Infrared intensities as a quantitative measure of intramolecular interactions. Part XXV. Interaction between substituents in para-disubstituted benzenes

Abstract

The relation of ν₈ i.r. intensities (including previously unpublished data) for para-disubstituted benzenes to σ°_R constants is considered in the light of: (i) statistic analysis assuming no interaction between substituents of the same electronic nature; (ii) differences between ¹⁹F n.m.r.-and i.r.-determined σ°_R values; (iii) rotational barriers; (iv) theoretical analysis including measurement of deuteriated derivatives; and (v) the variable demand interaction approach developed by Blagdon. Through-conjugation in para-disubstituted benzenes is treated quantitatively in terms of interaction between donor and acceptor groups. Previous work is reassessed. Mixing occurs between ν₈ and ν_NO2 in para-substituted nitrobenzenes.