CONFORMATIONAL AND ELECTRONIC INTERACTION STUDIES OF α-SUBSTITUTED CARBONYL COMPOUNDS. VI. p-SUBSTITUTED α-PHENYLTHIOACETONES

Abstract

The analysis of the v _co bands in the I. R. spectrum of p-substituted α-phenylthioacetones indicates a cis/gauche rotational isomerism. The slight solvent effect on the α_c/α_g ratios on going from a non polar solvent to a polar one, for the title compounds, as well as the minute sensitivity of the v _co (cis) frequencies on going from electron-attracting to electron-donating substituents are interpreted on the grounds of the Field (F) and Inductive (I) Effects, which act in opposition in the cis rotamer, practically cancelling each other. The decreasing cis/gauche population ratio on going from electron-attracting to electron-donating substituents suggests the Occurrence of the hyperconjugative interaction in the gauche rotamers of the title compounds. The progressive shielding effect on the methylene and carbonyl carbon atoms in the ¹³C NMR spectra, on going from electron-donating to electron-attracting substituents is ascribed at least in part, to the “Reserve Polar Effect”.

Key Words:

• Conformational studies
• electronic interaction
• Reverse Polar Effect
• I.R. spectroscopy
• ¹³C NMR spectroscopy
• p-substituted
• α-phenylthioacetones