An ab initio molecular orbital study of the conformational energies of 2-alkyltetrahydro-2H-pyrans (tetrahydropyrans, oxacyclohexanes, oxanes)

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

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

Ab initio Hartree-Fock and Density Functional Theory calculations were used to obtain the geometries and relative energies of the rotamers in the chair conformations of 2-alkyltetrahydro-2H-pyrans and 2- (trimethylsilyl)tetrahydro-2H-pyran. The MP2/6-31G*//6-31G* conformational energies (-ΔG°or A values, kcal/mol) of the 2-alkyltetrahydro-2H-pyrans (Me = 3.18; Et = 3.04; i-Pr = 3.03; t-Bu = 7.56; neo Pent = 2.84) and 2- (trimethylsilyl)tetrahydro-2H-pyran (SiMe3 = 4.77) are larger than those calculated for the corresponding alkylcyclohexanes and 2-alkyltetrahydro-2H- thiopyrans (tetrahydrothiopyrans, thiacyclohexanes, thianes). Plots of the calculated conformational energies for the 2-substituted tetrahydro-2H-pyrans versus the calculated -ΔG°values for the corresponding alkylcyclohexanes (slope = 1.34 and r = 0.983) and for the corresponding 2-substituted tetrahydro-2H-thiopyrans (slope = 2.01 and r = 0.986) are linear. (C) 2000 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)19-39
Number of pages21
JournalJournal of Molecular Structure: THEOCHEM
Volume496
Issue number1-3
DOIs
StatePublished - 7 Jan 2000

Keywords

  • Conformational energies
  • Hyperconjugative orbital interactions
  • Oxacyclohexanes
  • Rotamers
  • Stereoelectronic effects

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