Quantum chemistry studies of far-infrared spectra of aromatic urethanes

Restricted Hartree-Fock and density function calculations (B3LYP), using 6-311++G(d.p), have been used to investigate the far infrared spectra of aromatic urethanes, synthesized on the basis of 2,4-and 2,6-toluene diisocyanate (2,4-TDI, 2,6-TDI), and the spectrum of ethy I phenyl urethane. It is shown, that the region of frequencies of 100-200 cm(-1) is associated primarily with torsional vibrations of methyl groups. For almost all studied urethanes, the bands are observed in the region 385-340cm(-1), which is associated with in plane deformations of angles C-C-N-C, C-O-C and C-N-C of the urethane groups according to the calculations. The bands, observed at 300-320 and 260-280 cm(-1), are assigned to in plane and out of plane deformations of the urethane skeleton, which are mixed with vibrations of methyl group connected to the benzene ring. (C) 2007 Elsevier B.V. All rights reserved.