Carbon-13 NMR spectra and the method for their calculation for long-chain polybranched carboxylic acids and their derivatives

Carbon-13 NMR spectra of 56 long-chain polybranched carboxylic acids their esters, including chloroand acetoxy-substituted derivatives, have been studied. An empirical linear two-parameter equation, relating carbon chemical shifts in α-branched carboxylic acids and their derivatives to the chemical shifts of the corresponding carbon atoms in analogous hydrocarbons, and to the degree of branching at the α-carbon atom, is suggested for the assignment of the signals, where δ_X is the shift in the acid (ester), δ_H the shift in its hydrocarbon counterpart and n the degree of branching. The regression coefficients, A, B and C, are given for X=COOH, COOMe and COOEt. It is shown that with polysubstituted derivatives, the equation may be applied sequentially. The secondary coefficients for the α-substituent then depend on the nature of the substituent X entering the primary equation. The equation may, if necessary, be applied in combination with the additive and structural increments of halogen atoms.