Organic Stereochemistry Question (From Full Length)

[stester77s]

The correct answer choice is B.

This is my confusion:

Can someone please explain how the molecule only produces one enantiomer only? It seems like it could attack on either side equally. Why does water approach on only one side of the molecule? The H gets attached first, then the OH on the other side, right? Shouldn't the H be able to attack on any side at first, bottom or top? And then consequently the OH would get attached on the other side. But since the H could get attached on either carbon, top or bottom, then consequently a racemic mixture should be produced. Where is my logic faulting?


What does it mean the water approaches from only one side. Why, if the molecule is identical at both carbons?

Thanks!

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[chenzt]

Because of the enzyme, fumerase. It's active site probably can only allow the formation of one stereoisomer, and therefore, water can only have a very specific way of attacking the molecule (water can approach from only one side).