Evans. breit Conformational Analysis: Axial vs Equatorial Reactivity Chem 206 Different reactivity for axial and equatorial substituents SN2 Reactions(Displacement with Ph-S) Axial substituents are more hindered, thus less reactive in many I Acetylation with Ac2O/Py 31 The axial diastereomer is not always slower reacting a Alcohol Oxidation with Cr(6+) k 0.27 32 Acid-catalyzed esterification CO2H The rate-determining step is breakdown of the chromate ester. This is an 0.04 apparent case of strain acceleration Steric Hindrance and steric Assistance CO2H S 0.05 △AG>△A AAG<MAG° ■ Ester Saponification AG For a more detailed discussion of this topic see ElieL, E. L, S H Wilen, et al. (1994). Stereochemistry of Organic Compounds pp 720-726 △△G AGA >AG ref Reference case AGB<△GretMe3C CO2Et H Me3C CO2Et H TS TS Me3C CO2H H TS Me3C CO2H H CO2H CO2H H H H Me OH Me Me OH Me H Me Me Me3C OH H Me3C OH H Me3C OH H Me3C OH H OH H OH H Me3C OTs H Me3C OTs H Evans, Breit Conformational Analysis: Axial vs Equatorial Reactivity Chem 206 The axial diastereomer is not always slower reacting: Different reactivity for axial and equatorial substituents ■ Acetylation with Ac2O/Py k rel 1 0.13 1 0.27 1 0.04 1 0.05 Axial substituents are more hindered, thus less reactive in many transformations k rel ■ Acid-catalyzed esterification k rel k rel ■ Ester Saponification k rel 20 1 ■ Alcohol Oxidation with Cr(6+) 1 3.2 k rel 1 3.36 k rel The rate-determining step is breakdown of the chromate ester. This is an apparent case of strain acceleration ■ SN2 Reactions (Displacement with Ph–S– ) k rel 1 31 GS Reference Case DG ref DG A DGA > DG ref DDG° DDG > DDG° DGB < DG ref DG B DDG° DDG < DDG° Steric Hindrance and Steric Assistance GS GS For a more detailed discussion of this topic see: Eliel, E. L., S. H. Wilen, et al. (1994). Stereochemistry of Organic Compounds pp 720-726