DENSITY-FUNCTIONAL THEORY STUDY OF VIBRATIONAL-SPECTRA .6. ASSIGNMENTOF FUNDAMENTAL VIBRATIONAL FREQUENCIES OF BENZENE ISOMERS - DEWAR BENZENE, BENZVALENE, TRIMETHYLENECYCLOPROPANE, PRISMANE, AND 3,4-DIMETHYLENECYCLOBUTENE

The molecular structure and vibrational spectra of Dewar benzene, benz valene, trimethylenecyclopropane, prismane and 3,4-dimethylenecyclobut ene have been investigated by density functional theory using Becke's exchange with Lee-Yang-Parr's correlation functionals and the 6-31G b asis set. Both the calculated structural parameters and vibrational fr equencies are in good agreement with available experimental data. On t he basis of the agreement between the calculated and experimental resu lts, assignments of fundamental vibrational frequencies of Dewar benze ne, benzvalene, and trimethylenecyclopropane were examined and some re assignments are proposed. The calculations also predict prominent IR a nd Raman spectral features of prismane and 3,4-dimethylenecyclobutene, which can assist experimental identification of these compounds and t he assignment of observed spectral features when they are available. ( C) 1997 Elsevier Science B.V.