Charge distributions and chemical effects. X. Enthalpies of formation of alkanes, a calculation from 13C nuclear magnetic resonance shifts

Abstract

An analysis of the molecular energy in terms of bond contributions indicates that the latter (εij) can be approximated by a linear combination of the changes in net charges qi and qj. From the equation ΔH(atomization) = ∑εij, and the relationship between 13C chemical nmr shifts and C net charges, it is then possible to derive a two-parameter equation, ΔHf0 = ΔHf0(C2H6) + ν(N–2) + λ∑(Ncc + 1)δeth, which enables the calculation of enthalpies of formation of alkanes CNH2N+2 from 13C nmr shifts (δeth = shift relative to ethane, Ncc = number of CC bonds formed by the C atom whose shift is δeth).