Chemistry Test Organic Chemistry 2 — Questions and Answers
Question 1: Which reagent is used to convert a primary alcohol to an aldehyde without over-oxidizing to a carboxylic acid?
- KMnO₄
- PCC (pyridinium chlorochromate) (Correct answer)
- H₂CrO₄
- LiAlH₄
Correct answer: PCC (pyridinium chlorochromate)
PCC is a mild oxidizing agent that stops oxidation at the aldehyde stage for primary alcohols.
Question 2: What type of isomers have the same molecular formula and connectivity but differ in the spatial arrangement of atoms that are NOT interconvertible by rotation around single bonds?
- Constitutional isomers
- Conformational isomers
- Configurational stereoisomers (Correct answer)
- Tautomers
Correct answer: Configurational stereoisomers
Configurational stereoisomers (including enantiomers and diastereomers) require bond breaking to interconvert.
Question 3: In an E2 elimination reaction, the leaving group and the beta-hydrogen must be in what relationship?
- Gauche
- Eclipsed
- Anti-periplanar (Correct answer)
- Syn-periplanar
Correct answer: Anti-periplanar
E2 elimination requires an anti-periplanar (180°) arrangement of the leaving group and beta-hydrogen for concerted elimination.
Question 4: Which of the following correctly describes a nucleophile?
- An electron-pair acceptor
- A species that attacks electron-rich sites
- An electron-pair donor that attacks electrophiles (Correct answer)
- A Lewis acid
Correct answer: An electron-pair donor that attacks electrophiles
A nucleophile donates an electron pair to an electrophile (electron-poor site) to form a new bond.
Question 5: What product forms when an ester reacts with excess Grignard reagent followed by aqueous workup?
- A primary alcohol
- A secondary alcohol
- A tertiary alcohol (Correct answer)
- A carboxylic acid
Correct answer: A tertiary alcohol
Excess Grignard adds twice to an ester (first to give a ketone intermediate, then again), yielding a tertiary alcohol.
Question 6: Which spectroscopic technique is most useful for distinguishing between cis and trans isomers of alkenes based on coupling constants?
- IR spectroscopy
- Mass spectrometry
- ¹H NMR spectroscopy (Correct answer)
- UV-Vis spectroscopy
Correct answer: ¹H NMR spectroscopy
In ¹H NMR, vicinal coupling constants (J) are ~12–18 Hz for trans and ~6–12 Hz for cis alkene protons.
Question 7: What is the IUPAC name of the compound CH₃CH₂C(=O)CH₃?
- 2-butanone (Correct answer)
- Butanal
- 3-butanone
- Methyl propanoate
Correct answer: 2-butanone
The carbonyl is at C-2 of the four-carbon chain, making this 2-butanone (also called methyl ethyl ketone).
Chemistry Test Organic Chemistry 2
Which reagent is used to convert a primary alcohol to an aldehyde without over-oxidizing to a carboxylic acid?