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.