CHM 2210 Exam 2 V3 | CHM 2210 Organic Chemistry I | Actual Q&A
with Rationale (CHM2210 Exam 2) | University of Central Florida
1. Which of the following statements correctly describes the relationship between (2R,3R)-
2,3-dichloropentane and (2S,3S)-2,3-dichloropentane?
A. They are enantiomers
B. They are diastereomers
C. They are meso compounds
D. They are constitutional isomers
Correct Answer: A
Explanation: Enantiomers are non-superimposable mirror images of each other. In this
case, both stereocenters have been inverted from (R,R) to (S,S), creating a mirror image
relationship. Because the molecule lacks an internal plane of symmetry, these two forms
are distinct optical isomers.
2. In an SN2 reaction, what happens to the rate of the reaction if the concentration of the
nucleophile is tripled and the concentration of the alkyl halide is doubled?
A. The rate increases by a factor of 5
B. The rate remains unchanged
C. The rate increases by a factor of 3
D. The rate increases by a factor of 6
Correct Answer: D
Explanation: The SN2 reaction follows second-order kinetics, meaning the rate law is
defined as Rate = k[substrate][nucleophile]. By tripling the nucleophile concentration and
doubling the substrate concentration, the overall rate is multiplied by 3 times 2. This
mathematical relationship highlights the bimolecular nature of the transition state in
substitution reactions.
3. Which of the following solvents is considered the best choice for promoting an SN2
reaction?
A. Dimethylsulfoxide (DMSO)
B. Methanol
C. Water
D. Ethanol
,Correct Answer: A
Explanation: Polar aprotic solvents like DMSO are preferred for SN2 reactions because
they do not solvate the nucleophile strongly. Unlike protic solvents, they lack hydrogen-
bond donating groups that would encage the nucleophile in a solvent shell. This lack of
solvation increases the nucleophile’s energy and reactivity, thereby accelerating the
reaction rate.
4. Which carbocation is the most stable among the following options?
A. A primary carbocation
B. A tertiary carbocation
C. A secondary carbocation
D. A methyl cation
Correct Answer: B
Explanation: Carbocation stability is determined by the degree of alkyl substitution, which
provides stabilization through hyperconjugation and inductive effects. Tertiary
carbocations have three alkyl groups that donate electron density to the vacant p-orbital of
the carbon. This dispersal of positive charge makes the tertiary structure the most stable
intermediate in this series.
5. Which of the following is a requirement for a successful E2 elimination reaction?
A. The formation of a carbocation intermediate
B. A polar protic solvent to stabilize the transition state
C. The presence of a weak base
D. An anti-periplanar geometry between the proton and the leaving group
Correct Answer: D
Explanation: The E2 mechanism is a concerted process that requires the overlapping of
orbitals to form a new pi bond. The leaving group and the hydrogen atom being removed
must be in an anti-periplanar alignment to allow for maximum orbital overlap in the
transition state. This stereoelectronic requirement dictates the regiochemistry and
stereochemistry of the resulting alkene.
6. Identify the major product of the E2 reaction of 2-bromo-2-methylbutane with sodium
ethoxide.
A. 2-methyl-1-butene
B. 2-methyl-2-butene
C. 2-methyl-2-butanol
D. 3-methyl-1-butene
, Correct Answer: B
Explanation: According to Zaitsev’s rule, the major product of an elimination reaction is
the most substituted alkene. Sodium ethoxide is a relatively small, strong base that will
preferentially abstract a proton from the more substituted carbon. This leads to the
formation of 2-methyl-2-butene, which is more thermodynamically stable than its isomer.
7. What is the relationship between cis-1,2-dimethylcyclohexane and trans-1,2-
dimethylcyclohexane?
A. Enantiomers
B. Diastereomers
C. Constitutional isomers
D. Identical compounds
Correct Answer: B
Explanation: Diastereomers are stereoisomers that are not mirror images of one another.
The cis and trans isomers differ in their spatial arrangement at the chiral centers but are
not related by reflection. Because they have different physical properties like boiling points
and densities, they are categorized as diastereomers.
8. Which of the following molecules contains a meso structure?
A. (2R,3R)-2,3-dibromobutane
B. (2R,3S)-2,3-dibromobutane
C. (2S,3S)-2,3-dibromobutane
D. (R)-2-bromobutane
Correct Answer: B
Explanation: A meso compound is a molecule that contains chiral centers but is achiral
overall due to an internal plane of symmetry. In the (2R,3S) configuration of 2,3-
dibromobutane, the top half of the molecule is the mirror image of the bottom half. This
symmetry results in the cancellation of optical activity, rendering the molecule achiral.
9. Which of the following is the best leaving group in a nucleophilic substitution reaction?
A. F-
B. OH-
C. I-
D. NH2-
Correct Answer: C
with Rationale (CHM2210 Exam 2) | University of Central Florida
1. Which of the following statements correctly describes the relationship between (2R,3R)-
2,3-dichloropentane and (2S,3S)-2,3-dichloropentane?
A. They are enantiomers
B. They are diastereomers
C. They are meso compounds
D. They are constitutional isomers
Correct Answer: A
Explanation: Enantiomers are non-superimposable mirror images of each other. In this
case, both stereocenters have been inverted from (R,R) to (S,S), creating a mirror image
relationship. Because the molecule lacks an internal plane of symmetry, these two forms
are distinct optical isomers.
2. In an SN2 reaction, what happens to the rate of the reaction if the concentration of the
nucleophile is tripled and the concentration of the alkyl halide is doubled?
A. The rate increases by a factor of 5
B. The rate remains unchanged
C. The rate increases by a factor of 3
D. The rate increases by a factor of 6
Correct Answer: D
Explanation: The SN2 reaction follows second-order kinetics, meaning the rate law is
defined as Rate = k[substrate][nucleophile]. By tripling the nucleophile concentration and
doubling the substrate concentration, the overall rate is multiplied by 3 times 2. This
mathematical relationship highlights the bimolecular nature of the transition state in
substitution reactions.
3. Which of the following solvents is considered the best choice for promoting an SN2
reaction?
A. Dimethylsulfoxide (DMSO)
B. Methanol
C. Water
D. Ethanol
,Correct Answer: A
Explanation: Polar aprotic solvents like DMSO are preferred for SN2 reactions because
they do not solvate the nucleophile strongly. Unlike protic solvents, they lack hydrogen-
bond donating groups that would encage the nucleophile in a solvent shell. This lack of
solvation increases the nucleophile’s energy and reactivity, thereby accelerating the
reaction rate.
4. Which carbocation is the most stable among the following options?
A. A primary carbocation
B. A tertiary carbocation
C. A secondary carbocation
D. A methyl cation
Correct Answer: B
Explanation: Carbocation stability is determined by the degree of alkyl substitution, which
provides stabilization through hyperconjugation and inductive effects. Tertiary
carbocations have three alkyl groups that donate electron density to the vacant p-orbital of
the carbon. This dispersal of positive charge makes the tertiary structure the most stable
intermediate in this series.
5. Which of the following is a requirement for a successful E2 elimination reaction?
A. The formation of a carbocation intermediate
B. A polar protic solvent to stabilize the transition state
C. The presence of a weak base
D. An anti-periplanar geometry between the proton and the leaving group
Correct Answer: D
Explanation: The E2 mechanism is a concerted process that requires the overlapping of
orbitals to form a new pi bond. The leaving group and the hydrogen atom being removed
must be in an anti-periplanar alignment to allow for maximum orbital overlap in the
transition state. This stereoelectronic requirement dictates the regiochemistry and
stereochemistry of the resulting alkene.
6. Identify the major product of the E2 reaction of 2-bromo-2-methylbutane with sodium
ethoxide.
A. 2-methyl-1-butene
B. 2-methyl-2-butene
C. 2-methyl-2-butanol
D. 3-methyl-1-butene
, Correct Answer: B
Explanation: According to Zaitsev’s rule, the major product of an elimination reaction is
the most substituted alkene. Sodium ethoxide is a relatively small, strong base that will
preferentially abstract a proton from the more substituted carbon. This leads to the
formation of 2-methyl-2-butene, which is more thermodynamically stable than its isomer.
7. What is the relationship between cis-1,2-dimethylcyclohexane and trans-1,2-
dimethylcyclohexane?
A. Enantiomers
B. Diastereomers
C. Constitutional isomers
D. Identical compounds
Correct Answer: B
Explanation: Diastereomers are stereoisomers that are not mirror images of one another.
The cis and trans isomers differ in their spatial arrangement at the chiral centers but are
not related by reflection. Because they have different physical properties like boiling points
and densities, they are categorized as diastereomers.
8. Which of the following molecules contains a meso structure?
A. (2R,3R)-2,3-dibromobutane
B. (2R,3S)-2,3-dibromobutane
C. (2S,3S)-2,3-dibromobutane
D. (R)-2-bromobutane
Correct Answer: B
Explanation: A meso compound is a molecule that contains chiral centers but is achiral
overall due to an internal plane of symmetry. In the (2R,3S) configuration of 2,3-
dibromobutane, the top half of the molecule is the mirror image of the bottom half. This
symmetry results in the cancellation of optical activity, rendering the molecule achiral.
9. Which of the following is the best leaving group in a nucleophilic substitution reaction?
A. F-
B. OH-
C. I-
D. NH2-
Correct Answer: C
