Collect. Czech. Chem. Commun. 1983, 48, 71-81

Interaction and flexibility of molecules in hydrocarbon aggregates, torsional potential in a group of hexanes

Ján Gajdoš and Tomáš Bleha

Polymer Institute, Slovak Academy of Sciences, 842 36 Bratislava


The molecular-mechanics method has been used for calculation of the torsional potential V(φ) of internal rotation around central C-C bond in hexane with one or two other hexane molecules in the neighbourhood and with full optimization of external and internal degrees of freedom. The optimum energy arrangement of the hydrocarbon molecules has been determined for various values of the φ angle as well as the optimum intramolecular geometry parameters. The adjacent molecules with all-trans conformation accommodate to the shape variation of the rotating molecule by means of translation motion. The adjacent molecules can change substantially the form of V(φ) potential as compared with the isolated molecule, and they increase rigidity of the hydrocarbon chain. For some types of mutual arrangement, however, it has been found that the other molecule in the vicinity decrease the conformational energies and barriers of transitions between the rotation isomers as compared with the isolated molecule. Thus the inter-chain forces can induce also an effective coiling of the chain. Implications of these findings have been discussed with respect to structural properties of various real hydrocarbon aggregates in solution and in solid state.