Gibbs energy, anomeric effect

The most frequently used measure of the anomeric effect is based on the comparison of the stabihty of 2-substituted oxane (tetrahydropyran THP) and cyclohexane. In general, conformational properties of the oxane ring are similar to those of cyclohexane, with dominance of a chair conformation. It is further presumed that steric interactions in oxane are the same as in cyclohexane, with preference for equatorial positions of bulky substituents. The Gibbs energy of the anomeric effect, AG(AEl), can be expressed as the... 

The term A parameter is also used in the literature for the Gibbs energy —AGg. According to the definition in Eq. 7, the anomeric effect AG(AEl) depends on the A value of the substituent, and on the temperature and solvent used in measurement of equilibria in Eq. 7. This definition can be extended to multisubstituted pyran derivatives, and simple, additivity schemes of steric interactions of substituents are used for the estimation ofAG(AEl). 

Axial Preferences and the Gibbs Energy of the Anomeric Effect AG(AE,) (in kJ.moC ) in the 2-Substituted Oxanes ... 

Stable than the anomer. The experimentally observed Gibbs energy difference in water is 1.5 kJ.mol . The difference of 2.3 kJ.mol between the two values represents the magnitude of the anomeric effect AG(AEl). 

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