Complete assignment of vibrational spectra of 1,5-cyclooctadiene—a theoretical and experimental infrared and Raman study (original) (raw)
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Vibrational analysis of 1-chlorooctane
Indian Journal of Physics, 2010
The organic compound 1-chlorooctane exists in liquid state at ambient temperatures and has numerous synthetic applications. Fourier transform infrared and Raman spectra of this molecule have been recorded in the range of 4000−400 cm−1 and 3500−200 cm−1, respectively. A detailed vibrational analysis in terms of assignment of the observed frequencies of this molecule for its four most probable conformations in
2000
The Raman (3500-40 cm − 1 ) and infrared (3500-70 cm − 1 ) spectra of gaseous and solid 2-methoxypropene, CH 3 O(CH 3 )C --CH 2 , and the isotopomers, CD 3 O(CH 3 )C --CH 2 and CH 3 O-(CD 3 )C --CD 2 have been recorded. In addition, the Raman spectra of the liquids have been recorded with qualitative depolarization measurements. All of these data indicate that only one conformer is present in the fluid phases at ambient temperature and this form is the cis conformer, which remains in the solid. Assignments are provided for the fundamentals of all three isotopomers for the cis conformer with C s symmetry. The far-infrared spectra of all three isotopic species have been recorded at a resolution of 0.1 cm − 1 in the gas and 1.0 cm − 1 in the solid. The parameters of the potential function governing the asymmetric torsion are determined to be V 3 1485 ± 9 cm − 1 and V 6 − 55 ± 4 cm − 1 for the d 0 compound, where only two terms were determined, since a second conformer was not evident. The barrier to internal rotation for the methyl group attached to the oxygen atom is 1370 ± 8 cm − 1 and the C -CH 3 barrier is 772 ± 5 cm − 1 . Ab initio calculations with full electron correlation have been carried out by the perturbation method to second order to obtain the equilibrium structural parameters, harmonic force constants, fundamental frequencies, infrared intensities, Raman activities, depolarization values, and conformational stability. The predicted values have been compared to the experimental values where appropriate.
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
1999
The infrared (3500-40 cm Ϫ1) spectra of gaseous and solid 1-methylsilacyclobutane, cC 3 H 6 SiH(CH 3), have been recorded. In addition, the Raman spectrum (3500-30 cm Ϫ1) of the liquid has also been recorded and quantitative depolarization values obtained. Both the axial and equatorial conformers, with respect to methyl group, have been identified in the fluid phases. Variable temperature studies (Ϫ55 to Ϫ100ЊC) 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 122^26 cm Ϫ1 (1.46^0.32 kJ/mol), with the equatorial conformer being the more stable structure. However, with repeated annealing of the amorphous solid, it was not possible to obtain a polycrystalline solid with a single conformer. A complete vibrational assignment is proposed for the equatorial conformer based on infrared band contours, relative intensities, depolarization values and group frequencies. Most of the fundamentals for the axial conformer have also been identified. Utilizing the frequency of the silicon-hydrogen (Si-H) stretching mode, the Si-H distance has been determined to be 1.490 Å for both conformers. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations, employing the 3-21G* and 6-31G* basis sets at the levels of restricted Hartree-Fock (RHF) and/or Moller-Plesset (MP) to second order. The results are discussed and compared with those obtained for some similar molecules.
Spectrochimica acta, 1983
As a first step toward the understanding of the role the zero-point energy of the fast vibrations plays in the effective puckering potential of oxetane, we have evaluated the force field of this molecule at three different values of the puckering angle by ab initio SCF calculations, using the 4-21 basis set. The force constants of the planar configuration, scaled by six empirical parameters, were used to establish the assignment of the high-frequency fundamental vibrations of oxetane and four of its deutero derivatives. Our results support most of the empirical assignments made by KYDD, WIESER and KIEFER, but in each isotopomer one of the B, (out-of-plane) fundamentals must beassigned to a much higher frequency than they assumed. Except for a few cases where deviations up to 40 cm-' occur, as a probable consequence of the inadequate description of ring strain and large anharmonicity connected with puckering, the theoretical spectrum reproduces most experimental frequencies to within 20 cm-'
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012
Infrared and Raman spectra of O,O-dimethyl S-methylcarbamoylmethylphosphorodithioate, dimethoate, have been recorded. Density functional theory, DFT, with the B3LYP functional was used for the optimization of the ground state geometry and simulation of the infrared and Raman spectra of this molecule. Calculated geometrical parameters fit very well with the experimental ones. Based on the recorded data, the DFT results and a normal coordinate analysis based on a scaled quantum mechanical (SQM) force field approach, a complete vibrational assignment was made for the first time.
Chemical Physics, 1988
The inclusion of the anharmonicity of molecular vibrations is an important aspect of the goal of making highly accurate theoretical predictions of the spectroscopic properties of molecules. Recently developed analytic third derivative methods for selfconsistent-field (SCF) wavefunctions have made it possible to determine the complete cubic and quartic force fields of polyatomic molecules, thus allowing the treatment of anharmonic eIfects. Here we continue our systematic evaluation of the performance of such theoretical methods by studying several linear molecules which are well characterized experimentally, viz, HCN, DCN, COs, NsO, QCS, CsH,, and C2Dr. A number of anharmonic molecular properties have been determined, including vibration-rotation interaction constants, vibrational anharmonic constants, fundamental vibrational frequencies, sextic centrifugal distortion constants, rotational constants which include zero-point vibrational corrections, and vibrational and rotational &type doubling constants. These anharmonic molecular constants are not as well converged with respect to basis set enlargement as those which were previously determined for asymmetric top molecules, appanmtly because all the molecules considered here contain multiple bonds. However, the reported anharmonic constants at the SCF level of theory are still in reasonably good agreement with the corresponding experimental constants. Siicant improvements in accuracy are achieved by incorporating electron correlation at the configuration interaction singles and doubles (CISD) level of theory. Standard spectroscopic perturbation theory methods are used in this study, which are directly and immediitely applicable to larger molecular systems than those studied here.