Dipole Moments of some Ortho-Substituted Anilines

Abstract

WE have measured the dipole moments of aniline, N-methyl aniline, N,N-dimethyl aniline, and corresponding toluidines and xylidines. As is seen from the accompanying table, alkylation affects the dipole moments of aniline and p-toluidine to a small extent, the difference in dipole moment between the primary and the tertiary amines being about 0.05 Debye. In the case of ortho-substituted amines, however, the substitution of two methyl groups at the nitrogen atom lowers the dipole moment by about 0.7 Debye. The dipole moments of these tertiary aniline homologues have almost the same value as that of aliphatic tertiary amines, namely, 0.8 Debye1. This result is in good agreement with the result obtained by Thomson2 from measurements of molecular refractivities. He calculated that the atomic refractivity of nitrogen in dimethyl 2,6-xylidine approaches very closely the value for nitrogen in a tertiary aliphatic amine. Furthermore, Remington3 has found from ultra-violet absorption spectra that the resonance is inhibited in ortho-substituted derivatives of dimethyl aniline.