Nonbonded Potential Parameters Derived from Crystalline Hydrocarbons

The previously described least‐squares derivation of nonbonded potential parameters from crystalline aromatic hydrocarbons was extended to include nonaromatic hydrocarbons. Further evidence was obtained that no specially large energy effects are present in the aromatic crystal structures with their π‐electron systems. A better separation of the nonbonded energy into C···C, C···H, and H···H components was obtained when the observational equations for the aromatic and nonaromatic structures were combined. The potentials obtained from the combined observational equations gave better fits to the nonaromatics than to the aromatics. Evidence is presented favoring an H–C–H angle of less than 106° in crystalline n‐pentane and n‐hexane. The parallel packing of molecular chains in the n‐hexane crystal and the nonparallel packing in the n‐pentane crystal were reproduced by a steepest descent minimization of the lattice energy using the observed lattice constants.

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