The factors are reviewed which influence Hofmann degradation of quaternary ammonium salts, particularly in cyclic systems. An examination of the degradation of piperidinium-l-spiFo-1'-pyrrolidinium hydroxide indicates that the olefin-forming elimination can involve either ring with about equal ease, but that the alternative nucleophilic replacement preferentially opens the pyrrolidine ring. Hofmann elimination of 2 : 2'-dimethylpiperidinium-l-spi~o-1 '-pyrrolidinium hydroxide, cycluhexyldimethylcyclupentylammonium hydroxide, and (cy clohexylmethyl) dimethyl( cyclopentylmethy1)ammonium hydroxide proceeds mainly in one direction in each case, yielding respectively 2-methyl-l-pent-4'-enylpiperidine, cyclopentene (with N-cyclohexyldimethylamine) , and methylenecyclohexane [with dimethyl-HOFMANN degradation of quaternary ammonium hydroxides has been extensively investigated, particularly by Ingold and his collaborators1 who concluded that in a bimolecular Hofmann elimination the tendency, because of hyperconjugation, for the most highly alkylated olefin to be formed (Saytzeff rule) is effectively opposed by the reduction in acidity of hydrogen atoms caused by increasing alkylation at the carbon atoms carrying them, owing to electron repulsion by the alkyl groups in the electrical field of the quaternary ammonium pole. Degradation of the ammonium hydroxide (I; R, R', R", and R"' = alkyl), for example, would lead to preferential anion-attack at a methyl rather than at a methylene or methine hydrogen atom. This theory would in general predict formation of the " least substituted olefin " (Hofmann rule t) on degradation of quaternary ammonium salts, but a " least substituted olefin " does not always arise from anion-attack on a hydrogen atom attached to the least alkylated carbon p to the quaternary nitrogen atom; furthermore, it would be illogical to interpret, for example, the observed degradation of cis-and tram-decahydro-l-methylquinoline methohydroxides * Part I, J., 1956,573. A preliminary note on Hofmann fission of heterocyclic bases was published in Chem. and Ind., 1954, 406. Dr. F. E. King's statement made in J., 1954, 3798, footnote, does not accord with my recollection of events or with my interpretation of the facts.t The Hofmann rule in the strictest sense applies to quaternary ammonium salts containing only primary alkyl groups.For summary see the chapter on " Olefin-forming Eliminations " in Ingold, " Structure and Mechanism in