OAT Organic Chemistry 4 — Questions and Answers
Question 1: Which reagent is used to reduce a carboxylic acid to a primary alcohol?
- NaBH4
- LiAlH4 (Correct answer)
- H2/Pd
- NaBH3CN
Correct answer: LiAlH4
LiAlH4 is a strong enough hydride donor to reduce carboxylic acids all the way to primary alcohols; NaBH4 cannot.
Question 2: What is the IUPAC name of CH3CH2C(=O)CH3?
- 2-butanone (Correct answer)
- 3-butanone
- Butanal
- Methyl propanoate
Correct answer: 2-butanone
The ketone carbonyl is at C2 of a four-carbon chain, giving 2-butanone (also called methyl ethyl ketone).
Question 3: Which of the following best describes the inductive effect of a fluorine atom on an adjacent carboxylic acid?
- Electron donation via resonance, decreasing acidity
- Electron withdrawal via σ-bonds, increasing acidity (Correct answer)
- No effect on acidity
- Electron donation via σ-bonds, decreasing acidity
Correct answer: Electron withdrawal via σ-bonds, increasing acidity
Fluorine's high electronegativity withdraws electron density through σ-bonds, stabilizing the carboxylate anion and increasing acidity.
Question 4: The reaction of an aldehyde with two equivalents of an alcohol in acid gives which product?
- Hemiacetal
- Acetal (Correct answer)
- Ketal
- Ester
Correct answer: Acetal
Two alcohols condense with an aldehyde under acid catalysis to form an acetal with loss of water.
Question 5: Which of these aromatic substituents is an ortho/para director that deactivates the ring?
- –NH2
- –OCH3
- –Cl (Correct answer)
- –NO2
Correct answer: –Cl
Halogens direct ortho/para via lone-pair resonance donation but deactivate the ring by strong inductive electron withdrawal.
Question 6: What distinguishes a constitutional isomer from a stereoisomer?
- Constitutional isomers have the same molecular formula but different connectivity; stereoisomers have the same connectivity but differ in spatial arrangement. (Correct answer)
- Constitutional isomers differ in molecular formula; stereoisomers have the same molecular formula.
- Constitutional isomers are always chiral; stereoisomers are never chiral.
- There is no difference; they are the same concept.
Correct answer: Constitutional isomers have the same molecular formula but different connectivity; stereoisomers have the same connectivity but differ in spatial arrangement.
Constitutional isomers differ in how atoms are connected, while stereoisomers share connectivity but differ in three-dimensional arrangement.
Question 7: Which of the following best characterizes a nucleophile?
- An electron-pair acceptor
- An electron-pair donor (Correct answer)
- A proton donor
- A species that accepts a hydride ion
Correct answer: An electron-pair donor
A nucleophile donates an electron pair to an electrophile, forming a new covalent bond.
OAT Organic Chemistry 4
Which reagent is used to reduce a carboxylic acid to a primary alcohol?