Transannular interactions in difunctional medium rings. Part 3. 13C and 17O nuclear magnetic resonance studies on cyclic amino ketones
Transannular interactions of alkylamino and carbonyl groups in medium rings have been studied by 13C and 17O n.m.r. spectroscopy. In amino ketones with six-, eight-, ten-, and twelve-membered rings 13C and 17O chemical shifts of the carbonyl group are changed up to 11 (13C) or 81 p.p.m. (17O) relative to the signals of the corresponding cycloalkanone. The observed effects, Δδc and Δδo, are linearly correlated and are obviously not only caused by transannular homoconjugation. Therefore, in contrast to i.r. and p.e. spectroscopic data, only qualitative conclusions regarding transannular interactions are possible. Δδc Values of 1-alkylhexahydroazocin-5-ones (2a–d) are linearly correlated with the first ionization potentials of these compounds.