Alkyl substituent effect on the polarity of phenols-tri-n-alkylamine complexes

The formation constants and the dipole moments of the H-bonded adducts of 1:1 and 2:1 stoichiometries formed between three different phenols (phenol, 2,4,6-trichlorophenol, and 2,4-dinitrophenol) and different tri-n-alkylamines are determined in solvents of weak polarity. The polarity of the 1:1 complexes of 2,4,6-trichlorophenol with tri-n-alkylamines markedly increases with increasing degree of amine alkylation, in contrast with the complexes involving the two other phenols. The influence of the basicity and steric hindrance of the tri-n-alkylamines on the proton-transfer constant is discussed and quantitative correlations are deduced.