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Postby MCAT_Retaker » Sun May 20, 2018 4:54 am

Diagnostic Test

How come the answer is not the carbonyl carbon. can you please elaborate.
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Re: Tests

Postby Administrator » Wed May 23, 2018 9:11 am

The explanation brings up two factors that you commonly need when analyzing O-chem problems on the MCAT - steric hindrance and electron density.

That is, the MCAT doesn't often want you memorizing every single step of complex organic mechanisms. Instead, stick with general principles. A common one is just the fundamental definitions - in this case, it asks about a nucleophile. A "nucleophile" is something that loves positive charge (hence the name). That means that it's negatively charged.

So right off the bat, we can eliminate choices B and D since they would be slightly positively charged. Carbons attached to more electronegative atoms tend to have a slight positive charge.

Choosing between the oxygens listed in choice A and choice C, we turn to the other principle listed - steric hindrance. If there's other stuff in the way, it's harder to carry out a reaction. Here, the -OH that's hanging out on the right side of the molecule is less hindered.

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