Additive bond-energy scheme for the calculation of enthalpies of formation of hydrocarbons including geminal H–H terms

Abstract

The enthalpies of formation of hydrocarbons can be reproduced satisfactorily by means of an empirical additive bond-energy scheme which includes a term for each H–H interaction in methyl and methylene groups. By assuming that the C—C bond-energy term is constant and equal to the bond energy found experimentally in diamond, the number of adjustable parameters is minimised. The treatment of steric repulsion can also be simplified, so that for C₃–C₈ alkanes (other than those with the most severe steric interactions) experimental enthalpies of formation can be reproduced with a mean discrepancy of only 0.6 kJ mol^–1 with just two adjustable bond-energy parameters and one steric parameter. For alkenes, alkynes, cycloalkanes and benzene derivatives the results are likewise competitive with those obtainable from much more complicated schemes which require more parameters.