THE SIGMA-INDUCTIVE EFFECTS OF C=C AND C-C BONDS - PREDICTABILITY OF NMR SHIFTS AT SP(2) CARBON IN NONCONJUGATED POLYENOIC ACIDS, ESTERS AND GLYCERIDES

The C-13 NMR shift separations in a wide range of non-conjugated polye noic acids can be reliably predicted from the sigma-inductive theory d eveloped previously for monoenes, with only one further adjustable par ameter, the dipolar effect of one double bond upon another. Further im provements 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 gai n approximately double. The theory also semi-quantitatively explains t he small differences in carbonyl shift, used in the quantitative analy sis of glycerides.