AbstractThe 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