On quasi-transferable molecular fragments. Part V: Free radicals; the dissociation of organic molecules, an improved Xα(LSD) approach

The new formula for the standard perfect-gas enthalpy of formation, Δ H f ∘ = ∑ K F [ K ] + ZPE + H T - H 0 - ∑ k < l ε kl - ( CNE - E nb ) , originally derived for ground-state molecules, is valid for radicals as well. [ F [ K ] , F [ L ] , … are invariable parameters of hypothetical fragments K, L, etc. linked to one another by bonds with energy εkl between atoms k and l(k ∈ K, l ∈ L, …); ZPE + HT − H0 is the familiar sum of zero-point plus heat-content energy; CNE—the so-called charge neutralization energy—takes care of the fact that the fragments K, L, … are usually not individually electroneutral in the original molecule or free radical, and Enb accounts for interactions between nonbonded atoms.] For any two-fragment radical, εkl + CNE − Enb can thus be obtained from its Δ H f ∘ enthalpy; the latter can be either experimental or, with good accuracy, deduced from LCGTO-Xα(LSD) theory, thus offering a first glance at bonding properties hidden in the interior of free radicals.