An ab initio molecular orbital theory study of the conformational free energies of 2-methyl-, 3-methyl-, and 4-methyltetrahydro-2H-pyran

F. Freeman, M. L. Kasner, W. J. Hehre

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Abstract

Ab initio molecular orbital theory with the 6-31G(d), 6-31+G(d), 6-31G(d,p), 6-311G(d,p), 6-311+G(d,p), 6-31G(2d), 6-311G(2d), and 6-311G(2d,p) basis sets have been used to calculate the conformational enthalpies (ΔH°), entropies (ΔS°), and free energies (ΔG°) of the axial and equatorial conformers of 2-methyl-, 3-methyl-, and 4-methyltetrahydro-2H-pyran (tetrahydropyran, oxacyclohexane, oxane) and methylcyclohexane (toluene). Although HF and MP2 generally gave higher conformational free energies (ΔG°) than the experimentally reported values, other MP2 calculations gave ΔG° values in excellent agreement with experimental results for methylcyclohexane [6-311G(d 311G(d,p)] and 3-methyltetrahydro-2H-pyran [6-31+G(d), 6-311+G(d,p)]. Consistent with solution studies, the MP2 calculations gave larger ΔG° values for 4-methyltetrahydro-2H-pyran than for methylcyclohexane.

Original languageEnglish
Pages (from-to)19-26
Number of pages8
JournalJournal of Molecular Structure: THEOCHEM
Volume574
Issue number1-3
DOIs
StatePublished - 16 Nov 2001

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Keywords

  • Ab initio molecular orbital theory
  • Conformational free energies
  • Methyl tetrahydro-2H-pyrans
  • Methylcyclohexane (Toluene)
  • Repulsive nonbonded interactions

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