Nine azines bearing F, Cl, Br, CF3, CF2CF3, CH(CF3)2, CHCHCH2, CHCHCH(CH3) and CHCHCH(C6H5) substituents have been theoretically studied at the B3LYP/6-311++G(d,p) level. Concerning the E/Z isomerism, in all cases, the large groups prefer to be “outside” (in general, E), i.e. for conjugated azines the extended conformation (EEEE) is always preferred. In the case of the CH(CF3)2 substituent, the imine–enamine tautomerism has been studied, the imine one being clearly more stable. The differences in energy between the different isomers and conformers have been statistically analyzed.