CHEM 219 MODULE 5:
STEREOCHEMISTRY ADVANCED
ASSESSMENT QUESTIONS WITH
CORRECT ANSWERS 2026/2027 UPDATE.
JUST RELEASED
1. Which of the following is the correct definition of a chiral molecule?
A. A molecule that is not superimposable on its mirror image.
B. A molecule that possesses a plane of symmetry.
C. A molecule that contains at least one carbon atom with four different groups.
D. A molecule that rotates plane-polarized light in a clockwise direction.
Answer: A
Conceptual Explanation: Chirality is defined by the lack of superimposability on a mirror
image. While many chiral molecules have stereocenters, the fundamental definition is the
non-superimposable mirror image property.
2. According to Cahn-Ingold-Prelog rules, which group has the highest priority?
A. -CH2OH
B. -COOH
C. -CHO
,D. -CH2NH2
Answer: B
Conceptual Explanation: Priority is based on atomic number. Comparing the first atoms
(all C), we look at the atoms attached. -COOH has (O, O, O) due to the double bond, -CHO has
(O, O, H), -CH2OH has (O, H, H), and -CH2NH2 has (N, H, H). -COOH ranks highest.
3. What is the relationship between (2R, 3R)-2,3-dichlorobutane and (2S, 3S)-2,3-
dichlorobutane?
A. Diastereomers
B. Enantiomers
C. Constitutional isomers
D. Identical meso compounds
Answer: B
Conceptual Explanation: Since both stereocenters are inverted (R,R to S,S) and there is no
internal plane of symmetry for these specific configurations, they are non-superimposable
mirror images, or enantiomers.
4. A solution of a pure chiral compound (0.5 g in 10 mL of solvent) in a 1 dm tube gives an
observed rotation of +2.0°. What is the specific rotation [α]?
A. +4.0°
B. +10.0°
, C. +20.0°
D. +40.0°
Answer: D
Conceptual Explanation: Specific rotation = observed rotation / (concentration in g/mL *
path length in dm). Concentration = 0.5g/10mL = 0.05 g/mL. [α] = 2.0 / (0.05 * 1) = +40.0°.
5. Which molecule contains a meso isomer?
A. 2,4-dibromopentane
B. 2,3-dibromopentane
C. 2-bromo-3-chlorobutane
D. 1,2-dichloropropane
Answer: A
Conceptual Explanation: A meso compound must have two or more stereocenters and an
internal plane of symmetry. 2,4-dibromopentane (specifically the 2R, 4S isomer) has a
plane of symmetry passing through C3.
6. How many stereoisomers are possible for 2,3,4-trichloropentane?
A. 8
B. 6
C. 3
STEREOCHEMISTRY ADVANCED
ASSESSMENT QUESTIONS WITH
CORRECT ANSWERS 2026/2027 UPDATE.
JUST RELEASED
1. Which of the following is the correct definition of a chiral molecule?
A. A molecule that is not superimposable on its mirror image.
B. A molecule that possesses a plane of symmetry.
C. A molecule that contains at least one carbon atom with four different groups.
D. A molecule that rotates plane-polarized light in a clockwise direction.
Answer: A
Conceptual Explanation: Chirality is defined by the lack of superimposability on a mirror
image. While many chiral molecules have stereocenters, the fundamental definition is the
non-superimposable mirror image property.
2. According to Cahn-Ingold-Prelog rules, which group has the highest priority?
A. -CH2OH
B. -COOH
C. -CHO
,D. -CH2NH2
Answer: B
Conceptual Explanation: Priority is based on atomic number. Comparing the first atoms
(all C), we look at the atoms attached. -COOH has (O, O, O) due to the double bond, -CHO has
(O, O, H), -CH2OH has (O, H, H), and -CH2NH2 has (N, H, H). -COOH ranks highest.
3. What is the relationship between (2R, 3R)-2,3-dichlorobutane and (2S, 3S)-2,3-
dichlorobutane?
A. Diastereomers
B. Enantiomers
C. Constitutional isomers
D. Identical meso compounds
Answer: B
Conceptual Explanation: Since both stereocenters are inverted (R,R to S,S) and there is no
internal plane of symmetry for these specific configurations, they are non-superimposable
mirror images, or enantiomers.
4. A solution of a pure chiral compound (0.5 g in 10 mL of solvent) in a 1 dm tube gives an
observed rotation of +2.0°. What is the specific rotation [α]?
A. +4.0°
B. +10.0°
, C. +20.0°
D. +40.0°
Answer: D
Conceptual Explanation: Specific rotation = observed rotation / (concentration in g/mL *
path length in dm). Concentration = 0.5g/10mL = 0.05 g/mL. [α] = 2.0 / (0.05 * 1) = +40.0°.
5. Which molecule contains a meso isomer?
A. 2,4-dibromopentane
B. 2,3-dibromopentane
C. 2-bromo-3-chlorobutane
D. 1,2-dichloropropane
Answer: A
Conceptual Explanation: A meso compound must have two or more stereocenters and an
internal plane of symmetry. 2,4-dibromopentane (specifically the 2R, 4S isomer) has a
plane of symmetry passing through C3.
6. How many stereoisomers are possible for 2,3,4-trichloropentane?
A. 8
B. 6
C. 3
