Conformational and electronic interaction studies of p-substituted alpha-phenoxyacetones

The nu(CO) analysis of p-substituted alpha-phenoxy-acetones X-phi-O-CH2-C(O )-Me (1-6) indicates the existence of the cis/gauche rotational isomerism. The nearly constant increase in the cis/gauche population ratios for the wh ole series, on going from carbon tetrachloride to acetonitrile, and the sma ll sensitivity of the carbonyl frequency shifts (Delta nu(C)) for the cis r otamer, on going from electron-attracting to electron-donating substituents , are interpreted as an interplay of the Field (F) and the inductive (-I) E ffects, which originates an almost constant carbonyl bond order, and sugges ts that the cis rotamers have almost the same energy in the whole series. T he decrease in the cis/gauche population ratios, in all solvents, and the d eshielding effects on the carbonyl carbon atom, and on the methylene carbon atom in a weaker extent, observed in the C-13 NMR spectra, on going from e lectron-attracting to electron-donating substituents, are discussed in term s of pi*(CO)/n(O) orbital and Ardelta+-Odelta- - Cdelta+=Odelta- Coulombic, interactions, which stabilize the gauche rotamers of the investigated comp ounds.