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

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.