Infrared studies of tautomerism in 2-hydroxypyridine 2-thiopyridine and 2-aminopyridine.

The infrared spectra of 2-hydroxypyridine (2-OHP), 2-thiopyridine (2-SHP), and 2-aminopyridine (2-NH2P) have been recorded in the solid, liquid and vapor phases in the region 4000-200 cm(-1). To support the work, deuterated forms of these compounds in the functional groups XH and NH with (X=O, S, NH) were recorded for the solid and liquid phases. The results show existence of each compound as an equilibrium mixture of two tautomers in monomeric and cyclic dimeric forms in the solid, liquid and vapor phases. The monomers are predominant in the vapor phase. Enthalpy differences between the monomeric tautomers and activation energies for their inter-conversion were determined in each phase.