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MCAT Organic Question — Cram’s Rule

When an optically inactive reagent and a racemic mixture of an optically active compound are mixed, it can create an optically active product from an initially optically inactive set of reagents. Such a process was described by Donald Cram when formulating Cram’s rule when mixing 2-phenylpropionaldehyde and bromobenzene.


This process can best be described as:

A) Electrophilic substitution

B) Nucleophilic substitution

C) Racemization

D) Enantioinduction




The question presents a lot of information but we can clarify our understanding by focusing on the basic process described: an optically inactive thing became an optically active thing. We have no reason to suppose that this process must (or ever) does involve substitution reactions, so we can eliminate (A) and (B). Next, we know that a racemic mixture is optically inactive. So “racemization” would be the opposite of what’s being described in the question. Thus, by process of elimination (D) is the right answer.

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