ESTUDYR
ORGANIC CHEMISTRY 1 REACTIONS – ACS 2025/26 MULTICHOICE
ANSWERED EXAM QUESTIONS WITH DETAILED RATIONALES
1. Which reagent is used to convert an alkane → bromoalkane (radical halogenation)?
A. HBr, ROOR
B. Br₂, UV light
C. NBS, light
D. Br₂, FeBr₃
Rationale: Br₂ under UV initiates radical chain halogenation of alkanes.
2. Which reagent gives alkene → bromoalkane by ionic addition (Markovnikov)?
A. Br₂, CCl₄
B. HBr, 20 °C
C. HBr, ROOR (peroxide)
D. NBS, light
Rationale: HBr adds across C=C to give bromoalkane (Markovnikov unless peroxides
present).
3. Which reagent converts an alkene → vicinal dibromoalkane?
A. HBr
B. HBr, ROOR
C. Br₂, 20 °C (in inert solvent)
D. NBS
Rationale: Br₂ adds across C=C to give vicinal (1,2-) dibromide via bromonium ion.
4. Which conditions hydrogenate an alkene → alkane?
A. Na, NH₃
B. Lindlar catalyst + H₂
C. Ni or Pt catalyst with H₂ gas
D. HBr, ROOR
Rationale: H₂ with metal catalysts (Pd, Pt, Ni) performs catalytic hydrogenation (syn).
5. Which reagent set performs alkene → alcohol via acid-catalyzed hydration?
A. BH₃, H₂O₂
B. OsO₄, NMO
C. H₃PO₄ (or conc. H₂SO₄) and H₂O
D. O₃, DMS
Rationale: Strong acid + water yields Markovnikov hydration to alcohol.
, ESTUDYR
6. Conditions for alcohol → alkene (dehydration)?
A. NaBH₄
B. Conc. H₂SO₄ or Al₂O₃ at high T
C. PCC, CH₂Cl₂
D. OsO₄
Rationale: Acid-catalyzed dehydration (E1/E2 depending on substrate) eliminates water
to form alkene.
7. How to convert bromoalkane → alcohol (nucleophilic substitution)?
A. HBr
B. NaOH (aqueous / SN1 or SN2 depending on substrate)
C. LiAlH₄
D. H₂, Pd/C
Rationale: Hydroxide displaces halide to give alcohol.
8. Which oxidant converts a primary alcohol → aldehyde (stops at aldehyde)?
A. KMnO₄ (aq, hot)
B. H₂CrO₄ (strong)
C. PCC (pyridinium chlorochromate)
D. NaBH₄
Rationale: PCC in nonaqueous solvent oxidizes 1° alcohols to aldehydes without
overoxidation.
9. Which reagent oxidizes a primary alcohol → carboxylic acid?
A. PCC
B. K₂Cr₂O₇ / H₂SO₄ (strong oxidizing acidic conditions)
C. NaBH₄
D. Lindlar catalyst
Rationale: Strong chromium oxidants fully oxidize 1° alcohols to carboxylic acids.
10. Which reagent oxidizes a secondary alcohol → ketone?
A. LiAlH₄
B. NaBH₄
C. K₂Cr₂O₇ / H₂SO₄ (or PCC, CrO₃)
D. H₂, Pd/C
Rationale: Secondary alcohols are oxidized to ketones by common oxidants (chromium-
based or PCC).
11. Which statement about chromic acid (H₂CrO₄) is correct?
A. Mild, stops at aldehydes.
ORGANIC CHEMISTRY 1 REACTIONS – ACS 2025/26 MULTICHOICE
ANSWERED EXAM QUESTIONS WITH DETAILED RATIONALES
1. Which reagent is used to convert an alkane → bromoalkane (radical halogenation)?
A. HBr, ROOR
B. Br₂, UV light
C. NBS, light
D. Br₂, FeBr₃
Rationale: Br₂ under UV initiates radical chain halogenation of alkanes.
2. Which reagent gives alkene → bromoalkane by ionic addition (Markovnikov)?
A. Br₂, CCl₄
B. HBr, 20 °C
C. HBr, ROOR (peroxide)
D. NBS, light
Rationale: HBr adds across C=C to give bromoalkane (Markovnikov unless peroxides
present).
3. Which reagent converts an alkene → vicinal dibromoalkane?
A. HBr
B. HBr, ROOR
C. Br₂, 20 °C (in inert solvent)
D. NBS
Rationale: Br₂ adds across C=C to give vicinal (1,2-) dibromide via bromonium ion.
4. Which conditions hydrogenate an alkene → alkane?
A. Na, NH₃
B. Lindlar catalyst + H₂
C. Ni or Pt catalyst with H₂ gas
D. HBr, ROOR
Rationale: H₂ with metal catalysts (Pd, Pt, Ni) performs catalytic hydrogenation (syn).
5. Which reagent set performs alkene → alcohol via acid-catalyzed hydration?
A. BH₃, H₂O₂
B. OsO₄, NMO
C. H₃PO₄ (or conc. H₂SO₄) and H₂O
D. O₃, DMS
Rationale: Strong acid + water yields Markovnikov hydration to alcohol.
, ESTUDYR
6. Conditions for alcohol → alkene (dehydration)?
A. NaBH₄
B. Conc. H₂SO₄ or Al₂O₃ at high T
C. PCC, CH₂Cl₂
D. OsO₄
Rationale: Acid-catalyzed dehydration (E1/E2 depending on substrate) eliminates water
to form alkene.
7. How to convert bromoalkane → alcohol (nucleophilic substitution)?
A. HBr
B. NaOH (aqueous / SN1 or SN2 depending on substrate)
C. LiAlH₄
D. H₂, Pd/C
Rationale: Hydroxide displaces halide to give alcohol.
8. Which oxidant converts a primary alcohol → aldehyde (stops at aldehyde)?
A. KMnO₄ (aq, hot)
B. H₂CrO₄ (strong)
C. PCC (pyridinium chlorochromate)
D. NaBH₄
Rationale: PCC in nonaqueous solvent oxidizes 1° alcohols to aldehydes without
overoxidation.
9. Which reagent oxidizes a primary alcohol → carboxylic acid?
A. PCC
B. K₂Cr₂O₇ / H₂SO₄ (strong oxidizing acidic conditions)
C. NaBH₄
D. Lindlar catalyst
Rationale: Strong chromium oxidants fully oxidize 1° alcohols to carboxylic acids.
10. Which reagent oxidizes a secondary alcohol → ketone?
A. LiAlH₄
B. NaBH₄
C. K₂Cr₂O₇ / H₂SO₄ (or PCC, CrO₃)
D. H₂, Pd/C
Rationale: Secondary alcohols are oxidized to ketones by common oxidants (chromium-
based or PCC).
11. Which statement about chromic acid (H₂CrO₄) is correct?
A. Mild, stops at aldehydes.
