Gas-phase enthalpies of ionic intermediate compounds can be estimated using a new technique which is based on the analysis of conjugate forms of the compounds. For ionic intermediates, conjugation determines the extent of charge dispersion which is directly related to the thermodynamic stability of an ion. In a simple application, the proposed method estimates the heterolytic bond dissociation energy of alkanes, which can be used to determine the enthalpy of formation of alkyl cations.