Doddamani S B, Ramoji Anuradha, Yenagi Jayashree, Tonannavar J
Department of Physics, Karnataka University, Dharwad 580 003, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2007 May;67(1):150-9. doi: 10.1016/j.saa.2006.06.038. Epub 2006 Jul 4.
The Raman (3500-50 cm(-1)) and infrared (4000-200 cm(-1)) spectra of 3-chloro, 4-chloro and 5-chloro-2-methylphenyl isocyanates have been measured. Ab initio and density functional theory calculations, at the levels of RHF/6-311G* and B3LYP/6-311G*, have been performed: energies, optimized geometrical parameters, vibrational frequencies, infrared intensities, Raman activities, depolarization ratios and nuclear displacements are obtained. Potential energy distributions (PEDs) and normal modes, for the spectral data computed at B3LYP/6-311G*, have also been obtained from a force-field calculations. A complete vibrational assignments of the observed spectra have been proposed. The force-field calculations have shown that, several of the normal modes are coupled, as is the case with large molecular systems possessing very low or no symmetry, such as investigated in the present study. Further, the investigation of the internal rotation of the isocyanate, NCO, by B3LYP/6-31G* level of theory has shown that the moiety maintains nearly the same orientation in all the three compounds (approximately 140-145 degrees tilt to the para-position) as in phenyl isocyanate. Two conformers, cis and trans forms, with respect to the substituents, NCO and CH(3), have been determined: the cis form lies above trans form by less than a kilocalorie per mole for each compound.
已测量了3-氯、4-氯和5-氯-2-甲基苯基异氰酸酯的拉曼光谱（3500 - 50 cm⁻¹）和红外光谱（4000 - 200 cm⁻¹）。在RHF/6 - 311G和B3LYP/6 - 311G水平上进行了从头算和密度泛函理论计算：获得了能量、优化的几何参数、振动频率、红外强度、拉曼活性、去极化率和核位移。还通过力场计算获得了在B3LYP/6 - 311G水平上计算的光谱数据的势能分布（PEDs）和简正模式。已对观察到的光谱提出了完整的振动归属。力场计算表明，正如本研究中所研究的具有非常低对称性或无对称性的大分子系统那样，几个简正模式是耦合的。此外，通过B3LYP/6 - 31G理论水平对异氰酸酯NCO的内旋转进行的研究表明，在所有这三种化合物中，该部分保持与苯基异氰酸酯中几乎相同的取向（相对于对位倾斜约140 - 145度）。已确定了相对于取代基NCO和CH₃的两种构象异构体，顺式和反式：对于每种化合物，顺式构象比反式构象高出不到每摩尔一千卡路里。
