Inductive and field effects in aromatic substitution. Part I. Kinetics of nitration of 4-phenylpyridine and 4-benzylpyridine

Abstract

The rate profiles for the nitration of 4-phenylpyridine and 4-benzylpyridine in aqueous sulphuric acid indicate that these compounds undergo reaction as the corresponding conjugate acids. Partial rate factors are reported and the rate of meta-substitution in the phenyl group is discussed in terms of the field effect of a unit charge placed at the centroid of charge of the pyridyl ring. Comparison with the reactivity of other neutral and positive substrates indicates that the deactivating effect of the protonated pyridyl group accords fairly closely with that expected from this field effect and not at all with that expected from the polarity of the σ-bond to the phenyl ring.