An optically active compound having molecular formula C_6H_12O_6 is found in two isomeric forms (A) and (B) in nature. When (A) and (B) are dissolved in water , they show the following equilibrium. underset([alpha]_(D)=111^@)((A))hArr underset(52.2^@)"Equilibrium mixture"hArrunderset(19.2^@)((B)). (i) What are such isomers called ? (ii) Can they called enantiomers ? Justify your answer ? (iii) Draw the cyclic structure of isomer (A).

An optically active compound having molecular formula C_6H_12O_6 is fo

1.	An optically active compound having molecular formula C_6H_12O_6 is found in two isomeric forms (A) and (B) in nature. When (A) and (B) are dissolved in water , they show the following equilibrium. underset([alpha]_(D)=111^@)((A))hArr underset(52.2^@)"Equilibrium mixture"hArrunderset(19.2^@)((B)). (i) What are such isomers called ? (ii) Can they called enantiomers ? Justify your answer ? (iii) Draw the cyclic structure of isomer (A).
Answer» Solution :The optically active COMPOUND having M.F. `C_6H_12O_6` is glucose. It exists in two stereoisomeric forms (A) and (B). For structure. (i) These two isomers which differ in configuration only at the glycosidic carbon are called anomers. The ANOMER (A) with `[alpha]_(D)=111^@` is called `alpha`-D-glucophyranose while the anomer (B) with `[alpha]_(D)=+19.2^@` is called `beta`-D-glucopyronase. Since `alpha`-form is less stable than the CORRESPONDING `beta`-form, therefore , equilibrium mixture consists of approx, `36%` of `alpha`-form and `64%` of the `beta`-form. (ii) Since these anomers are not mirror images of each other, they cannot be called as ENANTIOMERS. (iii) The anomer (A) with `[alpha]_(D)=111^@` is called `alpha`-D-glucopyranose. Its Fisher projection and Haworth structure are given.