Rates of proton transfer, acid dissociation constants, and the strengths of intramolecular hydrogen bonds in 8-methoxy-NN-dimethyl-1-naphthylammonium ion and 8-hydroxy-NN-dimethyl-1-naphthylamine

Abstract

The rate coefficients for proton transfer from 8-hydroxy-NN-dimethyl-1-naphthylamine in 80%(v/v) dimethyl sulphoxide–water and from 8-methoxy-NN-dimethyl-1-naphthylammonium ion in aqueous solution are respectively 10⁴ fold and 20–50 fold lower than expected for normal proton transfers from a hydroxy- and protonated amino-group. The low rates are due to intramolecular hydrogen bonds in the acids and by comparison with results for protonated 1,8-bis(dimethylamino)naphthalene, the rates show that in this series of peri-substituted naphthalenes the order of hydrogen bond strengths is [graphic omitted]–H ⋯ O < O–H ⋯ N < [graphic omitted]–H ⋯ N. The intramolecular hydrogen bonds also account for the unusual acidities: 8-methoxy-NN-dimethyl-1-naphthylammonium ion (pK 7.75) is a weaker acid by three pK units than NN-dimethyl-1-naphthylammonium ion and 8-hydroxy-NN-dimethyl-1-naphthylamine (pK ca. 14.9) is six pK units weaker than 1-naphthol.