Organic thermochemistry at high ab initio levels. 2. Meeting the challenge: Standard heats of formation of gaseous norbornane, 2-norbornene, 2,5-norbornadiene, cubane, and adamantane at the G2 level

Norbornane (1), 2-norbornene (2), 2,5-norbornadiene (3), cubane (4), and adamantane (5) are large molecules for high-order computational studies and are subject to widely different degrees of strain. Ab initio studies at the G2(MP2) and G2 levels provide purely computational values of the standard enthalpies of formation in the gas phase for these compounds. These results are compared to the available experimental data in order to further assess the reliability of the thermochemical data obtained at these (reasonably high) computational levels.