Vibrational spectra and structure of isopropylbenzene

Infrared spectra (4000–400 cm−1) and Raman spectra (1700–40 cm−1) of the liquid and two crystalline solids of isopropylbenzene (cumene) and isopropylbenzene-d12 have been recorded. The spectra indicate that in the liquid and crystalline solids isopropylbenzene exists in planar conformation only (CH bond is in the plane of the benzene ring). An assignment of the observed band wave numbers both isopropylbenzene and isopropylbenzene-d12 is discussed by comparison with normal mode wave numbers and IR intensities calculated from ab initio 6-31G (d) force fields.