Vibrational spectrum, ab initio calculations, assignments of fundamentals, barriers to internal rotation and stabilities of conformers of 1,2-dichloropropane (original) (raw)
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Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2004
Ab initio calculations are reported for three of four possible conformers of 1,3-dichloropropane. The fourth conformer, with C s symmetry, has a predicted enthalpy difference of more than 1500 cm −1 from the most stable conformer from each calculation regardless of the basis set used, so there is little chance of observing it. Thus, there is no evidence in the infrared or Raman spectrum of the presence of a fourth conformer. The order of stability given by the ab initio calculations is C 2 (GG) > C 1 (AG) > C 2v (AA) > C s (GG ), where A indicates the anti form for one of the CH 2 Cl groups and G indicates the gauche conformation for the other CH 2 Cl group relative to the plane of the carbon atoms. Almost every band observed can be confidently assigned to one or another of the conformers. Many observed bands proved to be of a composite nature, with several nearly coincident vibrations of different conformers contributing to the band contour. Nonetheless, a complete assignment of fundamentals is possible for the most stable C 2 conformer, and 5 of the fundamentals of the C 2v conformer and 13 those of the C 1 conformer can be confidently assigned.
Journal of Molecular Structure, 1997
The infrared (3400-50 cm 21 ) and/or Raman (3400 -10 cm 21 ) spectra of gaseous, xenon solution, liquid and solid 5chloropent-2-yne, CH 2 ClCH 2 CCCH 3 , have been recorded. These data indicate that the molecule exists in the anti (the C -Cl bond is trans to the CxC bond) and the gauche conformations in the vapor and liquid but only the anti conformer remains in the solid state. From a variable temperature infrared study of the xenon solution, the anti conformation has been determined to be more stable than the gauche form by 233^23 cm 21 (2.79^0.28 kJ/mol) and it is estimated that 39% of the sample is in the gauche form at ambient temperature. The optimized geometries, conformation stabilities, harmonic force fields, Raman activities, depolarization ratios, and infrared intensities have been obtained from ab initio MP2/6-31G(d) calculations with full electron correlation. These predicted quantities are compared to the corresponding experimental quantities when appropriate. Equilibrium geometries and energies for both conformers have been obtained from ab initio MP2/6-311G(d,p), MP2/6-311G(2d,2p) and MP2/6-311G(2df,2pd) calculations. Vibrational assignments for the 24 normal modes for the anti conformer are proposed and several of the fundamentals for the gauche conformer are assigned. The sub-band structure on the pseudodegenerate vibrations of the methyl group indicates that it is almost free internal rotation. From this fine structure, the Coriolis coupling constants, j, have been determined. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules. q
The present paper reports main results of a comprehensive study of the structure and vibrational spectra of the stable conformers of chlorocarbonyl ketene computed using second-order perturbation theory treatment based on quadratic, cubic and semidiagonal quartic force constants. It is found that the s-trans conformer is more stable than the s-cis conformer by ∼0.69 kcal/mol. The vibrationally averaged bond lengths and bond angles, both for the cis and trans conformers, are within 0.005 Å and 0.14°, respectively, of the equilibrium geometry. The ab initio and DFT based anharmonic vibrational analysis using second-order perturbation theory provides reliable frequencies (r.m.s. deviation ±20 cm -1 ) and assignments to the vibrational bands. DFT calculations using the same method and basis function for the harmonic frequencies and anharmonic corrections give frequencies in better agreement with the experimental values than those in which the harmonic frequencies from a high level quantum mechanical method (B97-1/aug-cc-pVTZ) are coupled with anharmonic corrections from a cheap model (B3LYP/6-31+G**); the r.m.s. deviation in the latter case is ±47 cm -1 . The errors in the calculation of the fundamental modes are reflected in the overtones and combination bands. Some spectroscopic constants namely, the anharmonic constants, rotational constants and rotation-vibration coupling constants of the two conformers have been calculated by density functional theory and compared with literature, where available.
Journal of Raman Spectroscopy, 2000
The Raman (3500-30 cm K1) spectra of liquid and solid and the infrared (3500-40 cm K1) spectra of gaseous and solid 3-methyl-3-butenenitrile, CH 2 aC(CH 3)CH 2 CbN, 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 (K55 to K100 8C) 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 163G16 cm K1 (1.20G0.19 kJ mol K1), with the cis conformer the more stable rotamer. It is estimated that there is 48G2% of the gauche conformer present at 258C. 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), 6-311CG(d,p) and 6-311CG(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)/6-311CG(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.
Journal of Molecular Structure, 2001
Infrared spectra of n-propyltrichlorosilane (CH 3 CH 2 CH 2 SiCl 3 ) were obtained in the vapour, amorphous and crystalline solid phases in the range 4000-50 cm −1 . Additional spectra in argon and nitrogen matrices at 5 K were recorded before and after annealing to 20-36 K. Raman spectra of the compound as a liquid were recorded at various temperatures between 300 and 153 K and spectra of the amorphous and crystalline solids were obtained. The spectra revealed the existence of two conformers (anti and gauche) in the fluid phases and in the matrices. When the vapour was shock-frozen on a cold-finger at 78 K and subsequently annealed to 120-130 K, 10 Raman bands and eight IR bands of the liquid were reduced in intensity in the amorphous phase and vanished in the crystal. Frequent intensity variations were observed in the infrared spectra of argon and nitrogen matrices before and after annealing. These spectra revealed the existence of one conformer (anti) in the crystal. From intensity variations of four independent pairs of anti and gauche bands in the Raman spectra between 300 and 150 K, an average value 1H • (gauche-anti) = 4.6 ± 0.3 kJ mol −1 was obtained in the liquid. Annealing experiments on n-propyltrichlorosilane in the matrices demonstrate that the gauche bands vanish after annealing, revealing that the anti conformer has the lower energy. The spectra of both conformers were interpreted in detail. Ab initio and DFT calculations gave optimized geometries, infrared and Raman intensities and scaled vibrational wavenumbers for the anti and gauche conformers. The conformational energy difference derived was 7.6 and 6.4 kJ mol −1 for the HF/6-311G * and B3LYP/6-311G * basis sets, respectively, with anti being the low-energy conformer.
Journal of Molecular Structure, 2002
The infrared (3400-50 cm 21 ) and/or Raman (3400 -10 cm 21 ) spectra of gaseous, xenon solution, liquid and solid 5chloropent-2-yne, CH 2 ClCH 2 CCCH 3 , have been recorded. These data indicate that the molecule exists in the anti (the C -Cl bond is trans to the CxC bond) and the gauche conformations in the vapor and liquid but only the anti conformer remains in the solid state. From a variable temperature infrared study of the xenon solution, the anti conformation has been determined to be more stable than the gauche form by 233^23 cm 21 (2.79^0.28 kJ/mol) and it is estimated that 39% of the sample is in the gauche form at ambient temperature. The optimized geometries, conformation stabilities, harmonic force fields, Raman activities, depolarization ratios, and infrared intensities have been obtained from ab initio MP2/6-31G(d) calculations with full electron correlation. These predicted quantities are compared to the corresponding experimental quantities when appropriate. Equilibrium geometries and energies for both conformers have been obtained from ab initio MP2/6-311G(d,p), MP2/6-311G(2d,2p) and MP2/6-311G(2df,2pd) calculations. Vibrational assignments for the 24 normal modes for the anti conformer are proposed and several of the fundamentals for the gauche conformer are assigned. The sub-band structure on the pseudodegenerate vibrations of the methyl group indicates that it is almost free internal rotation. From this fine structure, the Coriolis coupling constants, j, have been determined. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules. q
Journal of Molecular Structure, 2012
The infrared spectra of 3-butyn-1-ol, HC"CCH 2 CH 2 OH, have been recorded as a vapour in the range 3600-50 cm À1 and as a liquid between 3600 and 400 cm À1. Additional spectra of the alcohol isolated in an argon matrix at ca. 5 K were obtained and spectra were recorded after annealing to various temperatures between 10 and 35 K. Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 143 K. Spectra of an amorphous solid were recorded at 78 K. 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 AC"CA bond, or a third conformer ag, the conformational enthalpy difference was found to be D conf H(ag-gg) = 0.9 kJ mol À1 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 4.2 kJ mol À1 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.
Journal of Molecular Structure, 2001
The infrared spectra of 1,2-diphenylethane were recorded as a melt and crystalline solid in capillary films and as a pellet in KBr and polyethylene in the 4000-50 cm 21 range. Moreover, the sample was isolated in an argon matrix at ca. 5 K, and the spectra recorded in the range 3100-450 cm 21 , before and after annealing. Raman spectra of the melt were recorded between 295 (supercooled) and 357 K, and spectra of the crystalline solid were obtained at ambient temperature.
Vibrational spectra, conformational equilibrium and ab initio calculations of 1,2-diphenylethane
Journal of Molecular Structure, 2004
The infrared spectra of 1,2-diphenylethane were recorded as a melt and crystalline solid in capillary films and as a pellet in KBr and polyethylene in the 4000-50 cm 21 range. Moreover, the sample was isolated in an argon matrix at ca. 5 K, and the spectra recorded in the range 3100-450 cm 21 , before and after annealing. Raman spectra of the melt were recorded between 295 (supercooled) and 357 K, and spectra of the crystalline solid were obtained at ambient temperature.