Chemistry Test Organic Chemistry 3 — Questions and Answers
Question 1: Which reaction mechanism involves formation of a carbocation intermediate followed by attack of a nucleophile?
- SN2
- SN1 (Correct answer)
- E2
- Radical addition
Correct answer: SN1
SN1 is a two-step process: ionization forms a carbocation intermediate, then the nucleophile attacks.
Question 2: In Markovnikov addition of HBr to propene, which carbon receives the bromine?
- C-1 (terminal carbon)
- C-2 (internal carbon) (Correct answer)
- Both carbons equally
- Neither; Br adds to H
Correct answer: C-2 (internal carbon)
Markovnikov's rule states that H adds to the less substituted carbon and Br adds to the more substituted (C-2) carbon.
Question 3: Which functional group is characterized by a carbonyl carbon bonded to an —OH group?
- Aldehyde
- Ketone
- Ester
- Carboxylic acid (Correct answer)
Correct answer: Carboxylic acid
A carboxylic acid has the structure R–C(=O)–OH, with both a carbonyl and a hydroxyl on the same carbon.
Question 4: What is the product of catalytic hydrogenation of an alkyne using a Lindlar catalyst?
- Alkane
- Trans-alkene
- Cis-alkene (Correct answer)
- Cycloalkane
Correct answer: Cis-alkene
Lindlar catalyst (Pd/CaCO₃ with quinoline) delivers H₂ to the same face (syn addition), producing the cis-alkene.
Question 5: A compound has a molecular formula of C₆H₁₂. How many degrees of unsaturation (index of hydrogen deficiency) does it have?
- 0
- 1 (Correct answer)
- 2
- 3
Correct answer: 1
IHD = (2×6 + 2 − 12)/2 = (14−12)/2 = 1, indicating one ring or one double bond.
Question 6: Which of the following amino acids contains a sulfur atom in its side chain?
- Glycine
- Alanine
- Cysteine (Correct answer)
- Valine
Correct answer: Cysteine
Cysteine has a thiol (–SH) group in its side chain, which can form disulfide bonds important in protein structure.
Question 7: What type of reaction forms a peptide bond?
- Aldol condensation
- Nucleophilic acyl substitution (Correct answer)
- Electrophilic addition
- Radical chain reaction
Correct answer: Nucleophilic acyl substitution
Peptide bond formation is nucleophilic acyl substitution where the amine nitrogen attacks the carbonyl of an amino acid.
Chemistry Test Organic Chemistry 3
Which reaction mechanism involves formation of a carbocation intermediate followed by attack of a nucleophile?