Potential functions and conformations in cycloalkanes

M. Bixon, S. Lifson

Research output: Contribution to journalArticlepeer-review


Energy functions of bending of the C-C-C angle and of twisting of the CH2-CH2 torsional angle have been examined through their effect on calculations of stable conformations and excess enthalpies of all the cycloalkane molecules from C6H12 to C12H24. The total strain energy was expressed as a function of the internal coordinates-bond lengths, bond angles and torsional angles. H-H distances were derived by matrix algebra, and the method of steepest descent was applied. Energy parameters like the bending force constant, the zero-strain value of bond angles, torsional potential barrier, were varied one at a time, and their effect on conformation and strain energy examined. Results have been compared with calorimetric measurements and with Xray and electron diffractions. Enthalpy of translation-rotation-vibration was also considered and found to be significant. Best agreement between calculations and experiment was obtained when the energy parameters were derived from n-alkanes. Thus, the n-alkane bond angle value of 112·7° is preferable to the tetrahedral angle as the zero-strain value; the torsional potential barrier of propane, 3·4 kcal/mole, is preferable to the corresponding value for ethane, 2·8 kcal/mole.

Original languageEnglish
Pages (from-to)769-784
Number of pages16
Issue number2
StatePublished - 1967
Externally publishedYes


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