SPECTROSCOPIC EVIDENCE FOR EQUIVALENT-TO-C-H - O INTERACTION IN CRYSTALLINE STEROIDS AND REFERENCE COMPOUNDS

The attractive interaction between =C-H donors and oxygen acceptors is demonstrated for a number of compounds measured as liquid, solid and in non-polar solution. Reference values for the ''free'' (isolated) molecules are derived from gas-phase or solution measurements. Infrared spectral data for the =C-H stretching mode of a series of compounds with geminal-substituted hydroxyl and ethynyl groups, are reported. Both the DELTAnu(S-C) (= nu(CCl4) - nu(solid)) and DELTAnu(T) (= nu300K - nu100K) values are shown to be indicative of the strength of the =C-H...O interaction. For a limited number of steroids an attempt is made to correlate the H...O distance with the frequency shift, DELTAnu(S-C). The steric effect of neighbouring alkyl groups is shown for some cyclohexanol and adamantanol derivatives.