CHEM 51B REAGENTS EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026
HBr (alkene addition) - Answers Carbocation mechanism. Markovnikov. Rearrangements possible.
Not stereospecific.
HCl (alkene addition) - Answers Carbocation. Markovnikov. Rearrangements possible.
HI (alkene addition) - Answers Carbocation. Markovnikov. Rearrangements possible. Most reactive
HX.
H₂O + H₂SO₄ (dilute) - Answers Acid-catalyzed hydration of alkene. Carbocation. Markovnikov alcohol.
Rearrangements possible.
H₂SO₄ (conc) - Answers E1 dehydration of alcohol. Carbocation intermediate. Rearrangements
possible.
HBr (ether cleavage) - Answers Protonate ether → SN1 at secondary/tertiary side. Primary side = SN2.
Br₂ - Answers Forms bromonium ion. Anti addition. Vicinal dibromide. No rearrangements.
Br₂ + CCl₄ - Answers Same as above. Inert solvent. Forms bromonium ion. Anti addition. Vicinal
dibromide. No rearrangements.
Br₂ + CH₂Cl₂ - Answers Same as above. Inert solvent.Forms bromonium ion. Anti addition. Vicinal
dibromide. No rearrangements.
Br₂ + H₂O - Answers Bromonium → water attack. Anti addition. Halohydrin. OH to more substituted
carbon.
BH₃ - Answers Syn addition. Anti-Markovnikov. No rearrangements.
THF - Answers Solvent for BH₃.
H₂O₂ - Answers Oxidative workup after hydroboration.
9-BBN - Answers Hydroboration of alkynes. Anti-Markovnikov. Terminal → aldehyde.
HgSO₄ - Answers Activates alkyne for hydration.
H₂SO₄ (with HgSO₄) - Answers Acidic environment for alkyne hydration.
H₂O (with HgSO₄) - Answers Nucleophile in alkyne hydration. Result: Markovnikov ketone. Terminal
→ methyl ketone.
PBr₃ - Answers Alcohol → alkyl bromide. SN2. Inversion.
SOCl₂ - Answers Alcohol → alkyl chloride. SN2. Inversion.
Pyridine - Answers Base used with SOCl₂ or TsCl. Neutralizes HCl.
TsCl - Answers Converts OH → OTs. Retention. Makes good leaving group.
RC≡C⁻ (acetylide) - Answers Strong nucleophile. SN2 chain extension.
CH₃Br - Answers Methyl halide. Ideal SN2 partner.
4-carbon chain Br (primary alkyl bromide) - Answers Primary electrophile for SN2 extension.
t-BuO⁻ - Answers Bulky base. E2. Hofmann product.
EtO⁻ - Answers Small base. E2. Zaitsev product.
NaOH - Answers Primary → SN2. Secondary → E2 likely. Tertiary → E2.
HO⁻ - Answers Strong base/nucleophile. E2 or SN2.
RO⁻ - Answers Alkoxide. Strong base. E2 favored.
NaNH₂ (with alkyl halide) - Answers Strong base. E2 double elimination → alkyne.
NaH - Answers Strong base only. Deprotonates alcohol → alkoxide.
NaNH₂ (terminal alkyne) - Answers Deprotonates terminal alkyne → acetylide.
Na / NH₃ (l), −78°C - Answers Radical mechanism. Anti addition. Alkyne → trans alkene.
H₂ - Answers Hydrogen gas.
Pd - Answers Catalyst for hydrogenation.
Pt - Answers Catalyst for hydrogenation.
Ni - Answers Catalyst for hydrogenation.
Lindlar's Catalyst - Answers Poisoned Pd. Syn reduction. Alkyne → cis alkene.
LiAlH₄ - Answers Strong hydride donor. Reduces carbonyls. Opens epoxides at less substituted
carbon. Needs workup.
H₃O⁺ - Answers Acidic workup. Protonates. Drives tautomerization.
Halohydrin + Base - Answers Intramolecular SN2. Forms epoxide. Inversion at attacked carbon.
CCl₄ - Answers Inert solvent for Br₂ addition.
CH₂Cl₂ - Answers Inert solvent for halogenation.
CH₃OH - Answers Weak nucleophile. Protic solvent. SN1 conditions possible.
H₂O (neutral) - Answers Weak nucleophile. Used in hydration or workup.
HBr (alkene addition) - Answers Carbocation mechanism. Markovnikov. Rearrangements possible.
Not stereospecific.
HCl (alkene addition) - Answers Carbocation. Markovnikov. Rearrangements possible.
HI (alkene addition) - Answers Carbocation. Markovnikov. Rearrangements possible. Most reactive
HX.
H₂O + H₂SO₄ (dilute) - Answers Acid-catalyzed hydration of alkene. Carbocation. Markovnikov alcohol.
Rearrangements possible.
H₂SO₄ (conc) - Answers E1 dehydration of alcohol. Carbocation intermediate. Rearrangements
possible.
HBr (ether cleavage) - Answers Protonate ether → SN1 at secondary/tertiary side. Primary side = SN2.
Br₂ - Answers Forms bromonium ion. Anti addition. Vicinal dibromide. No rearrangements.
Br₂ + CCl₄ - Answers Same as above. Inert solvent. Forms bromonium ion. Anti addition. Vicinal
dibromide. No rearrangements.
Br₂ + CH₂Cl₂ - Answers Same as above. Inert solvent.Forms bromonium ion. Anti addition. Vicinal
dibromide. No rearrangements.
Br₂ + H₂O - Answers Bromonium → water attack. Anti addition. Halohydrin. OH to more substituted
carbon.
BH₃ - Answers Syn addition. Anti-Markovnikov. No rearrangements.
THF - Answers Solvent for BH₃.
H₂O₂ - Answers Oxidative workup after hydroboration.
9-BBN - Answers Hydroboration of alkynes. Anti-Markovnikov. Terminal → aldehyde.
HgSO₄ - Answers Activates alkyne for hydration.
H₂SO₄ (with HgSO₄) - Answers Acidic environment for alkyne hydration.
H₂O (with HgSO₄) - Answers Nucleophile in alkyne hydration. Result: Markovnikov ketone. Terminal
→ methyl ketone.
PBr₃ - Answers Alcohol → alkyl bromide. SN2. Inversion.
SOCl₂ - Answers Alcohol → alkyl chloride. SN2. Inversion.
Pyridine - Answers Base used with SOCl₂ or TsCl. Neutralizes HCl.
TsCl - Answers Converts OH → OTs. Retention. Makes good leaving group.
RC≡C⁻ (acetylide) - Answers Strong nucleophile. SN2 chain extension.
CH₃Br - Answers Methyl halide. Ideal SN2 partner.
4-carbon chain Br (primary alkyl bromide) - Answers Primary electrophile for SN2 extension.
t-BuO⁻ - Answers Bulky base. E2. Hofmann product.
EtO⁻ - Answers Small base. E2. Zaitsev product.
NaOH - Answers Primary → SN2. Secondary → E2 likely. Tertiary → E2.
HO⁻ - Answers Strong base/nucleophile. E2 or SN2.
RO⁻ - Answers Alkoxide. Strong base. E2 favored.
NaNH₂ (with alkyl halide) - Answers Strong base. E2 double elimination → alkyne.
NaH - Answers Strong base only. Deprotonates alcohol → alkoxide.
NaNH₂ (terminal alkyne) - Answers Deprotonates terminal alkyne → acetylide.
Na / NH₃ (l), −78°C - Answers Radical mechanism. Anti addition. Alkyne → trans alkene.
H₂ - Answers Hydrogen gas.
Pd - Answers Catalyst for hydrogenation.
Pt - Answers Catalyst for hydrogenation.
Ni - Answers Catalyst for hydrogenation.
Lindlar's Catalyst - Answers Poisoned Pd. Syn reduction. Alkyne → cis alkene.
LiAlH₄ - Answers Strong hydride donor. Reduces carbonyls. Opens epoxides at less substituted
carbon. Needs workup.
H₃O⁺ - Answers Acidic workup. Protonates. Drives tautomerization.
Halohydrin + Base - Answers Intramolecular SN2. Forms epoxide. Inversion at attacked carbon.
CCl₄ - Answers Inert solvent for Br₂ addition.
CH₂Cl₂ - Answers Inert solvent for halogenation.
CH₃OH - Answers Weak nucleophile. Protic solvent. SN1 conditions possible.
H₂O (neutral) - Answers Weak nucleophile. Used in hydration or workup.
