Additive bond-energy scheme with geminal H-H terms Applications to the enthalpies of formation of alkane derivatives

Abstract

The additive bond-energy scheme with geminal H–H terms, previously applied to hydrocarbons and alkyl radicals, has been extended to aliphatic alcohols, ethers, thiols, thioethers, amines, aldehydes and ketones, halogenoalkanes and alkanenitriles. Apart from C–X (X=O, N, S, Cl, Br, I, CN), X–H (X=O, N, S) and CO terms, it is necessary to introduce an additional C–C term where either carbon atom is attached to an atom of significantly higher electronegativity (O, N, Cl), or to a carbonyl group. It is also necessary to adopt a different geminal H···H term for CH ₂ X groups. For alkanols, the anomalous methylene increment can be incorporated by postulating a linear dependence of the H···H term in RCH ₂ OH on the chain length. The agreement between calculated and experimental enthalpies of formation is slightly inferior to that obtained by the Allen method, but requires fewer parameters. A number of experimental enthalpies of formation are identified as being worthy of replication.