Ring-Chain Tautomerism of Pseudooxynicotine and Some Other Iminium Compounds.

Abstract
The ring-chain tautomerism in aqueous solution of the nicotine metabolite pseudooxynicotine (1) was studied. Of the 4 possible forms of 1, only the chain form and the iminium form could be observed by NMR spectroscopy. The chain form was strongly preponderant at high or low pH. The proportion of the iminium form reached a maximum level of 52-53% in a neutral solution of 1. These results differ strongly from those published by other workers. Some analogous compounds were also investigated.