Enthalpy of Steric Inhibition to Solvation due to tert-Butyl Groups on an Anion Radical

Article abstract of DOI:10.1021/ja00412a004

Electro-spin resonance technique have been utilized to measure the enthalpy of electron transfer from the anion radical of naphthalene (N -. , K + ) to 2-tert-butylnaphthalene (TBN) and from the anion radical of TBN (TBN -. , K + ) to 2,6-di-tert-butylnaphthalene (DTBN) in dimethoxyethane (DME).These endothermic enthalpies of electron transfer were combined with the heat of solvation of the gas-phase anion radical of naphthalene plus the gas-phase potassium cation in DME, the heats of solvation of the neutral hydrocarbons in DME, and the heats of vaporization of the hydrocarbons in a thermochemical cycle to yield the enthalpy of solvation of (DTBN -. ) g + (K + ) g in DME.This enthalpy of solvation is about 17 kcal/mol less exothermic than that for (N -. ) g + (K + ) g and is attributed to the steric inhibition to solvation by the tert-butyl groups on DTBN -. .The enthalpy of solvation of (N -. ) g + (K + ) g (-162 kcal/mol) was determined by combining the enthalpy of the reaction of the DME solvated anion radical with water with a series of well-known constants in a thermochemical cycle.Thus, by utilizing a combination of calorimetric and ESR techniques a complete picture of the thermodynamic parameters controlling the stabilities of the solvated and gas-phase anion radicals of N and DTBN has been generated.