Bonded and nonbonded interactions in saturated hydrocarbons

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Abstract
The enthalpy of formation (ΔH°f) of an alkane is expressed as a linear function of eight structure parameters (N) that are essential in characterizing stable conformations of the molecule. Using the least squares criterion, energy parameters (X) which correspond to the linear coefficients of the structure parameters are calculated from experimental ΔH°f. For acyclic alkanes and polycyclic alkanes with six-membered rings, 80 liquids and 63 gases are used. The mean and root-mean-square deviations between the calculated and experimental ΔH°f are, respectively, ±0.18 and ±0.24 kcal mole−1 for liquids and ±0.20 and ±0.28 kcal mole−1 for gases. The resulting energy parameters may be used for predicting the unknown ΔH°f of higher alkanes and for estimating enthalpy differences between certain conformers. For the latter application, those involving the 1,4 and 1,5 interactions represented by the gauche CCCC (XG), gauche–gauche prime CCCCC (XV), and anti–anti CCCCC (XW) interactions are particularly useful. The energy parameter for ring strain (XR) appears necessary for bringing the predicted ΔH°f of gaseous adamantane and diamantane into reasonable agreement with available experimental data.

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