13C n.m.r. studies. IX. Carbonyl carbon shieldings of some cyclopropyl ketones

Abstract

The 15.1 Mc/s ¹³C nuclear magnetic resonance spectra of 15 aliphatic and alicyclic ketones having a three-membered ring alpha to the carbonyl group have been obtained and the shieldings of their carbonyl carbon nuclei are reported. A number of derivatives of bicyclo-[4.1.0]heptan-2-one, bicyclo[3.1.0]hexan-2-one, spiro[2.5]octan-4-one, and spiro[2.4]heptan-4-one have been included. The primary objective was to investigate the question of conjugation of the cyclopropyl ring with a carbonyl grouping, since we had shown previously that ¹³C shieldings of carbonyl carbons are significantly affected by conjugative interactions. The ¹³C data for several related compounds were obtained to aid in our assessment of the cyclopropyl results. Some evidence of cyclopropyl conjugation is presented.