Return to MCAT® Blog Homepage

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.

Want more MCAT practice?

We’ve got options for every schedule and learning style!

From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.

MCAT is a registered trademark of the Association of American Medical Colleges (AAMC), which is not affiliated with Blueprint.