Enthalpic and Entropic Contributions to the Conformational Free Energies of Methylthio, Methylsulfinyl, Methylsulfonyl, Phenylthio, Phenylsulfinyl, and Phenylsulfonyl [S(O)<i><sub>n</sub></i>R, <i>n</i> = 0, 1, 2; R = CH<sub>3</sub>, Ph] Groups in Cyclohexane
                                
                                    
                                        作者:Eusebio Juaristi、Victoria Labastida、Sandra Antúnez                                    
                                    
                                        DOI:10.1021/jo991181u
                                    
                                    
                                        日期:2000.2.1
                                    
                                    A variable-temperature NMR study of (cis-4-methylcyclohexyl)methyl sulfide (1), sulfoxide (2), and sulfone (3), as well as (cis-4-methylcyclohexyl)phenyl sulfide (4), sulfoxide (5), and sulfone (6) allowed determination of the thermodynamic parameters, Delta H degrees and Delta S degrees, for the title groups. Reproduction of the experimental results with Allinger's MM3 program was successfully accomplished in the case of the sulfoxide and sulfide groups. Nevertheless, modification of the original force field torsional parameters was required in order to adequately reproduce the experimentally observed behavior of the sulfonyl derivatives. Rationalization of the enthalpic and entropic contributions to Delta G degrees [S(O)(n)R, n = 0, 1, 2; R = CH3, Ph] is advanced in terms of the steric characteristics of these sulfur-containing groups and the resulting rotameric populations in the axial and equatorial monosubstituted cyclohexanes.