2-Chloromethylenecycloheptan- and -octanones: a conformational study by dipole moments, spectroscopy, and nucleophilic reactivity

Abstract

The title compounds were identified as trans-s-cis by their spectroscopic properties and experimental and calculated dipole moments. Their reactions with piperidine in ethanol were studied kinetically at 15–45 °C. Measured rate coefficients for 2-chloromethylenecyclo-octanone are larger than those of the parent seven-membered cyclic compound, the rate ratio being 2–3. The decrease in reactivity as ring size decreases is explained in terms of a diminished degree of conjugation in the vinyl-carbonyl skeleton due to deviation from coplanarity. Further support comes from u.v. and n.m.r. spectra as well as dipole moments. A comparison between the nucleophilic reactivity of s-cis and s-trans derivatives is discussed.