THEORETICAL ENTHALPIES OF FORMATION OF CHMCLN - NEUTRAL MOLECULES ANDCATIONS

Ab initio molecular orbital calculations have been performed on all po ssible neutral molecules and cations of the type CHmCln (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, adiaba tic ionization energies, and proton affinities) have been calculated a t 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 a t 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 re sults, and theory indicates that some experimental values are incorrec t. 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), respect ively, and the ionization energies for CCl and CHCl((1)A') are 8.70 an d 9.10 eV. Recent experimental results for the enthalpies of formation for CCl2 (56.5 +/- 3.0 kcal mol(-1)) and CCl3+ (202.2 +/- 0.8 kcal mo l(-1)) are validated. A hydride affinity scale for chlorinated carboca tions, calculated at the MP4SDTQ/6-311G(2df,p) level, gives the relati ve affinity order to be CCl3+ approximate to CCl+ < CHCl2+ < CCl2+ < C H2Cl+ < CHCl+ < CH3+ < CH+ < CH2+.