Comparison of gas and solution phase intrinsic rate constants for electron transfer of tetraalkylhydrazines†

Rate constants for 40 gas-phase electron transfer reactions at 550 K between 22 tetraalkylhydrazines are fitted using Marcus cross rate theory, and compared with previous studies in acetonitrile solution. The relative reactivities are surprisingly similar in the gas phase and in solution. Strong cation-neutral association in the gas phase appears to lessen striking electronic effects previously reported for similar reactions in solution. The relative reactivities of 1,2-dimethylhexahydropyridazine ([6]Me-2) and 1;2-dimethyl-1,2,3,6-tetrahydropyridazine ([u6]Me-2) switch between solution and the gas phase. It is suggested that this may occur because gas-phase ion-dipole complexes are much more tightly bound than are encounter complexes in solution, allowing a conformational change to the more reactive conformation of [u6]Me-2 in the gas phase, but not in solution.