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Computational determination of the enthalpic and entropic contributions to the conformational preference of monosubstituted cyclohexanes. Molecular mechanics, semiempirical and density functional theory methods and ab initio calculations
Author(s) -
MuñozMuñiz Omar,
Juaristi Eusebio
Publication year - 2002
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.544
Subject(s) - cyclohexanes , chemistry , computational chemistry , ab initio , thermodynamics , mndo , density functional theory , stereochemistry , molecule , organic chemistry , physics
Several computational methods [MM2, MM3, PM3, AM1, MNDO, HF/3‐21G(d), HF/6‐31G(d), B3LYP/3‐21G(d), B3LYP/6‐31G(d), MP2/6‐31G(d), etc.] were examined in their efficiency to reproduce the experimentally obtained thermodynamic data for axial ⇌ equatorial equilibria in benzylcyclohexane ( 7 ) and sulfur‐containing derivatives methylthio ( 8 ), methylsulfinyl ( 9 ), and methylsulfonylcyclohexane ( 10 ). While in general, best agreement between the theoretical results and the experimental data was found when electronic correlation was included in fairly robust MP2/6‐31G(d) calculations, for the estimation of conformational parameters in larger systems the use of lower level HF and B3LYP methods is anticipated to afford reliable data at reasonable computing times. In most cases, proper estimation of Δ S ° parameters requires consideration of Δ$S^{\circ}_{\rm mixing}$ , which appears as dominant term for Δ$S^{\circ}_{\rm total}$parameters. It is appreciated that a proper comprehension of the conformational behavior of monosubstituted cyclohexanes requires of satisfactory understanding of the enthalpic and entropic contributions to the conformational free energy difference, Δ G °. Copyright © 2002 John Wiley & Sons, Ltd.