PCAT Organic Chemistry 3

Question 1

Which of the following best describes the Diels-Alder reaction?

Accepted Answer

Concerted [4+2] cycloaddition between a diene and a dienophile

Answer

The Diels-Alder reaction is a pericyclic [4+2] cycloaddition occurring in a single concerted step between a conjugated diene and a dienophile.

Question 2

What is the product of treating a ketone with NaBH4 followed by aqueous workup?

Accepted Answer

A secondary alcohol

Answer

NaBH4 reduces a ketone (R2C=O) by delivering hydride to the carbonyl carbon, yielding a secondary alcohol after protonation.

Question 3

What does the term 'leaving group ability' depend on most directly?

Accepted Answer

Stability of the leaving group as an anion or neutral molecule

Answer

A good leaving group departs as a stable species (weak base/stable anion), so leaving group ability correlates with stability after departure.

Question 4

Which functional group is produced by the reaction of a carboxylic acid with an amine?

Accepted Answer

Amide

Answer

A carboxylic acid reacts with an amine (with heat or activation) to form an amide (R-CO-NR2) plus water.

Question 5

In NMR spectroscopy, chemically equivalent protons show how many signals?

Accepted Answer

One signal per equivalent set

Answer

Chemically equivalent protons are indistinguishable and appear as a single NMR signal regardless of how many protons are in that set.

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