OAT 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)
- K2Cr2O7/H2SO4
- Jones reagent
Correct answer: PCC (pyridinium chlorochromate)
PCC oxidizes primary alcohols to aldehydes and stops there because it is used in anhydrous conditions.
Question 2: In an E2 elimination reaction, the leaving group and the β-hydrogen must be in what geometric relationship?
- Syn-periplanar (0°)
- Gauche (60°)
- Anti-periplanar (180°) (Correct answer)
- Orthogonal (90°)
Correct answer: Anti-periplanar (180°)
E2 requires a concerted anti-periplanar arrangement so the base, β-H, Cα, and leaving group are all coplanar.
Question 3: What is the product when benzene reacts with Cl2 in the presence of FeCl3?
- Cyclohexyl chloride
- Chlorocyclohexadiene
- Chlorobenzene (Correct answer)
- Benzyl chloride
Correct answer: Chlorobenzene
FeCl3 activates Cl2 as an electrophile, enabling electrophilic aromatic substitution to give chlorobenzene.
Question 4: Which of the following molecules exhibits optical activity?
- 2-butanol (Correct answer)
- 2-butanone
- 1-butanol
- Butane
Correct answer: 2-butanol
2-Butanol has a chiral center (C2 bonded to OH, H, CH3, and C2H5), making it optically active.
Question 5: Which functional group is introduced when a terminal alkyne reacts with water in the presence of H2SO4 and HgSO4?
- Alcohol
- Aldehyde
- Ketone (Correct answer)
- Ether
Correct answer: Ketone
Markovnikov addition of water to an internal position of a terminal alkyne forms a methyl ketone via an enol intermediate.
Question 6: The reaction of an ester with excess Grignard reagent yields which product?
- A primary alcohol
- A secondary alcohol
- A tertiary alcohol (Correct answer)
- A ketone
Correct answer: A tertiary alcohol
Two equivalents of Grignard reagent add to an ester—the first forms a ketone intermediate that reacts with the second—yielding a tertiary alcohol.
Question 7: Which of the following is the strongest acid?
- Ethanol (pKa ≈ 16)
- Acetic acid (pKa ≈ 4.75) (Correct answer)
- Phenol (pKa ≈ 10)
- Water (pKa ≈ 15.7)
Correct answer: Acetic acid (pKa ≈ 4.75)
Acetic acid has the lowest pKa (~4.75), meaning it donates a proton most readily due to resonance stabilization of the acetate anion.
OAT Organic Chemistry 2
Which reagent converts a primary alcohol to an aldehyde without over-oxidizing to a carboxylic acid?