CHM 2210 Exam 2 V1 | CHM 2210 Organic Chemistry I | Actual Q&A
with Rationale (CHM2210 Exam 2) | University of Central Florida
1. In a Newman projection of butane looking down the C2-C3 bond, which conformation
represents the global energy minimum?
A. Gauche
B. Total eclipsed
C. Eclipsed
D. Anti-staggered
Correct Answer: D
Explanation: The anti-staggered conformation minimizes steric hindrance between the
two bulky methyl groups by placing them 180 degrees apart. This orientation results in the
lowest potential energy for the molecule compared to other staggered or eclipsed forms.
Gauche conformations are also staggered but suffer from unfavorable steric interactions
between adjacent methyl groups.
2. Which of the following is the defining characteristic of a meso compound?
A. It is a mixture of equal amounts of two enantiomers.
B. It has no stereocenters and is therefore achiral.
C. It rotates plane-polarized light in a clockwise direction.
D. It contains stereocenters but is achiral due to an internal plane of symmetry.
Correct Answer: D
Explanation: Meso compounds are unique because they possess multiple stereocenters
while remaining optically inactive. This lack of chirality is due to an internal plane of
symmetry that makes the molecule superimposable on its mirror image. Consequently,
meso compounds do not rotate plane-polarized light despite having chiral carbons.
3. When comparing (2R, 3R)-dibromobutane and (2S, 3S)-dibromobutane, what is their
stereoisomeric relationship?
A. Diastereomers
B. Constitutional isomers
C. Identical compounds
D. Enantiomers
Correct Answer: D
,Explanation: Enantiomers are non-superimposable mirror images of one another that
have opposite configurations at every stereocenter. In this case, both the 2R and 3R centers
are inverted to 2S and 3S, fulfilling the requirement for enantiomerism. These molecules
share identical physical properties such as boiling point and melting point but differ in
their interaction with chiral environments.
4. Which cycloalkane possesses the highest amount of ring strain per methylene group?
A. Cyclopropane
B. Cyclopentane
C. Cyclohexane
D. Cyclobutane
Correct Answer: A
Explanation: Cyclopropane suffers from extreme angle strain because its bond angles are
forced to be 60 degrees, which is significantly smaller than the ideal 109.5 degree
tetrahedral angle. Additionally, all C-H bonds are eclipsed, leading to significant torsional
strain. This combination of factors makes it the most strained and least stable of the
common cycloalkanes.
5. In the Cahn-Ingold-Prelog priority system, which of the following groups has the highest
priority?
A. * -OH *
B. -CHO
C. -CH2OH
D. -CH3
Correct Answer: A
Explanation: Priority is assigned based on the atomic number of the atoms directly
attached to the stereocenter. The oxygen atom in the hydroxyl group has a higher atomic
number (8) than the carbon atoms in the other three groups. Therefore, the -OH group
receives the highest priority regardless of the atoms further down the chain.
6. Which statement correctly describes the stability of substituted cyclohexane chairs?
A. Equatorial substituents are more stable because they avoid 1,3-diaxial interactions.
B. Axial substituents are more stable due to lack of steric strain.
C. Substituent position does not affect the energy of the chair.
D. Both axial and equatorial positions are energetically equivalent.
Correct Answer: A
, Explanation: Substituents in the axial position experience unfavorable steric interactions
with other axial hydrogens on the same side of the ring, known as 1,3-diaxial interactions.
Placing a substituent in the equatorial position directs it away from the ring bulk,
significantly lowering the potential energy. A larger substituent will have a stronger
preference for the equatorial position to minimize this strain.
7. For a molecule with 3 stereocenters, what is the maximum possible number of
stereoisomers?
A. 8
B. 6
C. 3
D. 9
Correct Answer: A
Explanation: The maximum number of stereoisomers for a molecule is calculated using
the formula 2^n, where n is the number of stereocenters. For a molecule with 3
stereocenters, the calculation is 2^3, which equals 8. However, the actual number may be
fewer if meso compounds are possible due to symmetry.
8. What is the relationship between (2R, 3S)-2,3-pentanediol and (2R, 3R)-2,3-pentanediol?
A. Enantiomers
B. Diastereomers
C. Identical
D. Constitutional isomers
Correct Answer: B
Explanation: Diastereomers are stereoisomers that are not mirror images of each other,
occurring when at least one but not all stereocenters are inverted. Here, the configuration
at C2 remains R in both molecules, while C3 changes from S to R. Because they are not
mirror images and not identical, they are classified as diastereomers.
9. Which of the following describes a racemic mixture?
A. A pure sample of a single enantiomer.
B. A mixture of diastereomers that can be separated by distillation.
C. An equimolar mixture of two enantiomers with an optical rotation of zero.
D. A compound with a plane of symmetry.
Correct Answer: C
with Rationale (CHM2210 Exam 2) | University of Central Florida
1. In a Newman projection of butane looking down the C2-C3 bond, which conformation
represents the global energy minimum?
A. Gauche
B. Total eclipsed
C. Eclipsed
D. Anti-staggered
Correct Answer: D
Explanation: The anti-staggered conformation minimizes steric hindrance between the
two bulky methyl groups by placing them 180 degrees apart. This orientation results in the
lowest potential energy for the molecule compared to other staggered or eclipsed forms.
Gauche conformations are also staggered but suffer from unfavorable steric interactions
between adjacent methyl groups.
2. Which of the following is the defining characteristic of a meso compound?
A. It is a mixture of equal amounts of two enantiomers.
B. It has no stereocenters and is therefore achiral.
C. It rotates plane-polarized light in a clockwise direction.
D. It contains stereocenters but is achiral due to an internal plane of symmetry.
Correct Answer: D
Explanation: Meso compounds are unique because they possess multiple stereocenters
while remaining optically inactive. This lack of chirality is due to an internal plane of
symmetry that makes the molecule superimposable on its mirror image. Consequently,
meso compounds do not rotate plane-polarized light despite having chiral carbons.
3. When comparing (2R, 3R)-dibromobutane and (2S, 3S)-dibromobutane, what is their
stereoisomeric relationship?
A. Diastereomers
B. Constitutional isomers
C. Identical compounds
D. Enantiomers
Correct Answer: D
,Explanation: Enantiomers are non-superimposable mirror images of one another that
have opposite configurations at every stereocenter. In this case, both the 2R and 3R centers
are inverted to 2S and 3S, fulfilling the requirement for enantiomerism. These molecules
share identical physical properties such as boiling point and melting point but differ in
their interaction with chiral environments.
4. Which cycloalkane possesses the highest amount of ring strain per methylene group?
A. Cyclopropane
B. Cyclopentane
C. Cyclohexane
D. Cyclobutane
Correct Answer: A
Explanation: Cyclopropane suffers from extreme angle strain because its bond angles are
forced to be 60 degrees, which is significantly smaller than the ideal 109.5 degree
tetrahedral angle. Additionally, all C-H bonds are eclipsed, leading to significant torsional
strain. This combination of factors makes it the most strained and least stable of the
common cycloalkanes.
5. In the Cahn-Ingold-Prelog priority system, which of the following groups has the highest
priority?
A. * -OH *
B. -CHO
C. -CH2OH
D. -CH3
Correct Answer: A
Explanation: Priority is assigned based on the atomic number of the atoms directly
attached to the stereocenter. The oxygen atom in the hydroxyl group has a higher atomic
number (8) than the carbon atoms in the other three groups. Therefore, the -OH group
receives the highest priority regardless of the atoms further down the chain.
6. Which statement correctly describes the stability of substituted cyclohexane chairs?
A. Equatorial substituents are more stable because they avoid 1,3-diaxial interactions.
B. Axial substituents are more stable due to lack of steric strain.
C. Substituent position does not affect the energy of the chair.
D. Both axial and equatorial positions are energetically equivalent.
Correct Answer: A
, Explanation: Substituents in the axial position experience unfavorable steric interactions
with other axial hydrogens on the same side of the ring, known as 1,3-diaxial interactions.
Placing a substituent in the equatorial position directs it away from the ring bulk,
significantly lowering the potential energy. A larger substituent will have a stronger
preference for the equatorial position to minimize this strain.
7. For a molecule with 3 stereocenters, what is the maximum possible number of
stereoisomers?
A. 8
B. 6
C. 3
D. 9
Correct Answer: A
Explanation: The maximum number of stereoisomers for a molecule is calculated using
the formula 2^n, where n is the number of stereocenters. For a molecule with 3
stereocenters, the calculation is 2^3, which equals 8. However, the actual number may be
fewer if meso compounds are possible due to symmetry.
8. What is the relationship between (2R, 3S)-2,3-pentanediol and (2R, 3R)-2,3-pentanediol?
A. Enantiomers
B. Diastereomers
C. Identical
D. Constitutional isomers
Correct Answer: B
Explanation: Diastereomers are stereoisomers that are not mirror images of each other,
occurring when at least one but not all stereocenters are inverted. Here, the configuration
at C2 remains R in both molecules, while C3 changes from S to R. Because they are not
mirror images and not identical, they are classified as diastereomers.
9. Which of the following describes a racemic mixture?
A. A pure sample of a single enantiomer.
B. A mixture of diastereomers that can be separated by distillation.
C. An equimolar mixture of two enantiomers with an optical rotation of zero.
D. A compound with a plane of symmetry.
Correct Answer: C
