G2 and G3 Calculations of Enthalpies of Hydrogenation, Isomerization, and Formation of Bi-, Tri-, and Tetracyclic C₇ Hydrocarbons:  The Norbornadiene Cycle

We have calculated the standard enthalpies of isomerization, hydrogenation, and formation (Δ hyd H 298, Δ isom H 298, and Δ f H 298 ) of norbornadiene, quadricyclane, norbornene, nortricyclane, and norbornane by the G2, G2(MP2), G2(MP2,SVP), G3(MP2), and B3LYP/6-311+(3df,2p) procedures. Comparison with combustion and hydrogenation thermochemical results shows that agreement between G- n theory and experiment remains within the target interval of 1 to 2 kcal mol -1 for these C 7 hydrocarbons, but that B3LYP/6-311+(3df,2p) results do not fall within this range.