The determination of the COOH substiuent effect for branched carboxylic acids from carbon-13 chemical shifts

The carboxyl substituent effects for branched carboxylic acids have been determined by carbon-13 Fourier ransform nuclear magnetic resonance of eighteen measured and reported branched acids. For α-branched systems the substituent effects are α = 15.3 ppm, β = 2.6 ppm, γ = −1.9 ppm, δ = 0.9 ppm and ϵ = 0.5 ppm. For other branched acids, the determined carboxyl substituent effects are α = 19.2 ppm, β = 2.1 ppm, γ = −1.4 ppm, δ = 0.6 ppm, and ϵ = 0.6 ppm.