INTERNAL-ROTATION IN CONJUGATED MOLECULES - NITROETHYLENE AND NITROBENZENE

Calculations of the barrier and associated one-dimensional torsional potential are reported for internal rotation of the nitro group in nitroethylene and nitrobenzene. In these conjugated molecules, inclusion of electron correlation is shown to be necessary for reliable barrier predictions, in contrast to internal rotation of methyl or ethyl groups. Electron-correlation effects appear to be adequately described by the simplest correlated method, second-order Møller-Plesset perturbation theory. Good agreement is obtained between theory and experiment for the barrier in nitroethylene, but not for nitrobenzene. The origin of this difference is discussed, and it is concluded that the theoretical prediction for nitrobenzene is likely to be more accurate than the current experimental value. © 1990.