Hydroxytropylium chloride: the first crystal structure of an unfunctionalized hydroxytropylium ion

Abstract

The crystal structure of hydroxytropylium chloride, C7H6OH+·Cl−, the hydrochloride salt of tropone, is described, which represents the first crystallographic characterization of an unfunctionalized hydroxytropylium ion. Crystals were obtained serendipitously from a sample of chlorotropylium chloride after partial hydrolysis. This highlights the role of hydroxytropylium ions as an intermediate in the hydrolytic decomposition of halotropylium halides to tropone. The solid-state structure consists of layers, in which the hydroxytropylium and chloride ions interact via both strong hydrogen bonds formed by the hydroxy protons and weaker hydrogen bonds formed by the tropylium protons to produce a two-dimensional network.