Organic Chemistry Comprehensive Practice Exam & Test
Bank | Fundamental Mechanisms, Reaction Kinetics,
Stereochemistry, and Synthesis Practice Questions with
Verified Answers and Solutions
1. Which of the following carbocations is the most stable?
A. Ethyl cation
B. tert-Butyl cation
C. Methyl cation
D. Isopropyl cation
Rationale: Carbocation stability increases with substitution due to hyperconjugation and
inductive donation from alkyl groups. Tertiary carbocations (like tert-butyl) are more stable
than secondary, primary, and methyl carbocations.
2. What is the major product formed when 2-bromobutane undergoes an E2 reaction with
sodium ethoxide in ethanol?
A. 1-Butene
B. (E)-2-Butene
C. 1-Butanol
D. 2-Butanol
Rationale: E2 elimination with a non-bulky base like ethoxide follows Zaitsev's rule, favoring
the more substituted alkene. (E)-2-Butene is the major product due to higher thermodynamic
stability compared to the Z-isomer and 1-butene.
3. Which functional group exhibits a sharp, strong infrared (IR) absorption peak near
1715 cm⁻¹?
A. Alcohol (-OH)
B. Alkyne (C≡C)
C. Carbonyl (C=O)
D. Amine (-NH2)
Rationale: Carbonyl compounds (ketones, aldehydes, carboxylic acids) typically exhibit a
strong, distinct absorption peak in the 1680–1750 cm⁻¹ region due to C=O stretching
vibrations.
4. An SN2 reaction at a chiral center proceeds with which stereochemical outcome?
A. Inversion of configuration
B. Retention of configuration
C. Racemization
D. Formation of diastereomers only
, Rationale: SN2 reactions involve a backside attack by the nucleophile on the electrophilic
carbon, resulting in a complete inversion of stereochemical configuration (Walden inversion).
5. Which reagent is best suited for converting a primary alcohol directly into an aldehyde
without over-oxidizing to a carboxylic acid?
A. Chromic acid (H2CrO4)
B. Pyridinium chlorochromate (PCC)
C. Potassium permanganate (KMnO4)
D. Sodium dichromate (Na2Cr2O7)
Rationale: PCC is a mild oxidizing agent that selectively oxidizes primary alcohols to
aldehydes. Strong oxidizers like H2CrO4, KMnO4, or Na2Cr2O7 in aqueous media oxidize
primary alcohols all the way to carboxylic acids.
6. What is the hybridization of the central carbon in propadiene (allene, H2C=C=CH2)?
A. sp3
B. sp
C. sp2
D. dsp2
Rationale: The central carbon forms two double bonds (two sigma bonds and two pi bonds)
at 180° angles, requiring sp hybridization.
7. Which of the following compounds is aromatic according to Hückel's Rule?
A. Cyclooctatetraene
B. Cyclopentadienyl cation
C. Cyclopentadienyl anion
D. 1,3-Cyclohexadiene
Rationale: To be aromatic, a compound must be cyclic, planar, fully conjugated, and have
(4n + 2) pi electrons. The cyclopentadienyl anion has 6 pi electrons (n = 1), making it
aromatic.
8. What major product is formed from the reaction of propene with HBr in the presence of
peroxides (ROOR)?
A. 2-Bromopropane
B. 1-Bromopropane
C. 1,2-Dibromopropane
D. 2,2-Dibromopropane
Rationale: In the presence of peroxides, HBr undergoes anti-Markovnikov addition via a free-
radical mechanism, adding the bromine atom to the less substituted carbon atom.
9. Which of the following nucleophiles is the strongest in a polar aprotic solvent such as
acetone?
A. Fluoride ion (F-)
Bank | Fundamental Mechanisms, Reaction Kinetics,
Stereochemistry, and Synthesis Practice Questions with
Verified Answers and Solutions
1. Which of the following carbocations is the most stable?
A. Ethyl cation
B. tert-Butyl cation
C. Methyl cation
D. Isopropyl cation
Rationale: Carbocation stability increases with substitution due to hyperconjugation and
inductive donation from alkyl groups. Tertiary carbocations (like tert-butyl) are more stable
than secondary, primary, and methyl carbocations.
2. What is the major product formed when 2-bromobutane undergoes an E2 reaction with
sodium ethoxide in ethanol?
A. 1-Butene
B. (E)-2-Butene
C. 1-Butanol
D. 2-Butanol
Rationale: E2 elimination with a non-bulky base like ethoxide follows Zaitsev's rule, favoring
the more substituted alkene. (E)-2-Butene is the major product due to higher thermodynamic
stability compared to the Z-isomer and 1-butene.
3. Which functional group exhibits a sharp, strong infrared (IR) absorption peak near
1715 cm⁻¹?
A. Alcohol (-OH)
B. Alkyne (C≡C)
C. Carbonyl (C=O)
D. Amine (-NH2)
Rationale: Carbonyl compounds (ketones, aldehydes, carboxylic acids) typically exhibit a
strong, distinct absorption peak in the 1680–1750 cm⁻¹ region due to C=O stretching
vibrations.
4. An SN2 reaction at a chiral center proceeds with which stereochemical outcome?
A. Inversion of configuration
B. Retention of configuration
C. Racemization
D. Formation of diastereomers only
, Rationale: SN2 reactions involve a backside attack by the nucleophile on the electrophilic
carbon, resulting in a complete inversion of stereochemical configuration (Walden inversion).
5. Which reagent is best suited for converting a primary alcohol directly into an aldehyde
without over-oxidizing to a carboxylic acid?
A. Chromic acid (H2CrO4)
B. Pyridinium chlorochromate (PCC)
C. Potassium permanganate (KMnO4)
D. Sodium dichromate (Na2Cr2O7)
Rationale: PCC is a mild oxidizing agent that selectively oxidizes primary alcohols to
aldehydes. Strong oxidizers like H2CrO4, KMnO4, or Na2Cr2O7 in aqueous media oxidize
primary alcohols all the way to carboxylic acids.
6. What is the hybridization of the central carbon in propadiene (allene, H2C=C=CH2)?
A. sp3
B. sp
C. sp2
D. dsp2
Rationale: The central carbon forms two double bonds (two sigma bonds and two pi bonds)
at 180° angles, requiring sp hybridization.
7. Which of the following compounds is aromatic according to Hückel's Rule?
A. Cyclooctatetraene
B. Cyclopentadienyl cation
C. Cyclopentadienyl anion
D. 1,3-Cyclohexadiene
Rationale: To be aromatic, a compound must be cyclic, planar, fully conjugated, and have
(4n + 2) pi electrons. The cyclopentadienyl anion has 6 pi electrons (n = 1), making it
aromatic.
8. What major product is formed from the reaction of propene with HBr in the presence of
peroxides (ROOR)?
A. 2-Bromopropane
B. 1-Bromopropane
C. 1,2-Dibromopropane
D. 2,2-Dibromopropane
Rationale: In the presence of peroxides, HBr undergoes anti-Markovnikov addition via a free-
radical mechanism, adding the bromine atom to the less substituted carbon atom.
9. Which of the following nucleophiles is the strongest in a polar aprotic solvent such as
acetone?
A. Fluoride ion (F-)
