PCAT Organic Chemistry 2 — Questions and Answers
Question 1: Which reagent converts a primary alcohol to an aldehyde without over-oxidizing to a carboxylic acid?
- KMnO4
- PCC (pyridinium chlorochromate) (Correct answer)
- H2CrO4
- K2Cr2O7
Correct answer: PCC (pyridinium chlorochromate)
PCC oxidizes primary alcohols to aldehydes and stops there because it is a mild oxidant used in non-aqueous conditions.
Question 2: What is the major product when 2-butene undergoes acid-catalyzed hydration?
- 1-butanol
- 2-butanol (Correct answer)
- butanal
- diethyl ether
Correct answer: 2-butanol
Markovnikov addition of water across the double bond of 2-butene places the OH on the more substituted carbon, giving 2-butanol.
Question 3: Which spectroscopic feature is most diagnostic for a carbonyl group (C=O) in IR spectroscopy?
- Broad absorption at 2500–3300 cm⁻¹
- Strong absorption near 1700 cm⁻¹ (Correct answer)
- Sharp absorption at 3300 cm⁻¹
- Absorption near 1000–1100 cm⁻¹
Correct answer: Strong absorption near 1700 cm⁻¹
The C=O stretch appears as a strong, sharp absorption near 1700 cm⁻¹ (exact position varies with functional group).
Question 4: In an E2 elimination reaction, the hydrogen and leaving group must be in what geometric relationship?
- Gauche
- Eclipsed
- Anti-periplanar (Correct answer)
- Syn-periplanar
Correct answer: Anti-periplanar
E2 requires a concerted, single-step mechanism where H and the leaving group must be anti-periplanar (180°) to allow orbital overlap.
Question 5: Which of the following compounds is aromatic?
- Cyclobutadiene
- Cyclooctatetraene
- Pyridine (Correct answer)
- Cyclopentadiene
Correct answer: Pyridine
Pyridine is aromatic because it is planar, fully conjugated, and has 6 π electrons (4n+2, n=1) satisfying Hückel's rule.
Question 6: What type of isomers are D-glucose and L-glucose?
- Constitutional isomers
- Diastereomers
- Enantiomers (Correct answer)
- Conformational isomers
Correct answer: Enantiomers
D-glucose and L-glucose are non-superimposable mirror images, making them enantiomers.
Question 7: Which reaction mechanism involves a planar carbocation intermediate and racemization of the product?
- SN2
- E2
- SN1 (Correct answer)
- E1cb
Correct answer: SN1
SN1 proceeds via a planar sp2 carbocation; nucleophilic attack from both faces leads to racemization.
PCAT Organic Chemistry 2
Which reagent converts a primary alcohol to an aldehyde without over-oxidizing to a carboxylic acid?