The σ-inductive effects of CC and CC bonds: predictability of NMR shifts at sp2 carbon in non-conjugated polyenoic acids, esters and glycerides

Abstract

The ¹³C NMR shift separations in a wide range of non-conjugated polyenoic acids can be reliably predicted from the σ-inductive theory developed previously for monoenes, with only one further adjustable parameter, the dipolar effect of one double bond upon another. Further improvements can be made by allowing the enhanced transmission of charge by an intervening double bond. Shifts in poly-ynes are also predicted, though in this case both the dipolar effect and the transmission gain approximately double. The theory also semi-quantitatively explains the small differences in carbonyl shift, used in the quantitative analysis of glycerides.