Raman spectra of 1,1-dicyclopropyl-2,2-dimethylethene (c-C3H5)(2)C = C(CH3)(2)) as a liquid were obtained at 293 K and polarization data recorded. Additional Raman spectra were observed at various temperatures between 293 and 143 K, and intensity changes of certain bands with temperature detected. When the sample was cooled to 153 K an amorphous solid appeared; upon slow warming it turned crystalline at 188 K and melted at higher temperatures. Various predominantly weak bands observed in the liquid and amorphous solid vanished in the Raman spectrum of the crystalline phase indicating the occurrence of two or more conformers in the liquid and amorphous phases. Van't Hoff plots of selected band pairs revealed an enthalpy difference of 2.0 +/- 0.2 kJ mol(-1) between the two most abundant conformers in the liquid. The vapour infrared spectrum was studied in the 4000-400 cm(-1 )region. Quantum chemical calculations were carried out to identify possible stable conformers and their vibrational wavenumbers, IR and Raman intensities and depolarization properties. A potential energy surface scan, obtained by rotating the geminal cyclopropyl-groups independently, disclosed occurrence of two dominant conformers of symmetries C-2 and C-1 with an enthalpy difference of around 4 kJ mol(-1) and separated by a low barrier of ca. 6 kJ mol(-1), indicating a flexible molecule where the cyclopropyl groups may rotate partially. Three additional local minima on the PES were found with relative enthalpies above 15 kJ mol(-1), suggesting near absence of these conformers at ambient temperature and pressure. (C) 2019 Elsevier B.V. All rights reserved.

The infrared and Raman spectra of 1,1,3,3,5,5-hexafluoro-1,3,5-trisilacyclohexane (c-C3H6Si3F6) as a solid powder have been recorded. The vibrational spectra reveal that the crystalline compound exists as a chair conformer with C3v symmetry at ambient temperature. Additional conformers such as twist or boat were not detected although quantum chemical calculations indicated a negligible energy difference between chair, twist and boat forms. The wavenumbers of the IR and Raman bands were measured and the assignments were initially supported by quantum chemical B3LYP/cc-pVTZ calculations in the harmonic approximation. These vibrational modes were scaled with a common factor of 0.98, and the 11 totally symmetric A1 and 16 doubly degenerate E fundamentals were assigned on the basis of the infrared and Raman intensities. An average relative deviation of ca. 2.9% between the observed and the scaled harmonic calculations was found. Additional calculations were made in the anharmonic approximation, in which the symmetry was reduced to Cs symmetry by a slight distortion of the hexagonal ring. Employing these calculations without scaling, a better agreement between the observed and calculated wavenumbers was obtained (1.5%). Further calculations, involving a twist conformer was not consistent with the spectral results, neither in terms of the number of modes nor their wavenumbers.

The infrared spectra of 1,3,5-trisilacyclohexane (c-C3H6Si3H6) as a vapour and liquid have been recorded. Raman spectra of the liquid have been studied and depolarization data were obtained. The compound exists in the stable form as a chair conformer with C3v symmetry, and additional conformers such as twist or cradle forms were not detected. The wavenumbers of the IR and Raman active vibrational modes were measured and their existence were supported by quantum chemical B3LYP/cc-pVTZ calculations in the harmonic approximation. The 11 totally symmetric A1 and 16 doubly degenerate E fundamentals were assigned on the basis of the infrared vapour contours and intensities and upon the Raman intensities and depolarization measurements. Quantum chemistry calculations support the assignments: an average relative deviation between observed and calculated wavenumbers of 2.2% was obtained employing scaling of the harmonic B3LYP/cc-pVTZ force field, which was reduced to 1.4% in the anharmonic calculations.

A 1,1-disubstituted silacyclohexane, 1-chloro-1-methyl-1-silacyclohexane, C5H10SiClCH3, was synthesized and studied by infrared and Raman spectroscopy. The infrared spectra of the vapor and liquid were recorded at ambient temperature and the solid sample investigated at 78 K. Negligible spectral changes ocurred at 78 K compared with the fluid state, but after annealing to ca. 165 K an apparent crystal was formed. Raman spectra of the liquid were recorded at 293 K and depolarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K. A supercooled liquid appeared after slow cooling, but an amorphous solid phase was observed after shock freezing to 78 K. After annealing, a plastic phase was observed and an anisotropic crystal appeared after further annealing. In the crystalline phase spectral shifts and some vanishing bands were observed and only the a (Cl) conformer remained. The compound exists in two conformers, equatorial (Cl) (e) and axial (Cl)(a) in the liquid, amorphous and plastic phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 1.5 ± 0.5 kJ mol−1 lower enthalpy than e in the liquid. B3LYP calculations with various basis sets and the G3 model chemistry gave conformational energy difference ΔE (a–e) in the range 3.2–2.4 kJ mol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the two conformers were calculated. The 32 A′ and 25 A″ modes for the e(Cl) and a(Cl) conformations were assigned, supported by anharmonic B3LYP/cc-pVTZ calculations.

Raman spectra of 1,1-difluoro-1-silacyclohexane as a liquid, and as a solid at 78 K were recorded and depolarization data obtained. The infrared spectra of the vapour, liquid and amorphous and crystalline solids have been studied. In the low temperature IR and Raman spectra eight and three bands, respectively, were shifted a few cm(-1) when the sample crystallized. No bands vanished after crystallization in agreement with the assumption that only one conformer (chair) was present in all the states of aggregation. The compound exists in the stable chair conformation, whereas in the parent silacyclohexane a possible twist form should have more than 15 kJ mol(-1) higher energies than the chair, as derived from various calculations. The wavenumbers of the vibrational modes were calculated in the harmonic and anharmonic approximation employing B3LYP/cc-pVTZ calculations. The 27 A' and 21 A″ fundamentals were assigned on the basis of the calculations, infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of 1.5% was found between the observed and the anharmonic wavenumbers for the 48 modes.

Raman spectra of of 1-methyl-1-silacyclohexane as a liquid were recorded at 293K and depolarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143K, and intensity changes with temperature of certain Raman bands were detected. A supercooled liquid appeared after slow cooling, but an amorphous phase was observed after shock freezing to 78K. After annealing, first a plastic phase and subsequently a crystal were observed. In the crystalline phase spectral shifts and some vanishing bands were observed.The infrared spectra of the vapor and liquid were studied at ambient temperature and the solid sample investigated at 78K. Negligible spectral changes ocurred at 78K compared with the fluid state, but after annealing to ca. 170K an apparent crystal was formed and a few bands vanished and others were shifted.The compound exists in two conformers, equatorial (e) and axial (a) in the liquid, amorphous and plastic phases, but only the e-conformer was present in the crystal. The experimental results suggest that the e-conformer has 0.6kJmol−1 lower energy than a in the liquid.B3LYP calculations with various basis sets gave a conformational enthalpy difference ΔH (a–e) around 2.4kJmol−1 while G3 model chemistry gave 0.6kJmol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The fundamental wavenumbers were also derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations. A relative deviation of 0.94% and 1.31% between the observed and calculated wave numbers for the 57 modes of the e-and a-conformers, respectively, was obtained.

The infrared spectra of 1-chloro-1-silacyclohexane have been studied as a vapour and liquid at ambient temperature and as amorphous and annealed crystalline solids at 78K. Various infrared bands present in the vapour and liquid states vanished in the crystalline state upon cooling. Raman spectra of the liquid were recorded at 293 K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163 K, and intensity changes with temperature of certain Raman bands were detected. A crystalline phase was observed around 140 K, leading to spectral shifts and a number of vanishing bands.The compound exists in two conformers, equatorial (e) and axial (a) in the fluid phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 2.8 kJ mol(-1) lower enthalpy than e in the liquid, leading to 69% of the a conformer at 293 K.B3LYP calculations with various basis sets and the G3 model chemistry gave conformational energy difference Delta E(e - a) in the range 0.4-1.4 kJ mol(-1). Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The fundamental wavenumbers were also derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations, a relative deviation of less than 2% between the observed and calculated wave numbers for the 48 modes of the e- and a-conformers was obtained. (C) 2012 Elsevier B.V. All rights reserved.

Raman spectra of 1-fluoro-1-silacyclohexane as a liquid were recorded at 293K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143K, and intensity changes of certain bands with temperature were investigated. An apparently plastic phase was observed around 170K, but no definite crystallization was ever obtained on cooling. The infrared spectra have been studied of the vapor, of an amorphous solid at 78K and of the liquid in the range 600–100cm−1. No infrared bands present in the vapor or liquid vanished upon cooling.The compound exists a priori in two conformers, equatorial (e) and axial (a), and the experimental results suggest an equilibrium in which the a-conformer has 1.2kJmol−1 lower enthalpy than the e-conformer in the liquid, leading to 60% a-conformer at ambient temperature.B3LYP calculations with various basis sets and the G3 model chemistry gave conformational enthalpy difference ΔH(e−a) in the range 0.6 and 1.8kJmol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The wavenumbers of the vibrational modes were derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations. An average relative deviation of ca. 1% between the observed and calculated wavenumbers for the 48 modes of the e and a conformers was found.

Raman spectra of silacyclohexane as a liquid was recorded and depolarization data obtained. The infrared spectra of the vapour and liquid have been studied.The compound exists in the stable chair conformation, whereas a possible twist form should have more than 15kJmol−1 higher energies for silacyclohexane derived from numerous calculations. The wavenumbers of the vibrational modes were derived in the harmonic and anharmonic approximation in B3LYP/cc-pVTZ calculations. The 27 A′ and 21 A″ fundamentals were assigned on the basis of the calculations, on infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of ca 0.77% was found between the observed and the anharmonic wavenumbers for the 48 modes.

The infrared spectra of 1-pentyne (CH3CH2CH2CCH) have been studied as a vapour and as a crystalline solid at 78K. Raman spectra of the liquid were recorded at 293K and polarization data were obtained. Additional Raman spectra of the liquid were recorded at various temperatures between 295 and 183K. Several Raman bands vanished in the low temperature solid at 160K, and both the IR and Raman spectra revealed that only one conformer was present in the crystal lattice.

Raman spectra of cyclopropylmethyl dichlorosilane (c-C3H5)SiCl2CH3 as a liquid were recorded at 293 K and polarization data were obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163K, and intensity changes of certain bands with temperature were detected. No crystallization was ever obtained in the Raman cryostat in spite of extensive annealing. The infrared spectra have been studied as a vapour, as an amorphous solid at 78K and as a liquid in the range 600-100 cm(-1). No infrared bands present in the vapour or liquid seemed to vanish upon cooling, and the sample never formed crystals on the Csl window of an infrared cryostat.The compound exists a priori in two conformers, syn and gauche, and the experimental results suggest an equilibrium in which the gauche conformer has 1.64 kJ mol(-1) lower enthalpy than syn in the liquid, leading to 20%syn at ambient temperature. Most of the syn bands were situated close to the corresponding gauche bands and it was difficult to obtain reliable AN values.B3LYP calculations with various basis sets and the CBS-QB3 and G2 and G3 models were employed, yielding the conformational enthalpy difference Delta H(syn-gauche) between 2.6 and 3.4 kJ mol(-1). Infrared and Raman intensities, polarization ratios and vibrational frequencies for the syn and gauche conformers were calculated. Instead of scaling the calculated wavenumbers in the harmonic approximation, calculations from B3LYP/cc-pVTZ were derived in the anharmonic approximation. In most cases these values were in good agreement with the experimental results for 38 observed modes of the gauche and 8 modes of the syn conformer with a deviation of ca. 1%. (C) 2011 Elsevier B.V. All rights reserved.

The infrared spectra of ethylmethylgermane (CH(3)CH(2)GeH(2)CH(3)) have been studied as a vapour in the 4000-400 and 500-100 cm(-1) regions and as an amorphous solid at 78 K. Raman spectra of the sample as a liquid were recorded at 293 K and polarization data were obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143 K, and small intensity changes of certain bands with temperature were detected. The sample was also investigated as an amorphous solid on a cold finger of copper or a Cslwindow at 78 K. No crystallization was ever obtained in the Raman or infrared cryostats in spite of extensive annealing.The compound exists a priori in two conformers, anti and gauche, and the variable temperature Raman spectra suggest an equilibrium in which the gauche conformer has 0.4 kJ mol(-1) lower enthalpy than anti in the liquid.B3LYP and MP2 calculations with various basis sets and the CBS-QB3 and G2 models were employed, yielding an average conformational enthalpy difference Delta H(anti-gauche) = 0.24 kJ mol(-1). Infrared and Raman intensities, polarization ratios and vibrational frequencies for the gauche and anti conformers were calculated. Instead of scaling the calculated wavenumbers in the harmonic approximation, performed in our previous publications, calculations from B3LYP/cc-pVTZ were derived in the anharmonic approximation. In most cases these values gave a good agreement with the experimental results for 34 observed modes of the gauche and 10 modes of the anti conformer. (C) 2010 Elsevier B.V. All rights reserved.

Raman spectra of ethylmethyldichlorogermane (CH3CH2GeCl2CH3) as a liquid were recorded at 293 K and polarization data were obtained. Additional Raman spectra were recorded at various temperatures between 293 and 154 K, and intensity changes of certain bands with temperature were detected. The sample was also investigated as amorphous and crystalline solids on a cold finger of copper at 78 K. The infrared spectra have been studied as a vapour in the 4000–400 and 500–100 cm−1 regions and as amorphous and crystalline solids at 78 K. No Raman or infrared bands present in the liquid seemed to vanish completely upon crystallization, but considerable intensity changes were observed, indicating a partly crystallization. The compound exists a priori in two conformers, anti and gauche, and the experimental results suggest an equilibrium in which the anti conformer has 0.6 kJ mol−1 lower enthalpy than gauche in the liquid. In the partly crystalline solid, however, the results indicate gauche to be preferred in the crystal lattice. DFT/B3LYP, CBS-QB3 and G2 calculations were carried out indicating a conformational enthalpy difference ΔH(gauche–anti) between 0.8 and 1.5 kJ mol−1, somewhat higher than the experimental value. Vibrational frequencies, infrared and Raman intensities, and polarization ratios for the anti and gauche conformers were calculated. Anharmonic vibrational wavenumbers were derived in B3LYP/cc-pVTZ. In most cases these values gave a good agreement with the experimental results for the anti and gauche conformers.

The infrared spectra (3100–40cm−1) of gaseous and amorphous solid and Raman spectra (3200–20cm−1) of the liquid at various temperatures for methylgermylcyclopropane, c-C3H5GeH2CH3, have been obtained. Additionally, variable temperature (−55 to −100°C) studies of the infrared spectra of the sample dissolved in xenon have been recorded. From these spectral data, two conformers have been identified with one the cis (syn) form where the methyl group is over the three-membered ring and the other the gauche form. By utilizing six conformer pairs of the vibrational bands the enthalpy difference of the sample dissolved in xenon has been determined to be 43±11cm−1 (0.51±0.13kJmol−1) with the gauche form the more stable conformer. It is estimated that there is approximately 30±3% of the cis form present at ambient temperature. It was not possible to achieve crystallization of the compound by annealing it, and both conformers were present at all temperatures. The Ge–H distances of 1.531 and 1.533Å for the gauche conformer have been determined from their stretching frequencies. By utilizing the microwave rotational constants of the gauche conformer for five isotopomers (70Ge, 72Ge, 73Ge, 74Ge, 76Ge) combined with the structural parameters predicted from the MP2(full)/6-311+G(d,p) calculations, the adjusted r0 structural parameters have been obtained. The heavy atom distances (Å) are: (GeC2)=1.925(5); (C2C4)=1.517(3); (C2C5)=1.519(3); (C4C5)=1.502(3); (GeC6)=1.947(5) and the angles (°) are: ∠CGeC=110.6(5); ∠GeC2C4=120.1(5); ∠GeC2C5=119.2(5). For the cis form very small differences of 0.003 and 0.001Å from those of the gauche form are predicted for the GeC bonds whereas the other distances are predicted to be the same or differ at the most by 0.002Å. A complete vibrational assignment is given for both the conformers. To support the vibrational assignments, normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values and infrared band contours. Barriers to internal rotation have been predicted. The results are discussed and compared to the corresponding properties of some similar molecules.

Infrared spectra of 1,2-bis(trifluorosilyl)ethane (SiF3CH2CH2SiF3) were obtained in the vapour and liquid phases, in argon matrices and in the solid phase. Raman spectra of the compound as a liquid were recorded at various temperatures between 293 and 270 K and spectra of an apparently crystalline solid were observed. The spectra revealed the existence of two conformers (anti and gauche) in the vapour, liquid and in the matrix. When the vapour was chock-frozen on a cold finger at 78 K and annealed to 150 K, certain weak Raman bands vanished in the crystal. The vibrational spectra of the crystal demonstrated mutual exclusion between IR and Raman bands in accordance with C-2h symmetry. Intensity variations between 293 and 270 K of pairs of various Raman bands gave Delta H(gauche - anti) = 5.6 +/- 0.5 kJ mol(-1) in the liquid, suggesting 85% anti and 15% gauche in equilibrium at room temperature. Annealing experiments indicate that the anti conformer also has a lower energy in the argon matrices, is the low-energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted, and 34 anti and 17 gauche bands were tentatively identified. Ab initio and density functional theory (DFT) calculations were performed giving optimized geometries, infrared and Raman intensities and anharmonic vibrational frequencies for both conformers. The conformational energy difference derived in CBS-QB3 and in G3 calculations was 5 kJ mol(-1). Copyright (C) 2009 John Wiley & Sons, Ltd.

The infrared spectra of 3-pentyn-2-ol, CH3CCCH(OH)CH3, have been recorded as a vapour and liquid at ambient temperature, as a solid at 78K in the 4000–50cm−1 range and isolated in an argon matrix at ca. 5K. Infrared spectra of the solid phase at 78K were obtained before and after annealing to temperatures of 120 and 130K. The IR spectra of the solid were quite similar to that of the liquid.

The title compounds trans- and cis-2,2,2',2'-tetrachloro-3,3,3',3'-tetramethyl-bicyclopopylidene were synthesized, and their infrared and Raman spectra were recorded. Non-coincidence between the IR and Raman bands of the trans compound suggested C(2h) symmetry and a planar ring system. In the cis compound most of the IR and Raman bands coincided and a C(2v) symmetry seems likely. The exocyclic CC double bond gave rise to a medium/weak Raman band at 1,847 cm(-1) in the trans compound. In the cis derivative IR and Raman bands both at 1,825 cm(-1) were observed. From similarities with related molecules, the ring breathing, the antisymmetric ring stretch, the CCl(2) out-of-phase and in-phase stretch and the out-of-plane ring bending modes have been tentatively assigned for the trans and cis compounds.

Raman spectra of 1,3-disilabutane (SiH3CH2SiH2CH3) as a liquid were recorded at 293 K and as a solid at 78 K. In the Raman cryostat at 78 K an amorphous phase was first formed, giving a spectrum similar to that of the liquid. After annealing to 120 K, the sample crystallized and large changes occurred in the spectra since more than 20 bands present in the amorphous solid phase vanished. These spectral changes made it possible to assign Raman bands to the anti or gauche conformers with confidence. Additional Raman spectra were recorded of the liquid at 14 temperatures between 293 and 137 K. Some Raman bands changed their peak heights with temperature but were countered by changes in linewidths, and from three band pairs assigned to the anti and gauche conformers, the conformational enthalpy difference Delta H-conf(gauche-anti) was found to be 0 +/- 0.3 kJ mol(-1) in the liquid. Infrared spectra were obtained in the vapor and in the liquid phases at ambient temperature and in the solid phases at 78 K in the range 4000-400 cm(-1). The sample crystallized immediately when deposited on the CsI window at 78 K, and many bands present in the vapor and liquid disappeared. Additional infrared spectra in argon matrixes at 5 K were recorded before and after annealing to temperatures 20-34 K. Quantum chemical calculations were carried out at the HF, MP2 and B3LYP levels with a variety of basis sets. The HF and DFT calculations suggested the anti conformer as the more stable one by ca 1 kJ mol(-1), while the MP2 results favored gauche by up to 0.4 kJ mol(-1). The Complete Basis Set method CBS-QB3 gave an energy difference of 0.1 kJ mol(-1), with anti as the more stable one. Scaled force fields from B3LYP/cc-pVQZ calculations gave vibrational wavenumbers and band intensities for the two conformers. Copyright (C) 2007 John Wiley & Sons, Ltd.

The infrared spectra of 3-butyn-1-ol, HCCCH2CH2OH, have been recorded as a vapour in the range 3600–50cm−1 and as a liquid between 3600 and 400cm−1. Additional spectra of the alcohol isolated in an argon matrix at ca. 5K were obtained and spectra were recorded after annealing to various temperatures between 10 and 35K.Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 143K. Spectra of an amorphous solid were recorded at 78K. In spite of several attempts and many different annealing temperatures, the sample crystallized neither in the IR nor in the Raman cryostats. In the variable temperature Raman spectra, some bands of the liquid changed in relative intensity and were interpreted in terms of conformational equilibria between two of the five possible conformers. Complete assignments were made for all the bands of the most stable conformer gg, in which the OH group is approaching the triple bond, forming an intramolecular hydrogen bond. From various bands assigned to a second conformer aa, in which OH is oriented anti to the CC bond, or a third conformer ag, the conformational enthalpy difference was found to be ΔconfH(ag-gg)=0.9kJmol−1 in the liquid. The two highest energy conformers g’g and ag were not detected.Quantum-chemical calculations have been carried out at the MP2 and B3LYP levels with a variety of basis sets. The calculations revealed that gg was the low energy conformer and CBS-QB3 calculations suggested the gg conformer was more stable by 5.4 and 4.2kJmol−1 relative to ag and aa, respectively, in the vapour. Vibrational wavenumbers and infrared and Raman band intensities for the three low energy conformers are reported from B3LYP/cc-pVTZ calculations.

Raman spectra of 1,3-disilabutane (SiH3CH2SiH2CH3) were recorded as a liquid at room temperature and at 14 temperatures between 293 and 137 K. Spectra of an amorphous and annealed solid were recorded at 78 K, and very distinct changes occurred on crystallization. In the variable temperature Raman spectra, some bands changed in intensity and were interpreted in terms of conformational equilibria between the two possible conformers. Complete assignments were made for all the bands of the most stable conformer, anti. From three band pairs assigned to the anti and gauche conformers, the conformational enthalpy differences Delta H(gauche-anti) were found to be between 1.3 kJ mol(-1) and 1.7 kJ mol(-1), using peak heights, and the more stable anti conformer was present in the crystal. A lower value of 0 +/- 0.3 kJ mol(-1) was obtained employing band areas. Ab initio calculations in the RHF and MP2 approximations and DFT calculations were carried out pointing to the anti conformer as the low energy form.