CHEMISTRY 219 ORGANIC CHEMISTRY MODULE 3 : ALL
VERSIONS EXAM-PORTAGE LEARNING] – QUESTION AND
ANSWERS | VERIFIED AND WELL DETAILED ANSWERS PLUS
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1. What is the correct IUPAC name for the straight-chain alkene with five carbon atoms
and a double bond starting at the second carbon?
A. 1-pentene
B. 2-pentene
C. 2-methyl-1-butene
D. 3-pentene
The parent chain contains five carbons, designating it as a pentene. Numbering begins from
the end closest to the double bond to give it the lowest possible locant, which places the double
bond at carbon 2.
2. Which of the following describes the hybridization of the carbon atoms involved in a
carbon-carbon double bond in an alkene?
A. sp
B. sp2
C. sp3
D. p
Carbon atoms sharing a double bond are bonded to three other atoms in a trigonal planar
geometry, which corresponds to sp2 hybridization with one unhybridized p orbital remaining
to form the pi bond.
3. Which of the following compounds exhibits geometric (cis-trans) isomerism?
A. 2-methyl-2-butene
B. 1-butene
C. 2-butene
,D. 2-methyl-1-propene
Cis-trans isomerism requires each carbon of the double bond to be attached to two different
groups. 2-butene meets this requirement since each double-bond carbon is bonded to a
hydrogen and a methyl group.
4. What is the primary product formed when 2-methylpropene reacts with hydrogen
chloride (HCl)?
A. 1-chloro-2-methylpropane
B. 2-chloro-2-methylpropane
C. 2-chlorobutane
D. 1-chlorobutane
The reaction proceeds via Markovnikov's rule where the electrophilic hydrogen adds to form
the more stable tertiary carbocation intermediate, which is then attacked by the chloride ion to
yield 2-chloro-2-methylpropane.
5. Which intermediate is formed during the electrophilic addition of HBr to an alkene?
A. Carbanion
B. Free radical
C. Carbocation
D. Carbene
Electrophilic addition reactions of alkenes typically proceed through a positively charged
carbocation intermediate formed when the pi electrons attack an electrophile.
6. In the acid-catalyzed hydration of an alkene to form an alcohol, what is the role of the
acid catalyst (such as dilute sulfuric acid)?
A. To act as a nucleophile
B. To protonate the alkene and form a carbocation intermediate
C. To reduce the double bond
D. To oxidize the carbon chain
, The acid catalyst donates a proton to the alkene pi bond, generating a high-energy
carbocation intermediate that is subsequently attacked by water.
7. What is the stereochemical outcome of the halogenation of an alkene (e.g., addition of
Br2 to trans-2-butene)?
A. Syn addition yielding a meso compound
B. Anti addition yielding a racemic mixture
C. Syn addition yielding a racemic mixture
D. Anti addition yielding a meso compound
Halogenation of alkenes proceeds via a cyclic bromonium ion intermediate, leading strictly to
anti addition. Adding Br2 to trans-2-butene via anti addition results in the formation of a
meso stereoisomer.
8. Which reagent is used to convert an alkene into a 1,2-diol via a syn-addition pathway?
A. Br2 in CCl4
B. Cold, dilute KMnO4
C. Concentrated H2SO4 and heat
D. H2 and Pd/C
Cold, dilute potassium permanganate (or OsO4) reacts with alkenes to deliver two hydroxyl
groups to the same face of the double bond, achieving syn-dihydroxylation.
9. Which of the following reactions results in anti-Markovnikov addition of water across a
double bond?
A. Acid-catalyzed hydration
B. Oxymercuration-demercuration
C. Hydroboration-oxidation
D. Catalytic hydrogenation
Hydroboration-oxidation employs BH3 followed by H2O2/NaOH to achieve syn addition of
water with anti-Markovnikov regioselectivity, placing the hydroxyl group on the less
substituted carbon.
VERSIONS EXAM-PORTAGE LEARNING] – QUESTION AND
ANSWERS | VERIFIED AND WELL DETAILED ANSWERS PLUS
RATIONALES | GUARANTEED PASS | LATEST EXAM UPDATE |
EXAM PREP | STUDY GUIDE | PRACTICE TEST
1. What is the correct IUPAC name for the straight-chain alkene with five carbon atoms
and a double bond starting at the second carbon?
A. 1-pentene
B. 2-pentene
C. 2-methyl-1-butene
D. 3-pentene
The parent chain contains five carbons, designating it as a pentene. Numbering begins from
the end closest to the double bond to give it the lowest possible locant, which places the double
bond at carbon 2.
2. Which of the following describes the hybridization of the carbon atoms involved in a
carbon-carbon double bond in an alkene?
A. sp
B. sp2
C. sp3
D. p
Carbon atoms sharing a double bond are bonded to three other atoms in a trigonal planar
geometry, which corresponds to sp2 hybridization with one unhybridized p orbital remaining
to form the pi bond.
3. Which of the following compounds exhibits geometric (cis-trans) isomerism?
A. 2-methyl-2-butene
B. 1-butene
C. 2-butene
,D. 2-methyl-1-propene
Cis-trans isomerism requires each carbon of the double bond to be attached to two different
groups. 2-butene meets this requirement since each double-bond carbon is bonded to a
hydrogen and a methyl group.
4. What is the primary product formed when 2-methylpropene reacts with hydrogen
chloride (HCl)?
A. 1-chloro-2-methylpropane
B. 2-chloro-2-methylpropane
C. 2-chlorobutane
D. 1-chlorobutane
The reaction proceeds via Markovnikov's rule where the electrophilic hydrogen adds to form
the more stable tertiary carbocation intermediate, which is then attacked by the chloride ion to
yield 2-chloro-2-methylpropane.
5. Which intermediate is formed during the electrophilic addition of HBr to an alkene?
A. Carbanion
B. Free radical
C. Carbocation
D. Carbene
Electrophilic addition reactions of alkenes typically proceed through a positively charged
carbocation intermediate formed when the pi electrons attack an electrophile.
6. In the acid-catalyzed hydration of an alkene to form an alcohol, what is the role of the
acid catalyst (such as dilute sulfuric acid)?
A. To act as a nucleophile
B. To protonate the alkene and form a carbocation intermediate
C. To reduce the double bond
D. To oxidize the carbon chain
, The acid catalyst donates a proton to the alkene pi bond, generating a high-energy
carbocation intermediate that is subsequently attacked by water.
7. What is the stereochemical outcome of the halogenation of an alkene (e.g., addition of
Br2 to trans-2-butene)?
A. Syn addition yielding a meso compound
B. Anti addition yielding a racemic mixture
C. Syn addition yielding a racemic mixture
D. Anti addition yielding a meso compound
Halogenation of alkenes proceeds via a cyclic bromonium ion intermediate, leading strictly to
anti addition. Adding Br2 to trans-2-butene via anti addition results in the formation of a
meso stereoisomer.
8. Which reagent is used to convert an alkene into a 1,2-diol via a syn-addition pathway?
A. Br2 in CCl4
B. Cold, dilute KMnO4
C. Concentrated H2SO4 and heat
D. H2 and Pd/C
Cold, dilute potassium permanganate (or OsO4) reacts with alkenes to deliver two hydroxyl
groups to the same face of the double bond, achieving syn-dihydroxylation.
9. Which of the following reactions results in anti-Markovnikov addition of water across a
double bond?
A. Acid-catalyzed hydration
B. Oxymercuration-demercuration
C. Hydroboration-oxidation
D. Catalytic hydrogenation
Hydroboration-oxidation employs BH3 followed by H2O2/NaOH to achieve syn addition of
water with anti-Markovnikov regioselectivity, placing the hydroxyl group on the less
substituted carbon.
