Two intramolecular rearrangement reactions trans-N2H2 --> cis-N2H2 and F2S2 --> FSSF have been studied in both gas and solution phases using the ab initio SCF method at the Hartree-Fock level as well as using density functional theory with B3LYP exchange-correlation functionals with 6-311G** and 6-311++G** basis sets. Polarizability calculations have been performed using Sadlej's basis set also. Maximum hardness and minimum polarizability principles have been found to be valid in almost all cases. For the former reaction, the maximum molecular valency principle is obeyed. Reactions become more favorable, thermodynamically and kinetically, in the presence of the solvent. Variation of electrophilicity along the internal reaction coordinate is analyzed in terms of the profiles of the global electrophilicity index as well as condensed electrophilic Fukui functions at different atomic sites, It is found that electrophilicity decreases in the solution phase.