Evaluation of the 13C NMR signals of saturated carbons in some long-chain compounds

Abstract

The ¹³C NMR shift values of saturated carbons in long-chain compounds can be mathematically approximated by equations of the kind:

s = –ax^–b + cx^–d + e

which are similar to those for the Lennard–Jones potential. Here s is the chemical shift of a carbon atom and x is the position in the chain of this atom or a functional group influencing its shift value. Equations have been determined for selected saturated carbons of methyl octadecanoate, cis- and trans-octadecenoic acids, methyl cis-octadecenoates, methyl oxo-, methyl hydroxy-, methyl acetoxy- and methyl epoxyoctadecanoates. Excellent correlation of experimental and theoretical data has been achieved (coefficients of determination in most cases >0.99; deviations of calculated shift data from theoretical data in most cases less than 0.1 ppm). These equations can be used for predicting ¹³C NMR shift values of saturated carbons in compounds with long chains.