Half-life of equatorial cyclohexyl chloride at various temperatures

The free-energy difference between conformers is referred to as the conformational free energy, or sometimes as the A value. For substituted cyclohexanes, we wiU follow the convention of specifying the value of -AG° for the equilibrium written as  

Since AG° will be negative when the equatorial conformation is more stable than the axial, a positive value of -AG° is indicative of this condition. 

Conformational free-energy values for many substituent groups on cyclohexane rings have been determined by NMR methods some are recorded in Table 3.5. Conformational free energies measured at low temperatures are not believed to vary much from their values at room temperature. 

The various methods available for determining conformational free energies have been reviewed and compared. Several compilations of conformational free energies are available.  

A tert-butyl substituent experiences a strongly repulsive van der Waals interaction with y/i-axial hydrogens in the axial orientation, and cannot relieve the attendant strain by rotation about the bond to the ring. The conformational free energy of a tert-butyl group has been calculated by molecular mechanics to be 

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Table 3.4. Half-Life of Equatorial Cyclohexyl Chloride at Various Temperatures ... 

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