Abstract:The gas phase N-and 0-protonation of distorted amides 3,4-dihydro-2-0x0-1.4-ethanoquinoline (la), 3,4-dihydro-2-0x0-l,4-propanoquinoline (lb), 3,3,4,5-tetrahydro-2-0x0-1,5-ethanobenzazepine (lc), and 3,3,4,5-tetrahydro-2-0x0-1,5-propanobenzazepine (16) and normal amides 4-bromo-2,N-dimethylacetanilide (5a) and 2,N-dimethylacetanilide (Sb), along with the N-protonation of benzoquinuclidine (7), has been studied calculationally at the semiempirical level of theory with AM 1. Calculated enthalpies of N-and 0-protonation (proton affinities) indicate that l a , lb, and l c should protonate on nitrogen and Id, 5a, and 5b on oxygen. A satisfactory straight-line relationship between the calculated proton affinities of la, lb, lc, and 7 with experimental solution pK,'s is used to estimate the solution pK, of Id. Results of a calculational study on the gas phase N-and 0 -methylation of lb, lc, and I d are nicely in accord with the findings of an experimental solution phase study of the methylationhydrolysis of l b and Id: while l b methylates on nitrogen, Id methylates on oxygen. A calculational study of possible pathways of hydrolysis of the N-protonated amides indicates that solvolysis of the hydrates of these species represents a viable route for their conversion to ring-opened products.Key words: protonation, methylation, reactions, distorted amides, AM1 calculations.

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