Theoretical study of tautomerization and isomerization of methylamino- and phenylamino-substituted cyclic azaphospholines, oxaphospholines and thiaphospholines in gas and aqueous phases

Results of B3LYP/6-31+G(d,p) calculations are reported. Special emphasis is put on the effect of the environment on relative stability and structures of different isomers and tautomers of methylamino- and phenylamino-substituted cyclic azaphospholine, oxaphospholine and thiaphospholine in gas and aqueous phases. In the gas phase, the imino forms are found to be the most stable species for the cyclic azaphospholines and thiaphospholines, whereas for oxaphospholines, the amino species are predicted to be more stable. The calculations in the aqueous media were done by considering two different models, i.e., the PCM–SCRF and the Microsolvated/SCRF model. It is found that solvation shifts the stability towards the amino forms, except for the phenyl-substituted cyclic azaphospholine and thiaphospholine, for which the imino forms are more stable in solution. The molecular geometries change only little when going from the gas phase to the aqueous phase. The stability in gas phase and in PCM–SCRF is attributed to the presence of intramolecular hydrogen bonding. In the Microsolvated/SCRF model, the presence of intermolecular hydrogen bonds affects the relative stability of tautomers and isomers.