Infrared and raman spectra,vibrational assignment and barriers to internal rotation for methyldisilylamine

The Raman spectra of gaseous and liquid (SiH₃)₂NCH₃ and (SiH₃)₂NCD₃ have been recorded to within 10 cm^?1 of the exciting line. The IR spectra of (SiH₃)₂NCH₃ and (SiH₃)₂NCD₃ have been recorded from 80 cm^?1 to 3800 cm^?1 in the gaseous state, and from 80 cm^?1 to 450 cm^?1 in the solid state. A vibrational assignment has been made, and from the low-frequency vibrational data, an upper limit of 3.3 kcal mol^?1 was calculated for the barrier to internal rotation of the silyi groups, whereas a barrier of ~450 cal was calculated for internal rotation of the methyl group. It is concluded that there exists a significantly strong d_π—p_π interaction in methyldisilylamine.     

Spectra and structure of silicon compounds. XVII Raman and infrared spectra and vibrational assignment for hexamethyldisilane and ab initio calculations for disilane and hexamethyldisilane

The IR spectra of gaseous and solid hexamethyldisilane between 4000 and 25 cm⁻¹ and the far-IR spectrum of the liquids from 450 to 25 cm⁻¹ have been recorded. The Raman spectra have been recorded from 3500 to 10 cm⁻¹ for all three physical phases. Assisted by ab initio calculations, the vibrational spectrum of hexamethyldisilane has been assigned under D_3d symmetry and the results of a normal coordinate analysis are discussed. No spectral features indicative of free internal rotation have been observed. Gradient ab initio calculations have been carried out for the disilane and hexamethyldisilane molecules using different types of basis sets. The structural parameters, rotational constants, unscaled and scaled frequencies and harmonic force constants have been reported for both disilane and hexamethyldisilane.     

Infrared and Raman spectra,conformational stability,barriers to internal rotation,ab initio calculations and vibrational assignment of ethyl methyl selenide

The Raman spectra (3200–10 cm⁻¹) of ethyl methyl selenide in the gas, liquid and solid phases and the infrared spectra (3200–30 cm⁻¹) of the gas and solid have been recorded. Qualitative depolarization ratios have been obtained for the lines in the Raman spectrum of the liquid. By a variable temperature Raman study of the liquid, it has been determined that the gauche conformer is more stable than the trans rotamer by 158±16 cm⁻¹ (452±46 cal mol⁻¹), and the gauche conformer is the rotamer present in the solid. A complete vibrational assignment for the gauche conformer is presented. All of these data are compared to the corresponding quantities obtained from ab initio Hartree—Fock gradient calculations employing the STO-3G* and 4–31G*/MIDI-4* basis sets. Complete equilibrium geometries have been calculated for both rotamers and the results are discussed and compared with the corresponding quantities for some similar molecules.     

Spectra and structure of gallium compounds: Part X. Infrared and Raman spectra,vibrational assignment,and normal coordinate calculations for trimethylaminegallium trichloride

The far IR (450–480 cm^?1) and Raman (3200–3230 cm^?1) spectra of (CH₃)₃ NGaCl₃ have been recorded in the solid state and interpreted in detail on the basis of C₃ molecular symmetry. A modified valence force field model is used to calculate the frequencies and potential energy distribution of the adduct. The calculated force constants of the adduct are compared with those previously reported for the free Lewis acid and the free Lewis base moieties, and the observed differences ascribed to geometrical changes of the uncomplexed species on adduct formation and explained on the basis of the VSEPR model and non-bond interactions. Extensive coupling is observed between the GaN stretching mode and the NC₃ symmetric stretching and the NC₃ symmetric deformational modes. Strong coupling interaction is also found between the GaCl₃ antisymmetric stretch and the NC₃ antisymmetric deformation. The calculated value of 2.50 mdyn Å^?1 for the GaN stretching force constant in (CH₃)₃NGaCl₃ is larger than any of those previously determined in complexes such as (CH₃)₃NGaH₃ (2.43 mdyn Å^?1), (CH₃)₃NGa(CH₃)₃ (1.61 mdyn Å^?1), and H₃NGa(CH₃)₃ (1.08 mdyn Å^?1). The observed variations in the magnitudes of the stretching force constants of the donor—acceptor dative bond is found to be consistent with the estimated relative stabilities of this series of adducts.     

Conformational analysis,barriers to internal rotation and vibrational assignment for dimethylethylamine

The IR (50–3500 cm^?1) and Raman (20–3500 cm^?1) spectra have been recorded for gaseous and solid dimethylethylamine. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Due to the fact that three distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phases with the gauche conformer being more stable and the only one present in the spectra of the unannealed solid. From the temperature study of the Raman spectrum of the liquid a rough estimate of 3.9 kcal mol^?1 has been obtained for ΔH. Relying mainly on group frequencies and relative intensities of the IR and Raman lines, a complete vibrational assignment is proposed for the gauche conformer. The potential functions for the three methyl rotors have been obtained, and the barriers to internal rotation for the two CH₃ rotors attached to the nitrogen atom have been calculated to be 3.51 and 3.43 kcal mol^?1, whereas the barrier for the CH₃ rotor of the ethyl group has been calculated to be 3.71 kcal mol^?1. The asymmetric torsional mode for the gauche conformer has been observed in both the IR and Raman spectra of the gas at 105 cm^?1 with at least one hot band at a lower frequency. Since the corresponding mode has not been observed for the trans conformer, it is not possible to obtain the potential function for the asymmetric rotation although estimates on the magnitudes of some of the terms have been made. Significant changes occur in the low-frequency IR and Raman spectra of the solid with repeated annealing; several possible reasons for these changes are discussed and one possible explanation is that a conformational change is taking place in the solid where the trans form is stabilized by crystal packing forces. These results are compared to the corresponding quantities for some similar amines.     

Infrared and Raman spectra, conformational stability, barriers to internal rotation, normal-coordinate calculations and vibrational assignments for vinyl silyl bromide

The infrared (3200-30 cm(-1) spectra of gaseous and solid, the Raman spectra (3200-30 cm(-1)) of the liquid and solid vinyl silyl bromide, CH2CHSiH2Br, have been recorded. Additionally, quantitative depolarization values have been obtained. Both the gauche and cis conformers have been identified in the fluid phases but only the gauche conformer remains in the solid. Variable temperature studies from 0 to -87 degrees C of the Raman spectrum of the liquid was carried out. From these data, the enthalpy difference has been determined to be 22 +/- 6 cm(-1) (0.26 +/- 0.08 kJ/mol), with the gauche conformer being the more stable form. The predictions from the ab initio calculations up to MP2/6-311 + + G(2d,2p) basis set favor the gauche as the more stable form. A complete vibrational assignment is proposed for both the gauche and cis conformers based on infrared band contours, relative intensities, depolarization values and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations and the potential energy terms for the conformer interconversion have been obtained from the same calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing a variety of basis sets up to 6-311 + + G(2d,2p) at levels of restricted Hartree-Fock (RHF) and/or Moller-Plesset (MP) to second order. The results are discussed and compared to those obtained for some similar molecules.     

Infrared and raman spectra,conformational stability,barriers to internal rotation,ab initio calculations and vibrational assignment of difluoroacetyl chloride

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.     

Spectra and structure of silicon-containing compounds. Part XXXVIII: Infrared and Raman spectra,vibrational assignment,conformational stability,and ab initio calculations of vinyldifluorosilane

Infrared spectra (3500-50 cm(-1)) of gaseous and solid, and Raman spectrum (3500-30 cm(-1)) of liquid vinyldifluorosilane, CH(2)z.dbnd6;CHSiF(2)H, are reported. Both the cis and gauche rotamers have been identified in the fluid phases. From temperature-dependent FT-infrared spectra of krypton solutions, it is shown that the cis conformer is more stable than the gauche form by 119+/-12 cm(-1) (1.42+/-0.14 kJ mol(-1)). At ambient temperature there is 53+/-2% of the gauche conformer present. Complete vibrational assignments are provided for the cis conformer and several modes are identified for the gauche form. Harmonic force constants, fundamental frequencies, infrared intensities, and Raman activities have been obtained from MP2/6-31G(d) calculations with full electron correlation. The optimized geometries and conformational stabilities have also been obtained from ab initio MP2/6-31G(d), MP2/6-311+G(d,p), and MP2/6-311+G(2d,2p) calculations with full electron correlation as well as from density functional theory calculations (DFT) by the B3LYP method. The SiH bond distances (r(0)) of 1.472 and 1.471 A have been obtained for the cis and gauche conformers, respectively, from the silicon-hydrogen stretching frequencies. These results are compared to the corresponding quantities of the corresponding carbon analogue as well as with some similar molecules.     

Spectra and structure of gallium compounds: Part VI. Infrared and Raman spectra of trimethylgalliumtrimethylphosphine

The infrared (50–4000 cm^?1 ) and Raman (50–3500 cm^?1) spectra of (CH₃)₃GaP(CH₃)₃ have been recorded for the solid state at the temperature of boiling liquid nitrogen. The spectra have been interpreted on the basis of C_3v molecular symmetry and a complete vibrational assignment except for the methyl torsional modes is presented. A modified valence force field model has been utilized in calculating the frequencies and potential energy distribution. The calculated potential constants for the adducts are compared to those previously reported for the Lewis acid and the Lewis base moieties and the differences are shown to be consistent with structural changes upon adduct formation. Extensive coupling has been observed between the Ga-P stretching mode and the PtC₃ and GaC₃ deformational modes. Substantial coupling is also observed between the PC₃ and the GaC₃ rocking motions. The magnitude of the Ga-P stretching force constant is found to be much smaller (0.88 mdyn Å^?1) than that reported for (CH₃)₃PGaH₃ and the difference possibly reflects the relative stabilities of the donor-acceptor bond in the two complex species.The fact that none of the A, modes appear as doublets in the spectra, nor are any of the E modes split except for the GaC₃ antisymmetric stretch, which is believed to be due to the two isotopes of gallium, indicates that there is only one molecule per primitive cell sitting on a C_3v or C₃ site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

Spectra and structure of silicon-containing compounds. XXX. Raman and infrared spectra,conformational stability,vibrational assignment of chloromethyl silyl dichloride

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

Raman and infrared spectra, conformational stability, barriers to internal rotation, vibrational assignment, and ab initio calculations of 3-methyl-3-butenenitrile

The Raman (3500-30 cm⁻¹) spectra of liquid and solid and the infrared (3500-40 cm⁻¹) spectra of gaseous and solid 3-methyl-3-butenenitrile, CH₂C(CH₃)CH₂CN, have been recorded. Both cis and gauche conformers have been identified in the fluid phases but only the cis form remains in the solid. Variable temperature (−55 to −100 °C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. From these data, the enthalpy difference has been determined to be 163±16 cm⁻¹ (1.20±0.19 kJ mol⁻¹), with the cis conformer the more stable rotamer. It is estimated that there is 48±2% of the gauche conformer present at  25°C. A complete vibrational assignment is proposed for the cis conformer based on infrared band contours, relative intensities, depolarization ratios and group frequencies. Several of the fundamentals for the gauche conformer have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries have been obtained for both rotamers by ab initio calculations employing the 6-31G(d), 6-311G(d,p), 6-311+G(d,p) and 6-311+G(2d,2p) basis sets at the levels of restricted Hartree-Fock (HF) and/or Møller-Plesset perturbation theory to the second order (MP2). Only with the 6-311G(2d,2p) and 6-311G(2df,2pd) basis sets with or without diffuse functions is the cis conformer predicted to be more stable than the gauche form. The potential energy terms for the conformational interchange have been obtained at the MP2(full)/6-311+G(2d,2p) level, and compared to those obtained from the experimental data. The results are discussed and compared to the corresponding quantities obtained for some similar molecules.     

Raman and infrared spectra,conformational stability,barriers to internal rotation,r 0 structural parameters,ab initio calculations,and vibrational assignment for vinyl chloroformate

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. Ther ₀ 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.     

Infrared and Raman spectra, ab initio calculations of structure and vibrational assignment of 1-fluoro-2-butyne.

The infrared spectra (3500-50 cm(-1)) of the gas and solid and the Raman spectra (3500-50 cm(-1)) of the liquid and solid have been recorded for 1-fluoro-2-butyne, CH3-C-triple bond-C-CH2F. Equilibrium geometries and energies have been determined by ab initio and hybrid DFT methods using a number of basis sets. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on vibrational-rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH3 group exhibits almost completely free rotation which is in agreement with the observation of Coriolis sub-band structure in two of the degenerate methyl vibrations. The results are compared to the corresponding quantities for some similar molecules.     

Spectra and structure of silicon containing compounds. XXVII. Raman and infrared spectra, conformational stability, vibrational assignment and ab initio calculations of vinyldichlorosilane

The infrared (3200-30 cm(-1) spectra of gaseous and solid and the Raman spectra of liquid (3200-30 cm(-1), with quantitative depolarization values, and solid vinyldichlorosilane, CH2=CHSiHCl2, have been recorded. Both the gauche and the cis conformers have been identified in the fluid phases. Variable temperature (105-150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy difference has been determined to be 20 +/- 5 cm(-1) (235 +/- 59 J mol(-1) with the gauche conformer the more stable rotamer. It was not possible to obtain a single conformer in the solid even with repeated annealing of the sample. The experimental enthalpy difference is in agreement with the prediction from MP2/6-311 + G(2d,2p) ab initio calculations with full electron correlation. However, when smaller basis sets, i.e. 6-31G(d) and 6-311 + G(d,p) were utilized the cis conformer was predicted to be the more stable form. Complete vibrational assignments are proposed for both conformers based on infrared contours, relative infrared and Raman intensities, depolarization values and group frequencies, which are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. From the frequencies of the Si-H stretches, the Si-H bond distance of 1.474 A has been determined for both the gauche and the cis conformers. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G(d), 6-311 + G(d,p) and 6-311 + (2d,2p) basis sets at level of Hartree-Fock (RHF) and/or Moller Plesset to the second order (MP2) with full electron correlation. The potential energy terms for the conformer interconversion have been obtained from the MP2/6-31G(d) calculations. The results are discussed and compared with those obtained for some similar molecules.     

Spectra and structure of silicon containing compounds. XXXIX. Raman and infrared spectra,conformational stability,vibrational assignment and ab initio calculations of n-propyltrifluorosilane

The infrared (3100-40 cm(-1)) spectra of gaseous and solid and Raman (3200-20 cm(-1)) spectra of liquid with qualitative depolarization values and solid n-propyltrifluorosilane, CH(3)CH(2)CH(2)SiF(3), have been recorded. Additionally the infrared spectra of the sample in nitrogen and argon matrices have been recorded. Both the anti and gauche conformers have been identified in the fluid phases but only the anti conformer remains in the solid. Variable temperature (-105 to -150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been recorded and the enthalpy difference has been determined to be 135+/-14 cm(-1) (1.62+/-0.17 kJ mol(-1)) with the anti conformer the more stable form. At ambient temperature it is estimated that there is 51+/-2% of the gauche conformer present. Also the enthalpy difference in the liquid was obtained from variable temperature studies of the Raman spectra and from three conformer pairs an average value of 179+/-18 cm(-1) (2.14+/-0.22 kJ mol(-1)) was obtained again with the anti form the more stable conformer. Relatively complete vibrational assignments are proposed for both conformers based on the relative infrared and Raman spectral intensities, infrared band contours, depolarization ratios which are supported by normal coordinate calculations. The geometrical parameters, harmonic force constants, vibrational frequencies, infrared intensities, Raman activities, depolarization ratios, and energy differences have been obtained for the anti and gauche conformers from ab initio MP2/6-31G(d) calculations. Structural parameters and energy differences have also been obtained utilizing the larger 6-311+G(d, p) and 6-311+G(2d, 2p) basis sets. By utilizing the previously reported microwave rotational constants for five isotopomers of CH(3)SiF(3) along with ab initio predicted structural values, r(0) parameters have been obtained for methyltrifluorosilane. Similarly, from the ab initio predicted parameters "adjusted r(0)" parameters have been estimated for both conformers of n-propyltrifluorosilane. The results are discussed and compared with those obtained for some similar molecules.     

Conformational analysis,barriers to internal rotation,vibrational assignment and ab initio calculations of chloroacetone

The infrared (3500-20 cm⁻¹) and Raman (3200-10 cm⁻¹) spectra have been recorded for gaseous and solid chloroacetone (1-chloro-2-propanone), CH₂ClC(O)CH₃. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. These data have been interpreted on the basis that the molecule exists predominantly in a gauche conformation having a “near cis” structure of C₁ symmetry (dih ClCCO=142°C) in the vapor but for the liquid a second conformer having a trans structure (chlorine atom oriented trans to the methyl group) with C_s point group symmetry is present. From a study of the Raman spectrum of the liquid at variable temperatures, the trans conformation has been determined to be more stable than the gauche form by 1042±203 cm⁻¹ (2.98±0.6 kcal mol⁻¹ and is the only conformer present in the spectrum of the annealed solid. From ab initio calculations at the 3-21G* and 6-31G* basis set levels optimized geometries for both the gauche and trans conformers have been obtained and the potential surfaces governing internal rotation of the symmetric and asymmetric rotors have been obtained. The observed vibrational frequencies and assignments to the fundamental vibrations for both the gauche and trans conformers are compared to those calculated with the 3-21G* basis set. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.     

Conformational analysis,barriers to internal rotation,ab initio calculations and vibrational assignment of fluoroacetone

The infrared (3500-20 cm⁻¹) and Raman (3200-10 cm⁻¹) spectra have been recorded for gaseous and solid fluoroacetone (1-fluoro-2-propanone), CH₂FC(O)CH₃. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. These data have been interpreted on the basis that the molecule exists predominantly in the cis (fluorine atom oriented cis to the methyl group) conformation in the vapor but for the liquid a second conformer having a trans orientation (fluorine atom oriented trans to the methyl group) is present. From a study of the Raman spectrum of the liquid at variable temperatures the trans conformation has been determined to be more stable than the cis form by 416 ± 54 cm⁻¹ (1.19 ± 0.15 kcal mol⁻¹) and is the only conformation present in the spectrum of the annealed solid. The asymmetric torsional fundamental for the more stable cis conformer has been observed in the far infrared spectrum of the gas at 69.6 cm⁻¹ with six accompanying hot band transitions proceeding to lower frequency. The corresponding mode for the high energy trans conformer is extensively overlapped but is distinguishable at ∼65 cm⁻¹. From these data the asymmetric torsional potential function governing internal rotation about the CC bond has been determined and the potential coefficients are: V₁ = 675 ± 2, V₂ = 991 ± 5, V₃ = 74 ± 1 and V₄ = 54 ± 2 cm⁻¹. The cis to trans and trans to cis barriers are 1332 ± 5 and 731 ± 5 cm⁻¹, respectively, with an enthalpy difference of 601 ± 8 cm⁻¹ (1.72 ± 0.02 kcal mol⁻¹). From ab initio calculations at the 3-21G and 6-31G* basis set levels optimized geometries for both the cis and trans conformers have been obtained and the potential surface governing internal rotation of the asymmetric top determined. The observed vibrational frequencies with their assignments for both the cis and trans conformers are compared to those from the ab initio calculations. All of these results are compared to the corresponding quantities for some similar molecules.     

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of ethynylmethyl cyclobutane.

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