PCAT Organic Chemistry 5

Question 1

Which of the following correctly ranks carboxylic acid derivatives from most to least reactive toward nucleophilic acyl substitution?

Accepted Answer

Acyl chloride > anhydride > ester > amide

Answer

Reactivity decreases as the leaving group becomes a worse leaving group: Cl⁻ (best) > RCOO⁻ > RO⁻ > NH2⁻ (worst), giving acyl chloride > anhydride > ester > amide.

Question 2

What is the product when an alkene reacts with bromine (Br2) in CCl4?

Accepted Answer

A vicinal dibromide via anti addition

Answer

Br2 adds to alkenes via a bromonium ion intermediate, giving anti addition of two bromine atoms across the double bond to form a vicinal (1,2) dibromide.

Question 3

Which of the following describes the relationship between chair conformers of cyclohexane?

Accepted Answer

Conformational isomers

Answer

The two chair conformers of cyclohexane interconvert rapidly by ring flipping and differ only in conformation, not connectivity, making them conformational isomers.

Question 4

Grignard reagents (RMgX) act as which type of species in organic reactions?

Accepted Answer

Nucleophiles and strong bases

Answer

Grignard reagents are carbanion equivalents that act as strong nucleophiles and bases due to the highly polarized C–Mg bond.

Question 5

What is the role of H2SO4 in the nitration of benzene?

Accepted Answer

It generates the nitronium ion (NO2+) electrophile from HNO3

Answer

H2SO4 protonates HNO3, leading to loss of water and formation of the nitronium ion (NO2+), the active electrophile in EAS nitration.

PCAT - Pharmacy College Admission Test Practice Test

PCAT - Pharmacy College Admission Test Practice Test

PCAT Organic Chemistry 5