n-π Interaction between an oxygen lone pair and π-electrons in cyclic allylic alcohols and ethers; carbon-13 nuclear magnetic resonance spectra, catalytic hydrogenation, and CNDO/2 calculations

Abstract

In order to elucidate the n-π interaction between an oxygen lone pair and π-electrons, ¹³C n.m.r. spectra have been obtained for several cyclic allylic alcohols and ethers. The chemical shifts for sp²-carbons of these compounds are compared with those of the corresponding hydrocarbons. The chemical shift differences (Δδ) between compounds in which the oxygen atoms are placed at an anticlinal position with respect to the double bond and the corresponding hydrocarbons are different from those of a set of compounds, the oxygens of which are synperiplanar. We have also studied catalytic hydrogenation of and CNDO/2 calculations for these cyclic allylic compounds. These results are discussed in terms of homoconjugation