Question 1
,What is the hybridization and approximate bond angle of the central carbon atom
in allene (H2 C=C=CH2 )?
• A. sp3 , 109.5∘
• B. sp2 , 120∘
• C. Central carbon is sp (180∘ ); terminal carbons are sp2 (120∘ )
• D. All carbons are sp3
Correct Answer: C
Rationale: The central carbon forms two double bonds (one to each adjacent carbon),
giving it a steric number of 2, which corresponds to sp hybridization and a linear
geometry (180∘ ). The terminal carbons each form one double bond and two single
bonds, making them sp2 hybridized (120∘ ).
Question 2
Which of the following molecules has the highest dipole moment?
• A. Carbon dioxide (CO2 )
• B. Trans-1,2-dichloroethene
• C. Cis-1,2-dichloroethene
• D. Benzene (C6 H6 )
Correct Answer: C
Rationale: Cis-1,2-dichloroethene has polar C-Cl bonds oriented in the same general
direction, resulting in vector addition and a net molecular dipole moment. In contrast,
trans-1,2-dichloroethene and CO2 are symmetrical, causing their bond dipoles to cancel
out completely (dipole moment = 0).
Module 2: Stereochemistry & Conformational
Analysis
Question 3
Which conformation of cyclohexane possesses the lowest potential energy and
highest stability?
• A. Half-chair conformation
• B. Twist-boat conformation
• C. Boat conformation
• D. Chair conformation
Correct Answer: D
,Rationale: The chair conformation is virtually free of angle strain and torsional strain
because all adjacent C-H bonds are staggered, making it the most stable and lowest-
energy conformation of cyclohexane.
Question 4
In a substituted cyclohexane ring, where is a bulky substituent (such as a tert-
butyl group) energetically preferred to reside?
• A. Axial position
• B. Equatorial position
• C. Bridging position
• D. It has equal energy in both positions
Correct Answer: B
Rationale: Bulky substituents prefer the equatorial position because it minimizes
severe steric hindrance known as 1,3-diaxial interactions, which destabilize the axial
conformation.
Module 3: Substitution & Elimination Mechanisms
(SN 1, SN 2,E1,E2)
Question 5
Which of the following alkyl halides reacts the fastest in an SN 2 solvolysis
reaction with sodium iodide in acetone?
• A. 2-bromopropane
• B. 2-bromo-2-methylpropane (tert-butyl bromide)
• C. 1-bromopropane
• D. 2-bromobutane
Correct Answer: C
Rationale: SN 2 reaction rates depend heavily on steric accessibility at the electrophilic
carbon. Primary alkyl halides (1-bromopropane) react significantly faster than
secondary or tertiary substrates due to minimal steric hindrance hindering the incoming
nucleophile.
Question 6
What is the principal role of potassium tert-butoxide (KO-t-Bu) when reacted with
a secondary alkyl halide?
, • A. Strong nucleophile favoring SN 2
• B. Bulky strong base favoring E2 elimination (Hofmann product)
• C. Mild oxidizing agent
• D. Free radical initiator
Correct Answer: B
Rationale: Potassium tert-butoxide is a sterically hindered, bulky strong base. Its large
size prevents it from acting effectively as a nucleophile in substitution; instead, it
abstracts a proton to drive an E2 elimination, favoring the less-substituted alkene
(Hofmann product).
Module 4: Alkenes, Alkynes & Addition Reactions
Question 7
What is the major organic product formed when 1-methylcyclopentene is treated
with BH3 ⋅ THF followed by alkaline hydrogen peroxide (H2 O2 /NaOH)?
• A. 2-methylcyclopentanol (Markovnikov product)
• B. 1-methylcyclopentanol (anti-Markovnikov, syn-addition product)
• C. 1-methylcyclopentene oxide
• D. Cyclopentylmethanol
Correct Answer: B
Rationale: Hydroboration-oxidation results in anti-Markovnikov hydration where the
hydroxyl group (-OH) adds to the less-substituted carbon of the double bond with overall
syn-stereochemistry.
Question 8
Which reagent combination reduces an internal alkyne specifically to a cis-
alkene?
• A. Na in liquid NH3
• B. H2 over Lindlar's catalyst
• C. Excess H2 over Pd/C
• D. Aqueous H2 SO4 and HgSO4
Correct Answer: B
Rationale: Lindlar's catalyst (poisoned palladium) facilitates catalytic hydrogenation of
alkynes with stereospecific cis-addition, yielding cis-alkenes. Conversely, dissolving
metal reduction (Na/NH3 ) yields trans-alkenes.
,What is the hybridization and approximate bond angle of the central carbon atom
in allene (H2 C=C=CH2 )?
• A. sp3 , 109.5∘
• B. sp2 , 120∘
• C. Central carbon is sp (180∘ ); terminal carbons are sp2 (120∘ )
• D. All carbons are sp3
Correct Answer: C
Rationale: The central carbon forms two double bonds (one to each adjacent carbon),
giving it a steric number of 2, which corresponds to sp hybridization and a linear
geometry (180∘ ). The terminal carbons each form one double bond and two single
bonds, making them sp2 hybridized (120∘ ).
Question 2
Which of the following molecules has the highest dipole moment?
• A. Carbon dioxide (CO2 )
• B. Trans-1,2-dichloroethene
• C. Cis-1,2-dichloroethene
• D. Benzene (C6 H6 )
Correct Answer: C
Rationale: Cis-1,2-dichloroethene has polar C-Cl bonds oriented in the same general
direction, resulting in vector addition and a net molecular dipole moment. In contrast,
trans-1,2-dichloroethene and CO2 are symmetrical, causing their bond dipoles to cancel
out completely (dipole moment = 0).
Module 2: Stereochemistry & Conformational
Analysis
Question 3
Which conformation of cyclohexane possesses the lowest potential energy and
highest stability?
• A. Half-chair conformation
• B. Twist-boat conformation
• C. Boat conformation
• D. Chair conformation
Correct Answer: D
,Rationale: The chair conformation is virtually free of angle strain and torsional strain
because all adjacent C-H bonds are staggered, making it the most stable and lowest-
energy conformation of cyclohexane.
Question 4
In a substituted cyclohexane ring, where is a bulky substituent (such as a tert-
butyl group) energetically preferred to reside?
• A. Axial position
• B. Equatorial position
• C. Bridging position
• D. It has equal energy in both positions
Correct Answer: B
Rationale: Bulky substituents prefer the equatorial position because it minimizes
severe steric hindrance known as 1,3-diaxial interactions, which destabilize the axial
conformation.
Module 3: Substitution & Elimination Mechanisms
(SN 1, SN 2,E1,E2)
Question 5
Which of the following alkyl halides reacts the fastest in an SN 2 solvolysis
reaction with sodium iodide in acetone?
• A. 2-bromopropane
• B. 2-bromo-2-methylpropane (tert-butyl bromide)
• C. 1-bromopropane
• D. 2-bromobutane
Correct Answer: C
Rationale: SN 2 reaction rates depend heavily on steric accessibility at the electrophilic
carbon. Primary alkyl halides (1-bromopropane) react significantly faster than
secondary or tertiary substrates due to minimal steric hindrance hindering the incoming
nucleophile.
Question 6
What is the principal role of potassium tert-butoxide (KO-t-Bu) when reacted with
a secondary alkyl halide?
, • A. Strong nucleophile favoring SN 2
• B. Bulky strong base favoring E2 elimination (Hofmann product)
• C. Mild oxidizing agent
• D. Free radical initiator
Correct Answer: B
Rationale: Potassium tert-butoxide is a sterically hindered, bulky strong base. Its large
size prevents it from acting effectively as a nucleophile in substitution; instead, it
abstracts a proton to drive an E2 elimination, favoring the less-substituted alkene
(Hofmann product).
Module 4: Alkenes, Alkynes & Addition Reactions
Question 7
What is the major organic product formed when 1-methylcyclopentene is treated
with BH3 ⋅ THF followed by alkaline hydrogen peroxide (H2 O2 /NaOH)?
• A. 2-methylcyclopentanol (Markovnikov product)
• B. 1-methylcyclopentanol (anti-Markovnikov, syn-addition product)
• C. 1-methylcyclopentene oxide
• D. Cyclopentylmethanol
Correct Answer: B
Rationale: Hydroboration-oxidation results in anti-Markovnikov hydration where the
hydroxyl group (-OH) adds to the less-substituted carbon of the double bond with overall
syn-stereochemistry.
Question 8
Which reagent combination reduces an internal alkyne specifically to a cis-
alkene?
• A. Na in liquid NH3
• B. H2 over Lindlar's catalyst
• C. Excess H2 over Pd/C
• D. Aqueous H2 SO4 and HgSO4
Correct Answer: B
Rationale: Lindlar's catalyst (poisoned palladium) facilitates catalytic hydrogenation of
alkynes with stereospecific cis-addition, yielding cis-alkenes. Conversely, dissolving
metal reduction (Na/NH3 ) yields trans-alkenes.
