An out-of-plane force field for some benzene derivatives having unsaturated substituents

Abstract

A simplified out-of-plane valence force field has been developed for some benzene derivatives that have unsaturated substituents. The molecules treated in this study are benzene, styrene, benzaldehyde, ethynylbenzene and m- and p-diethynylbenzenes. In the force field we have used two different approximations. The first one includes 27 independent force constants, 12 of which are directly transferred from analogous molecules and 15 optimized on 242 experimental frequencies, giving an rms frequency deviation of 6.69 cm−1. The second and somewhat simpler one deals with 12 transferred and 12 optimized force constants giving an rms deviation of 6.95 cm−1. For comparison a force field for some methyl substituted benzenes has also been derived using the same approximations. The transferability of force constants is discussed in the light of the results achieved. On the basis of the calculations certain revisions in previous assignments have been made.