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D-Glucose (an aldohexose with structure CHO-(CHOH)4-CH2OH) is treated with NaBH4. How many optically active isomers of the product are possible?

1. 1
2. 2
3. 4
4. 8

Correct answer: 2

Solution

Reduction of the aldehyde of D-glucose gives D-glucitol (sorbitol), which is optically active. Among all possible hexitol stereoisomers from this structure, there are optically active pairs. Since starting from D-glucose gives one specific optically active product, and asking for possible optically active isomers of the product type yields 2 (the D and L enantiomeric pair that includes sorbitol).

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