Proton transfer processes in selenourea: UV-induced selenone → selenol photoreaction and ground state selenol → selenone proton tunneling

摘要

Infrared spectrum of selenourea isolated in low temperature Ar matrix indicates that monomers of this compound adopt exclusively the selenone tautomeric form. UV irradiation (λ > 345 nm) of matrix-isolated selenourea leads to generation of the selenol tautomer (isoselenourea). Two conformers of the selenol tautomer with imino N-H bond oriented anti or syn with respect to the Se-H group were photoproduced. For the matrix kept at 10 K and in darkness, a proton tunneling transforming the photoproduced selenol anti form back into the initial selenone tautomer was observed. The time constant of this process was 16 h. The asymmetric barrier for the selenol → selenone proton tunneling was estimated at MP2/6-311++G(2d,p) level to be as high as 95 kJ mol~(-1) (7940 cm~(-1)). The relation between the height of the barrier and the time constant of proton tunneling was discussed by comparing the current case with that previously studied for thiourea [J. Phys. Chem. A 107 (2003) 6373].