Group additivity methods without group values

The conventional group additivity (GA) formalism may be identically reduced to a stoichiometric and thermochemical analysis of a special class of reactions referred to as GA reactions, that is, reactions that preserve the type and number of groups. Within this approach, the performance (error) of a GA scheme is determined by the stoichiometry and enthalpy changes of the GA reactions. That is, the lower the enthalpy changes of the GA reactions, the better the performance of a GA scheme. Ideally, an exact GA scheme would imply any conceivable GA reaction to be precisely thermoneutral, that is, have a zero enthalpy change. A somewhat surprising result is that, additionally, the performance of GA methods is influenced by a purely stoichiometric factor of GA reactions. These findings do not improve the performance of a given GA scheme. Rather, it is an interpretation that leads to a deeper understanding of the performance of a GA scheme and may be used in designing more accurate GA schemes.