Studies on the C–H/C–D Exchange in Imidazolium (Pilocarpinium) and in 2‐ and 4‐Hydroximinomethyl Pyridinium Compounds

Abstract

The H-D exchange of methylene protons in a side-chain when situated between a positively charged N-atom (a-CH,) and a ketone function was studied in various pilocarpinium (N-methyl imidazolium) and hydroximinomethyl pyridiniums using NMR measurements. Structural factors which determine the course of the exchange are reported, and the role of the solvent was examined. Mass-spectra of nondeuteria ted and deu teriated 4-hydro ximinomethyI-I-phenacyI-pyridinium chloride confirmed the fast exchange of the a-CH,. An alternative H-D exchange of the C, -H in the imidazolium moiety of certain pilocarpinium compounds without a ketone in the N-chain was detected. Mechanisms for the two types of exchanges involving an ylid as intermediate and attack of a deuteron were proposed.