A scaled quantum mechanical reinvestigation of the vibrational spectrum of toluene

A recent investigation and assignment of the IR spectrum of liquid toluene between 400 and 4000 cm(-1) by Keefe and coworkers [J.E. Bertie, Y. Apelblat, C.D. Keefe, J. Mol. Struct. 750 (2005) 78] has been reexamined theoretically using the scaled quantum mechanical (SQM) force field method. it is proposed that three bands - a weak, broad shoulder at 947 cm(-1) assigned as a combination band, an unassigned feature at 1467 cm(-1) and a medium broad band at 2979 cm(-1), also assigned as a combination band - are all in fact fundamentals. Agreement with the remaining assignments is excellent, with an average deviation between the observed and theoretically predicted vibrational fundamentals of just 5.28 cm(-1). The overall intensity pattern of the experimental spectrum is also well reproduced. Analysis involving free rotation of the methyl group and interpretation of the vibrational spectrum in terms of C-2v symmetry for the phenyl ring and C-3v for the methyl group very likely contributed to the experimental misassignments. (C) 2008 Elsevier B.V. All rights reserved.