Theoretical Enthalpies of Formation of CHmCln:  Neutral Molecules and Cations

Ab initio molecular orbital calculations have been performed on all possible neutral molecules and cations of the type CH m Cl n ( m + n = 1−3). Equilibrium structures were optimized using gradient techniques at HF/6-31G(d,p), MP2/6-311G(d,p), QCISD/6-311G(d,p), and MP2/6-311++G(d,p). Thermochemical properties (standard enthalpies of formation, adiabatic ionization energies, and proton affinities) have been calculated at QCISD(T)/6-311++G(3df,3pd)//MP2/6-311++G(d,p) and QCISD(T)/6-311G(2df,p)//QCISD/6-311G(d,p), both including core-electron correlation, and at MP4SDTQ/6-311G(2df,p)//MP2/6-311G(d,p), frozen core. Calculations at the first level of theory are accurate to ±1.0 kcal mol -1, and at the second and third levels of theory, to ±2.3 kcal mol -1 . Recent experimental data are critically reviewed against these calculated results, and theory indicates that some experimental values are incorrect. Calculated QCISD(T)/6-311++G(3df,3pd) values for the enthalpies of formation for CCl + and CHCl + are 304.9 and 286.7 kcal mol -1, respectively, and the ionization energies for CCl and CHCl( 1 A‘) are 8.70 and 9.10 eV. Recent experimental results for the enthalpies of formation for CCl 2 (56.5 ± 3.0 kcal mol -1 ) and CCl 3 + (202.2 ± 0.8 kcal mol -1 ) are validated. A hydride affinity scale for chlorinated carbocations, calculated at the MP4SDTQ/6-311G(2df,p) level, gives the relative affinity order to be CCl 3 + ≈ CCl + < CHCl 2 + < CCl 2 + < CH 2 Cl + < CHCl + < CH 3 + < CH + < CH 2 + .