-N,N-dimefhylthiocarbamate, (CH3)2NC(O)SCH3, and its isotopomers, S-d3, N-d6 and N-d9, for the gas and liquid. Additionally, the Raman spectra (3200–10 cm−1) for the solid and liquid, with qualitative depolarization ratios, have been obtained for all the isotopes. These data are interpreted on the basis that the s-cis conformer (the S-methyl group oriented eis to the carbonyl group) with Cs symmetry is the only form existing in all three phases for this molecule. A complete vibrational assignment proposed for the -d0 molecule is facilitated by the availability of spectral data for five different isotopomers. A normal coordinate analysis has been carried out utilizing ab initio calculations with the 3–21G* basis set. The potential energy distributions and ab initio calculated frequencies have allowed a clarification of some of the corresponding results obtained from experiment. Structural optimizations and potential surface scan have also been carried out by ab initio calculations with the 3–21G* basis set. These results are compared with some previous studies on this molecule as well as on similar molecules.

The IR (3500–50 cm −1 ) and Raman (3500–20 cm −1 ) spectra of gaseous and solid cyclopropylmethylsilane, c -C 3 H 5 -CH 2 SiH 3 , have been recorded. Additionally, we have obtained the Raman spectrum of the liquid and the IR spectrum of the sample trapped in an argon matrix. From these data a complete assignment of the normal vibrational modes is provided. The spectra of the gaseous and liquid phases have been interpreted on the basis of the predominance of a conformation having a gauche structure and this form exists exclusively in the solid. Ab initio Hartree-Fock structural optimizations with the 3–21G* and 6–31G* basis sets are consistent with the gauche rotamer lying ~800 cm −1 lower in energy than the cis conformation which has the SiH3 group eis to the cyclopropyl ring. The force fields obtained with the 3–21G* basis set have been used to perforin a normal coordinate analysis. The cyclopropyl torsion has been observed as an IR band of hybrid contour centered at 80 cm −1 in the far-IR spectrum of the gas. Combination band spectra in the 2300–2000 cm −1 region of the mid-IR spectrum of the gas can be attributed to sum and difference bands of the SiH3 and cyclopropyl torsional modes with an SiH3 stretching mode. Analysis of these data leads to a barrier governing internal rotation of the silyl group of 687±50 cm −1 . These results are compared with corresponding quantities in some similar molecules.

The microwave spectra of two isotopic species of 2,2-difluoropropane, (CH 3 ) 2 13 CF 2 and (CD 3 ) 2 12 CF 2 , have been recorded from 26.5 to 40.0 GHz and the b -type R -branch transitions have been observed and assigned for the ground state. Utilizing the rotational transitions for these two isotopomers along with those for the normal species the following r o structural parameters have been determined: r (C-H) = 1.091±0.002A, r (C-C) = 1.510 + 0.005 A, r (C-F) = 1.378±0.005 A, ∢CCH = 109.26±0.05°, ∢CCC = 116.44±0.54° and ∢FCF = 105.15±0.50°. The carbon-hydrogen distances have also been obtained from the frequency of the isolated carbon-hydrogen frequency in the IR spectrum. The far-IR spectra of 2,2-difluoropropane- d 0 and - d 6 in the gas were recorded at a resolution of 0.10 cm −1 and the torsional fundamentals, along with several hot band transitions, have been assigned. From these data the barrier to internal rotation of the coupled rotors is 1103±48cm −1 (3.15±0.14kcalmol −1 ). The IR spectra (3600–50cm −1 ) of gaseous and solid and the Raman spectra (3600–10 cm −1 ) of gaseous, liquid and solid (CD 3 ) 2 CF 2 have been recorded. A complete vibrational assignment is proposed for both the normal and d 6 molecules based on depolarization values, relative intensities, isotopic shifts and normal coordinate calculations. The structural parameters, barriers to internal rotation and fundamental vibrational frequencies which have been determined experimentally are compared with those obtained from ab initio Hartree-Fock gradient calculations utilizing both the 3–21G and 6–31G* basis sets along with electron correlation at the MP2 level, and to the corresponding quantities obtained for some similar 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 microwave spectrum of N‐bromocyanofluoromethanimine CF(CN)NBr in the ground vibrational state in the region from 18.0 to 38.0 GHz has been investigated. The assigned spectrum is only consistent with a planar molecule with the cyano group trans to the bromine atom. The hyperfine structure due to the nuclear quadrupole coupling of the bromine nucleus has been analyzed for the a‐type R transitions of both the 81Br and 79Br isotopic species. Quadrupole splittings due to the 14N nuclei were not resolved. The rotational constants, the centrifugal distortion constant ΔJ, and the nonzero values of the diagonal and off‐diagonal elements of the bromine quadrupole coupling tensor were determined by a least‐squares fit for both isotopic species of bromine. The r0 structural parameters r(C–C), r(C–F), and ∢(N=C–C) were determined to have values of 1.422(9) and 1.349(15) A, and 121.6(9)°, respectively, whereas other structural parameters were fixed at the values obtained for the corresponding parameters of similar ...

The Raman (3200 to 10 cm−1) and infrared (3500 to 50 cm−1) spectra of vinyl chloroformate, H2C=CHOC(O)Cl, have been recorded for both the gas and solid. Additionally, the Raman spectrum of the liquid has been recorded, and depolarization ratios have been obtained. These data have been interpreted on the basis that the only stable conformation present at ambient temperature is thetrans-trans rotamer, where the firsttrans refers to the vinyl moiety relative to the O—CCl bond and the second to the C—Cl bond relative to the=C—O bond. Using harmonic rigid asymmetric top calculations, the infrared vapor phase contours for the C=O and the C=C stretch were predicted for thetrans-trans and for thecis-trans conformer, and were compared with experiment. For both fundamentals thetrans-trans hybrid reproduces the experimental contour, whereas thecis-trans contours fail to do so for both fundamentals. From far-infrared spectrum of the vapor obtained at 0.1 cm−1 resolution, the C(O)Cl andO-vinyl torsional fundamentals have been observed at 132 and 61 cm−1, respectively. Ther0 structural parameters have been obtained from a combination of ab initio calculated parameters with appropriate offset values and the fit of the microwave rotational constants for the two naturally occurring chlorine isotopes. The structure, barrier to internal rotation, and vibrational frequencies have been determined from ab initio Hartree-Fock gradient calculations, using the 3-21G* and 6-31G* basis sets. These results are compared to those obtained experimentally and to similar quantities for some related molecules.

The Raman (3500–10 cm−1) and infrared (3200–50 cm−1) spectra were recorded for the fluid and solid phases of but-2-enoyl chloride (crotonyl chloride), trans-CH3CHCHCClO, where the methyl group is trans to the CClO group, and a complete vibrational assignment is proposed. These data were interpreted on the basis that the s-trans (anti) form (two double bonds oriented trans to one another) is the most stable form in the fluid phases and the only conformer remaining in the solid state. The asymmetric torsional fundamental of the more stable s-trans and the higher energy s-cis (syn) form were observed at 97.5 and 86.9 cm−1, respectively. From these data the asymmetric potential function governing the internal rotation about the CC bond was determined. The potential coefficients are V1 = −111 ± 2, V2 = 1860 ± 48, V3 = 6 ± 2, V4, = −43 ± 24 and V6 = −22 ± 6. The s-trans to s-cis and s-cis to s-trans barriers were determined to be 1890 and 1785 cm−1, respectively, with an enthalpy difference between the conformers of 105 ± 52 cm−1 [300 ± 149 cal mol−1 (1 cal = 4.184 J)]. Similarly, the barrier governing internal rotation of the CH3 group for the s-trans conformer was also determined to be 912 ± 30 (2.61 ± 0.09 kcal mol−1) from the torsional fundamental observed in the far-infared spectrum of the gas. All these data were compared with the corresponding quantities obtained from ab initio Hartree–Fock gradient calculations employing the RHF/3–21G*, RHF/6–31G* and/or MP2/6–31G* basis sets. These results were compared with the corresponding quantities for some similar molecules.

Author Institution: Department of Chemistry and Biochemistry., University of South Carolina

Charcoal-rich zones in a peat core from the Snuggedy Swamp in South Carolina were investigated to determine the chemical and physical changes associated with fires. Petrographic analyses of microtome thin sections revealed that three charcoal zones were present in the core and that the fires causing such zones were severe enough to penetrate into the subsurface and burn some of the peat. Despite these severe fires, only minor changes in the botanical composition occurred throughout the history of the study site, suggesting that these fires were not extensive enough to retard recolonization of the site from nearby unburned areas. pyrolysis gas chromatography/Fourier transform infrared/flame ionization detection and pyrolysis gas chromatography/mass spectrometry studies reveal distinct organic chemical changes in the peat that can be related to the fires. Decreases in aliphatic and cellulose compounds mirrored increases in charcoal abundance; while aromatic, lignin-related compounds increased as charcoal increased.

The Raman spectra of gaseous, liquid and solid 2,3-dichloropropene, CH2=C(CH2Cl)Cl and both trans and cis-1,3-dichloropropene, ClHC=CH(CH2Cl) have been recorded. For the first two molecules both the anticlinal (gauche) and synclinal (s-cis) conformers have been observed in the fluid states at ambient temperature whereas for the latter molecule only the anticlinal conformer is present in all three physical states. Conformational stabilities have been determined from the temperature dependence of the Raman spectrum.

From a combination of infrared and Raman spectral data and ab initio calculations, the conformational stabilities have been determined for the difluoroacetyl halides in vapor, liquid and solid phases.

The infrared and Raman spectra of gaseous, liquid and solid fluorocarbonyl isocyanate, FC(O)NCO, and acetyl isocyanate, CH 3 C(O)NCO, have been recorded. From these data the conformational stability has been determined for both molecules for all three physical states. The conformational energy differences, optimized geometries, and fundamental vibrational frequencies have also been obtained from ab initio calculations.

From a combination of the Raman spectral data and ab initio calculations, the relative conformational stabilities have been determined for the oxalyl halides in both the gaseous and liquid states.

Vibrational spectra (3500 to 50 cm −1 ) of gaseous, liquid and solid and the samples trapped in an Ar matrix of cyclopropylmethylsilane, c-C 3 H 5 -CH 2 SiH 3 , and cyclopropylmethyltrifluorosilane, c-C 3 H 5 -CH 2 SiF 3 , have been recorded. The spectra of the gaseous and liquid phases have been interpreted on the basis of the predominance of a conformation having a gauche structure (>90%) and this form exists exclusively in the solid. Only for cyclopropylmethyltrifluorosilane was there evidence for a second conformer.

With the availability of fast and relatively cheap computer workstations, it is now possible to carry out rapid ab initio calculations on molecules with twelve or more atoms with the 3-21G basis set. These data can be very valuable in vibrational assignments, conformational analyses, and structural determinations. Ab initio calculations also contribute significantly in the area of vibrational frequencies and harmonic force constants.

The Raman spectra (3400-10 cm −1 ) of liquid and solid 3-methyl-3-vinylcyclopropene, C 3 H 2 (CH 3 )CHCH 2 , and its isotopomer C 3 D 2 (CH 3 )CHCH 2 were recorded. The temperature dependence of some band intensities and qualitative depolarization ratios show that the thermodynamically preferred conformation is s-trans. The structural parameters and conformational stability of s-trans and gauche rotamers were obtained from ab initio calculations by employing both 3-21G and 6-31G* basis sets. Barriers to internal rotation and fundamental vibrational frequencies were calculated utilizing the 3-21G basis set. The ab initio results are consistent with the experimentally indicated greater stability of the s-trans relative to the gauche conformer

The Raman (1800–10 cm−1) and infrared (2000–30 cm−1) spectra of bromodifluoroacetyl chloride, CBrF2CClO, are reported for the gas and polycrystalline solid. Additionally, the Raman spectrum of the liquid along with qualitative depolarization ratios have also been obtained. These data have been interpreted on the basis of an equilibrium between the gauche and the trans conformers (bromine atom trans to the chlorine atom) in the gas and liquid phases. From a study of the Raman spectrum of the liquid at various temperatures, a value of 851 ± 56 cm−1 (2.43 ± 0.07 kcal mol−1) was obtained for ΔH with the gauche conformer the more stable form. A similar study of the gas gave a value of 725 ± 150 cm−1 (2.07 ± 0.43 kcal mol−1), again with the gauche rotamer the more stable conformer. Hence the gauche conformer is the predominate rotamer in the gas and liquid and the only conformer present in the annealed solid. Aided by ab initio and scaled computations of the vibrational spectrum with the STO-3G* basis set and, for the trans conformer at the 4–31G*/MIDI-4* level of the theory, complete assignments of observed bands to fundamental vibrations of the gauche conformer are made, whereas partial assignment is reported for the trans conformer. The fundamental torsional mode for the gauche conformer was observed at 46 cm−1 but excited-state transitions were not observed so the potential function governing the conformational interchange could not be determined. Optimized geometries, dipole moments, unscaled and scaled vibrational frequencies and harmonic force fields are reported for both conformers. With the STO-3G*, basis set, the gauche conformer is calculated to be more stable than the trans conformer by 17 cm−1 (48 cal mole−1). These results are compared with the corresponding quantities for some similar molecules.

The infrared (4000-50 cm−1) and Raman spectra (3500-10 cm−1) have been recorded for dimethylmethoxyborane, (CH3)2BOCH3, in both the gaseous and solid states. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Only one conformation has been found in all three physical states and, on the basis of the polarized nature of the Raman band assigned as the BC2 antisymmetric stretch, this conformer is identified as being the “planar” form with Cs molecular symmetry. A complete vibrational assignment is proposed based on the depolarization data, infrared gas phase band contours, and group frequencies. Additionally, variable temperature 13C NMR studies have been carried out and the barrier to rotation about the BO bond has been determined as 8.9 kcal mol−1. Structural parameters have been obtained from ab initio Hartree—Fock gradient calculations employing 3-21G and 6-31G* basis sets. The results are compared with the rα values obtained earlier from an electron-diffraction study. Potential-surface calculations have been carried out to determine the conformational stability and barriers to internal rotation. Frequencies and potential-energy distributions for the normal modes have been calculated utilizing the 3-21G basis set. All results are compared to the corresponding data for some other organoboranes.

The microwave spectrum of chlorocyclopentane has been reinvestigated. The ground state and two vibrationally excited states of the equatorial conformation of c‐C5H935Cl have been identified. The ground state rotational constants are A=6424.51(14) MHz, B=1832.304(6) MHz, C=1523.163(5) MHz. The spectrum of the 37Cl substituted species has also been assigned. For the previously reported axial conformer of c‐C5H935Cl, additional transitions have been measured in the ground state and the first excited state of the lowest frequency motion and the spectrum of another vibrationally excited state has been assigned. The experimental rotational constants have been used to derive plausible molecular structures for both conformers. The experimental quadrupole coupling constants are compatible with the proposed structures.

The far-IR (370-50 cm −1 ) spectra of gaseous ethanol, CH 3 CH 2 OH, and the O- d compound have been recorded at a resolution of 0.10 cm −1 . Similar far-IR spectra have been collected for 2,2,2-trifluoroethanol, CF 3 CH 2 OH, and the O- d , C- d 2 and - d 3 isotopic species. In addition, the Raman (4000-50 cm −1 ) and the mid-IR (5000-400 cm −1 ) spectra have been collected for CF 3 CH 2 OH and the isotopic compounds in the vapor phase. A detailed examination of the torsional modes has been carried out and potential functions for the hindered internal rotation of the OH and OD groups and the CH 3 and CF 3 rotors are calculated. For ethanol, the fundamental OH torsion for the trans conformer is observed at 202.6 cm −1 whereas for the gauche conformation, the 1 −1 ← 0 + transition is found at 243.1 cm −1 and the 1 + ← 0 − transition is 195.8 cm −1 . An asymmetric potential function utilizing these transitions gives values of 403 cm −1 (1.15 kcal mol −1 ) for the trans/gauche barrier and 399 cm −1 (1.14 kcal mol −1 ) for the gauche/gauche barrier with the trans conformer more stable by 42 cm −1 (120 cal mol −1 ) than the gauche conformer. Potential functions for the hydroxy torsions are also calculated for the ethanol O- d compound and the four 2,2,2-trifluoroethanol isotopic molecules. The CH 3 torsional transitions of trans ethanol give a V 3 barrier of 1185 ± 16 cm −1 (3.39±0.05 kcal mol −1 ) and the corresponding barrier for the gauche conformer is 1251±2 cm −1 (3.58±0.01 kcal mol −1 ). Similarly, a series of CF 3 torsional transitions was observed for the trans and gauche conformations of the CF 3 CH 2 OH molecule as well as for some of the isotopic species. In addition to the examination of the far-IR spectra, a series of sum and difference bands associated with the OH and OD stretching fundamentals is found in the mid-IR spectra for the 2,2,2-trifluoroethanol compounds and a possible explanation for these modes is given.

The far-IR spectrum (350-35 cm −1 ) of gaseous 1 -bromo-2-fluoroethane, BrCH 2 CH 2 F, has been recorded at a resolution of 0.10 cm − 1. The fundamental asymmetric torsional frequencies of the more stable trans (two halogen atoms oriented trans) and high energy gauche conformers have been observed at 125.3 cm −1 and 111.3 cm −1 , respectively, and the asymmetric torsional potential function governing internal rotation about the CC bond has been determined. This potential function gives values for the torsional potential coefficients of V 1 =584±6, V 2 =-147±4, V 3 =1217±11, V 4 =138±2, and V 4 = −21+4 cm −1 , and a dihedral angle (∠FCCBr) of 67°0 for the gauche conformer. The trans to gauche, gauche to gauche, and gauche to trans barriers have been determined to be 1356 cm −1 , 1418 cm −1 and 973 cm −1 , respectively, with an energy difference between the conformations of 383±21 cm −1 (1.09±10.06 kcal mol −1 ). From studies of the Raman spectra at variable temperatures the conformational energy difference has been determined to be 350 ± 87 cm −1 (1.00±0.25 kcal mol −1 ) with the trans more stable and 300±46cm −1 (0.86±0.13 kcal mol −1 ) with the gauche more stable for the gas and liquid, respectively. A complete assignment of the vibrational spectra including the IR (3500-400 cm') spectra of the gas and solid and the Raman (3200-10 cm −1 ) spectra of the gas, liquid and solid is proposed. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental vibrational frequencies which have been determined from experiment, are compared to those obtained from ab initio Hartree-Fock gradient calculations and to the corresponding quantities obtained for some similar molecules.

The microwave spectra of two isotopic species of trimethylphosphine, (CD 3 ) 2 (CH 3 )P and (CD 3 ) 3 P, have been recorded in the spectral region 20–39 GHz. Only c-type transitions were observed and R -branch assignments have been made for the (CD 3 ) 2 (CH 3 )P molecule and two transitions were observed for the symmetric top molecule, (CD 3 ) 3 P. From these rotational constants along with those reported for five other isotopic species of trimethylphosphine, the complete r 0 structural parameters have been determined and they are: r (PC = 1.845±0.001A, r(CH) = 1.096±0.001 A, ∠CPC = 98.95 ± 0.20°, ∠HCH = 109.02±0.16° with an angle of tilt of the methyl groups of 1.67±0.17°. The Raman spectra (3500-100 cm −1 of (CD 3 )(CH 3 ) 2 P and (CD 3 ) 2 (CH 3 )P in the liquid state have been obtained. From these data, along with the vibrational data for the d 0 - and d 9 -molecules, a complete vibrational assignment is proposed. The fundamental vibrational frequencies, barriers to internal rotation and structural parameters which have been obtained experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G basis set. Additionally, structural parameters have been calculated utilizing 3-21G * ,6-31G ** and DZ basis sets. All to these results are compared to the corresponding quantities for some similar molecules.

The Raman spectra (3600-10 cm −1 ) of gaseous, liquid and solid and the infrared spectra (3600- 40 cm −1 ) of gaseous and solid 2-methylpropanal (isobutyraldehyde), (CH 3 ) 2 CHCHO, and the corresponding deuterium compound (CD 3 ) 2 CDCHO have been recorded. Additionally, qualita- tive depolarization ratios have been obtained from the Raman spectra of the liquids. These data have been interpreted for the fluid phases, showing that the gauche conformation (oxygen atom eclipsing a methyl group) is thermodynamically preferred over the high energy trans conformation (oxygen atom eclipsing the secondary hydrogen) and is the only rotamer present in the spectra of the annealed solids. From the relative intensities of the Raman lines of the liquid at 633 cm −1 (gauche) and 551 cm −1 (trans) as a function of temperature, the enthalpy difference is found to be 440±17 cm −1 (1.26±0.05 kcal mol −1 ). Utilizing rotational constants from previously reported microwave data and structural parameters obtained from ab initio calculations, the r 0 structural parameters are reported for both rotameric forms. The ab initio and r 0 structures for the gauche conformer are consistent with nonequivalent CC bond distances for the isopropyl moiety. A complete vibrational assignment is proposed which is based on infrared band contours, depolarization values, isotopic shifts and group frequencies. 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 Hartree-Fock gradient calculations utilizing both the 3-21G and 6-31G* basis sets, and to the corresponding quantities obtained for some similar molecules.

The far infrared (50-370-cm -1 ) and low frequency Raman (70-300-cm -1 ) spectra of gaseous 1,2-difluoroethane have been recorded. The fundamental asymmetric torsional frequencies of the more stable gauche (two fluorine atoms oriented gauche to one another) and the high energy trans conformations have been observed in the far infrared spectrum of the gas at 147.0 and 116.7 cm -1 , respectively. For the trans conformer, four Q-branches arising from transitions between excited torsional vibrational states have also been observed

The Raman (3200 to 10 cm−1) and infrared (3500 to 50 cm−1) spectra of vinyl chloroformate, H2C=CHOC(O)Cl, have been recorded for both the gas and solid. Additionally, the Raman spectrum of the liquid has been recorded, and depolarization ratios have been obtained. These data have been interpreted on the basis that the only stable conformation present at ambient temperature is thetrans-trans rotamer, where the firsttrans refers to the vinyl moiety relative to the O—CCl bond and the second to the C—Cl bond relative to the=C—O bond. Using harmonic rigid asymmetric top calculations, the infrared vapor phase contours for the C=O and the C=C stretch were predicted for thetrans-trans and for thecis-trans conformer, and were compared with experiment. For both fundamentals thetrans-trans hybrid reproduces the experimental contour, whereas thecis-trans contours fail to do so for both fundamentals. From far-infrared spectrum of the vapor obtained at 0.1 cm−1 resolution, the C(O)Cl andO-vinyl torsional fundamentals have been observed at 132 and 61 cm−1, respectively. Ther0 structural parameters have been obtained from a combination of ab initio calculated parameters with appropriate offset values and the fit of the microwave rotational constants for the two naturally occurring chlorine isotopes. The structure, barrier to internal rotation, and vibrational frequencies have been determined from ab initio Hartree-Fock gradient calculations, using the 3-21G* and 6-31G* basis sets. These results are compared to those obtained experimentally and to similar quantities for some related molecules.

Raman (3200 to 10 cm −1 ) and infrared (3200 to 50 cm −1 ) spectra have been recorded for the fluid and solid phases of trans -1-chloro-2-butene (crotyl chloride, trans -CH 3 CHCHCH 2 Cl), and a complete vibrational assignment is proposed. The fundamental asymmetric torsion for the more stable gauche conformer has been observed in the far infrared spectrum of the gas and has a hybrid contour centered at 82.5 cm −1 . The corresponding mode for the syn conformer (allylic chlorine atom oriented syn to the double bond) gives rise to a series of well defined C -type Q -branches beginning at 110.7 cm −1 and proceeding to lower frequencies. From these data the potential function governing internal rotation of the asymmetric top has been determined and the following potential coefficients have been obtained: V 1 = −371 ± 18, V 2 = −103 ± 9, V 3 = 662 − 30, V 4 = 123 ± 5, V 6 = −20 ± 12 cm −1 . This potential function has the gauche rotamer more stable by 267 ± 57 cm −1 (763 ± 163 cal mol −1 ). The gauche to gauche, gauche to syn, and syn to gauche barriers have been determined to be 518, 839, and 572 cm −1 , respectively. Similarly, the barrier governing internal rotation of the CH 3 group has also been determined from the far-infrared spectrum of the gas. All of these data are compared with the corresponding quantities obtained from ab initio Hartree—Fock gradient calculations employing the RHF/3-21G * , RHF/6-31G * and MP2/6-31G * basis sets. Additionally, complete equilibrium geometries have been determined for both rotamers. The results are discussed and compared with the corresponding quantities 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.

Variable temperature (−55 to −131 °C) studies of the infrared spectra (4000–50 cm −1 ) of 2-fluoroethylamine, FCH 2 CH 2 NH 2 dissolved in liquid xenon and the far infrared in liquid krypton have been carried out. From these data all five possible conformers have been identified and their relative stabilities obtained. The enthalpy differences have been determined among the most stable Gg′ conformer and the second stable conformer, Gt, to be 62 ± 8 cm −1 (0.74 ± 0.10 kJ/mol), the third stable conformer, Tg, to be 262 ± 26 cm −1 (3.14 ± 0.3 kJ/mol), the fourth most stable conformer, Tt, to be 289 ± 45 cm −1 (3.46 ± 0.5 kJ/mol) and the fifth most stable conformer, Gg to be 520 ± 50 cm −1 (6.24 ± 0.6 kJ/mol). The percentage of each conformer at ambient temperature is estimated to be with Gg′ (42 ± 4%), Gt (32 ± 1%), Tg (13 ± 1%), Tt (5 ± 1%) and Gg (3 ± 1%). The first indicator is the NCCF dihedral angle (G = gauche or T = trans ) and the second one (g = gauche or t = trans ) is the relative position of the lone pair of electrons on the nitrogen atom with respect to the fluorine atom. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug-cc-pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. By utilizing previously reported microwave 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 two most stable conformers. The determined heavy atom structural parameters for the Gg′[Gt] conformer are: the distances (A) C 1 –C 2 = 1.509(3) [1.516(3)], C 2 –N 3 = 1.466(3)[1.461(3)], C 1 –F 4 = 1.400(3)[1.398(3)] and angles in degrees ∠N 3 C 2 C 1 = 109.8(5) [115.5(5)], ∠F 4 C 1 C 2 = 109.2(5)[109.3(5)], ∠H 10 N 3 H 9 = 107.1(5) [107.1(5)](°) and τ F 4 C 1 C 2 N 3 = 65.3(5) [60.9(5)]. Vibrational assignments have been provided for most of the observed bands which have been supported by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force fields, frequencies, infrared intensities, Raman activities and depolarization ratios for all five conformers. The results are discussed and compared to the corresponding properties of some similar molecules.

The asymmetric torsional potential function, conformational energy difference, vibrational frequencies, and structural parameters of Cyclopropane-carboxaldehyde have been obtained from ab initio calculations at the 3–21G and/or 6-31G* baiss set levels. These results have allowed for a reinterpretation or clarification of some of the corresponding results obtained from experiment. The conformations that have the oxygen atom oriented cis and trans to the three-membered ring are observed and calculated to be the most stable and high energy forms in the gaseous phase, respectively. From the ab initio calculations using the 6–31 G* basis set, the energy difference between the two conformers is 114 cm−1. For the liquid, the trans conformer is more stable and is the only rotamer present in the annealed solid. Based on a combination of results obtained from ab initio calculations, microwave spectroscopy, and the electron diffraction technique,r o structural parameters have been obtained for both conformations.

The Raman spectra (3200—10 cm−1) of gaseous, liquid and solid and infrared spectra (3200—40 cm−1) of gaseous and solid 3-iodopropene, H2CCHCH2I, were recorded. The fundamental asymmetric torsional transition of the most stable gauche conformer was observed in the Raman and far-infrared spectra of the gas at 95 cm −1. In the Raman spectrum of the liquid a second CI stretch and two skeletal bending modes were identified for the less stable cis conformer. From a study of the Raman spectrum of the liquid at various temperatures, a value of 648±81 cm−1 (1.85±0.23 kcal mol−1)was determined for the enthalpy difference between the higher energy cis and preferred gauche conformers. These data, along with the dihedral angle for the gauche conformer obtained from an electron diffraction study, combined with results obtained from ab initio calculations, allow for an estimate of the potential function governing internal rotation about the CC bond. The values for the torsional potential coefficients are V1 = −208 ± 10, V2 = −532 ± 10, and V3 = 534 ± 8 cm−1. This potential is consistent with a dihedral angle (∠ CCCI) of 113.0° for the gauche conformer cis to gauche, gauche to gauche and gauche to cis barriers of 160, 904 and 738 cm−1, respectively, and an enthalpy difference between the conformers of 580 ± 30 cm−1 (1.66 ± 0.09 kcal mol−1). The asymmetric torsional potential surface, complete equilibrium geometries and vibrational frequencies were calculated using restricted Hartree-Fock calculations with the STO-3G*, 3-21G*/medium, a medium-sized combination basis set suitable for a DZ-type contraction of the valence shell orbitals, and the LANL1DZ basis sets. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.

The far infrared spectrum (375 to 30 cm−1) of gaseous 2-chloro-3-fluoropropene, CH2=C(CH2F)CI, has been recorded at a resolution of 0.10 cm−1. The fundamental asymmetric torsional mode is observed at 117.5 cm−1 with ten excited states falling to low frequency for thes-cis (fluorine atom eclipsing the double bond) conformer. For the higher energy gauche conformer, the asymmetric torsion is estimated to be at 94 cm−1. From these data the asymmetric torsional potential function has been calculated. The potential function coefficients are calculated to be in cm−1):V1=803±21,V2=−94±21,V3= 1025±10,V4=95±10, andV6=2±1, with an enthalpy difference between the more stables-cis and gauche conformera of 550±100 cm−1 (1.57±0.29 kcal/mol). This function gives values of 1227±50cm−1(3.51±0.14kcal/mol), 1266±200 cm−1 (3.62±0.57 kcal/mol), and 665±100 cm−1 (1.90±0.29 kcal/mol), for thes-cis to gauche, gauche to gauche, and gauche tos-cis barriers, respectively. From the relative intensities of the Raman lines of the gas at 652 cm−1 (gauche) and 731 cm−1 (s-cis) as a function temperature, the enthalpy difference is found to be 565±96 cm−1 (1.62±0.27 kcal/mol). However, the more polar gauche conformer remains in the crystalline solid. The Raman spectrum of the gas has been recorded from 3500 to 70 cm−1 and, utilizing these data and the previously reported infrared data, a complete vibrational analysis is proposed for both conformers. The conformational stability, barriers to internal rotation, fundamental vibrational frequencies, and structural parameters that have been determined experimentally are compared to those obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21 G* and 6–31G* basis sets and to the corresponding quantities for some similar molecules.

The Raman (3200 to 10 cm−1) and far infrared (380 to 60 cm−1) spectra of gaseous fluorocyclobutane,c-C4H7F, have been recorded. A series of Q-branches observed in both of these spectra beginning at 166 cm−1 with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fit to an asymmetric potential function of the form:V (cm−1)=(1.76±0.05)103X+(4.88±0.28)104X2+(2.12 ±0.16)103 exp(−5.66±0.41)10X2 with a reduced mass function ofg44= 0.00386−0.00295X+0.03485X2+0.1228X3 +0.3459X4, whereX is the ring puckering coordinate. Utilizing this potential, the difference between the puckering angles for the two conformers was calculated to be 4° with the equatorial conformer having the larger value of 28°. This potential function is consistent with an energy difference between the equatorial and axial forms of 447 cm−1 (1.28 kcal/mol) and a barrier to ring inversion from the equatorial to the axial conformation of 713 cm−1 (2.04 kcal/mol). Experimental values for the enthalpy difference between the two conformers have been determined for both the liquid (400±30 c−1) and gas (413±43 cm−1) from investigations of the Raman spectra at variable temperatures. The conformational stability, enthalpy difference, structural parameters, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G, 6-31 G*, and 6-31 G** basis sets.

The far infrared (50-370-cm -1 ) and low frequency Raman (70-300-cm -1 ) spectra of gaseous 1,2-difluoroethane have been recorded. The fundamental asymmetric torsional frequencies of the more stable gauche (two fluorine atoms oriented gauche to one another) and the high energy trans conformations have been observed in the far infrared spectrum of the gas at 147.0 and 116.7 cm -1 , respectively. For the trans conformer, four Q-branches arising from transitions between excited torsional vibrational states have also been observed

This report does a complete vibrational spectal analysis of 2-methylpropionyl fluoride using microwave, infrared, and Raman spectra.