Hydroboration of C70 in toluene yields a 2:1 mixture of 1,9-C70H2 and 7,8-C70H2. Equilibration of these two isomers in the presence of a Pt catalyst reveals a free energy difference of 1.4 ± 0.2 kcal/mol. Whereas semiempirical calculations have been found to predict the energy ordering of many fullerene derivatives incorrectly, ab initio Hartree-Fock (HF) calculations have been found to yield quantitative predictions of experiment. The HF/6-31G* level energy separation of l,9-C70H2 and 7,8-C70H2 of 1.3 kcal/mol is in excellent agreement with experiment. Relative stabilities of isomers of bis(methano)fullerenes were found to parallel those of analogous C60H4 isomers. Density functional theory (DFT) methods have been tested and are equivalent in accuracy to HF methods if similar basis sets are used. C60H2 and C60H4 can be efficiently produced on larger (≥ 50 mg) scales with diimide generated from potassium azodicarboxylate and acetic acid in o-dichlorobenzene.