A theoretical study of the electronic structure of the prototypical zinc carbenes and zinc stannylenes ZnXH(2) (X = C, Sn) as well as their monopositive and dipositive ions ZnXH(2)(+) and Z(n)XH(2)(2+) is reported. Based on ab initio Hartree-Fock calculations and introducing electron correlation through second-order Moller-Plesset perturbation theory (MP2), the molecular structures of ground and some excited states of these complexes have been examined. Special attention has been devoted to the analysis of the bond mechanisms between zinc and carbon or tin and how the charge modifies these bonds. Zn-X stretch force constants and dissociation energy profiles are also reported. In the last part of the work an approach to the ZnCH2-HZnCH photolytic rearrangement has been performed. Based on complete active space self-consistent-Field (CASSCF) calculations a saddle point on the potential energy hypersurface has been located. A careful analysis of the nature of the wave functions for the 10 lowest states suggests a mechanism involving an excitation toward the first B-3(1) excited state lying at 33000 cm(-1) in agreement with experiment (<35700 cm(-1)).