Association between polar molecules. Part 1.—Nuclear magnetic resonance study of the dipole association of hexamethylphosphoramide with p-substituted nitrobenzenes

Abstract

Dipole association between hexamethylphosphoramide (HMPA) and p-substituted nitrobenzenes was investigated in non-polar solvents. N,N-dimethyl, O-methyl, methyl and chloro groups were considered as substituents, and carbon tetrachloride and methylcyclohexane were used as solvents. The data are analysed assuming the formation of a 1:1 associate between HMPA and nitrobenzenes. A significant substituent effect on both the equilibrium constant and the induced shift of association is confirmed, and these results are discussed in relation to the dipole moment or the linear combination of the substituent constants σ_i and σ⁺_π.