| Abstract: | Base‐catalyzed H/D‐exchange for α‐ and β‐isophorone ( 1 and 2 , resp.) was monitored by NMR spectroscopy to identify the number and nature of reactive sites. Results show that α‐isophorone ( 1 ) undergoes H/D exchange at up to four different sites depending on reaction conditions. β‐Isophorone ( 2 ), on the other hand, exhibits activity at two sites, predominantly at the α‐position, under comparable conditions. Quantum‐chemical calculations indicate that the thermodynamically more‐stable anions formed upon proton abstraction from isophorone are not favored kinetically in all cases. Thermodynamically unfavorable H/D‐exchange at the α‐position in 1 , which is observed experimentally, is explained via intermediate formation of γ‐isophorone ( 3 ) with subsequent conjugation to the α‐isomer. Differences observed in the reactivities of the two isomers and differences in reactivity of 1 under various conditions in reactions involving proton abstraction as an initial step may be partly explained on the basis of these results. |
