How many stereoisomers would be expected from a ketohexose?

Question

Quizplus · Accepted Answer

A ketohexose has 6 carbons and a keto group, which means it has one chiral center. The number of stereoisomers is given by 2^n, where n is the number of chiral centers. Therefore, with one chiral center, we have 2^1=2 stereoisomers. However, in this case, we also need to consider the keto group, which introduces a second tautomeric form for each stereoisomer. Therefore, we multiply by 2 again to get a total of 2x2=4 stereoisomers. However, this is only true for linear ketohexoses. If we also consider cyclic forms, which are common for hexoses, the number of stereoisomers increases even further. In fact, if we consider all possible cyclic forms, we can get up to 8 stereoisomers. Therefore, the best answer choice is B, which represents the maximum number of stereoisomers possible.

How Many Stereoisomers Would Be Expected from a Ketohexose