Gas-Phase Electron-Transfer Equilibrium Studies on Tetraalkylhydrazines: Geometry Effects on Ionization Thermochemistry, Relaxation Energies, and Ion Solvation Energies

Article abstract of DOI:10.1021/ja00232a001

Equilibrium constants for electron-transfer equilibration between 35 pairs of tetraalkylhydrazines and their cation radicals were measured by high-pressure mass spectrometry and provided the data allowing calculation of aIP and ΔS⁰ of ionization for 31 tetraalkylhydrazines.Photoelectron spectroscopy measurements of vIP allow calculation of their enthalpies of relaxation, which range from a highest value of 38.3 kcal/mol for the trans-dipseudoequatorial conformation of 1,2-dimethylpyrazolidine (19) to a low of 18.9 kcal/mol for bridgehead anti-diazasesquinorbornane (30).The effects of changeing alkyl groups on both vIP and aIP are discussed.Comparison of the gas-phase equilibrium constants (extrapolated to 25 deg C) with cyclic voltammetric measurements of E⁰' in solution show that the enthalpy of solvation is strongest for the compounds with the smallest alkyl groups, tetramethylhydrazine (1) and (19), and about 7 kcal weaker for 30 but that the change in solvation energy correlates with the gas-phase charge-delocalizing ability of the alkyl groups and not with ease of approach of solvent molecules to the nitrogen atoms.