Infrared Intensities as a Quantitative Measure of Intramolecular Interactions. IV.1 para-Disubstituted Benzenes. The v16 Band near 1600 cm

Abstract

The integrated intensities of the v16 vibration for many para-disubstituted benzenes are correlated by the relation APara = 11,800 (πR°l — πR°2)2 + 170. Discrepancies from this relation are interpreted as due to direct interactions between the substituents; such interactions between acceptor and donor substituents are proportional to (π+ — π) values. Halogens other than F act as d-orbital acceptors, and NO2 is found to interact with strong acceptor groups. The relation enables the sign of the resonance effect to be directly determined; ND3+ and NMe3+ groups are shown to be resonance donors. © 1968, American Chemical Society. All rights reserved.