A dipole-moment study of substituted pyrazines and quinoxalines

An attempt has been made to rationalize the dipole moments of 2-chloro-, 2-ethoxy-, 2-ethylthio-, 2-amino-, 2-ethylamino- and 2-diethylamino-pyrazine in terms of substituentring mesomeric effect. In 2-substituted pyrazines, the substituent mainly interacts with the ortho-to-substituent ring-nitrogen atom. Preferred conformations are proposed for 2-ethoxypyrazine and 2-methoxypyridine, 2-ethylthiopyrazine and 2-methylthiopyridine, 2,5-diethoxypyrazine, 2,3-dimethoxyquinoxaline and 2,3-bis(methylthio)quinoxaline. The dipole moments of aminopyridines, amino-s-triazine and methoxy-s-triazine are also interpreted.