CHEM 219 MODULE 4:
STEREOCHEMISTRY MASTERY TEST
QUESTIONS WITH CORRECT ANSWERS
2026/2027 UPDATE. JUST RELEASED
1. Which of the following conditions is strictly required for a molecule to be considered
‘chiral’?
A. It must contain at least one carbon atom with four different substituents.
B. It must not possess an internal plane of symmetry or a center of inversion.
C. It must rotate plane-polarized light in a clockwise direction.
D. It must have at least two stereocenters.
Answer: B
Conceptual Explanation: Chirality is defined by the absence of an improper axis of
rotation (which includes planes of symmetry and centers of inversion). While many chiral
molecules have stereocenters, some do not (like allenes), and some molecules with
stereocenters are achiral (meso compounds).
2. Using the Cahn-Ingold-Prelog (CIP) priority rules, which group has the highest priority?
A. -CH2OH
B. -COOH
,C. -CHO
D. -CH2NH2
Answer: B
Conceptual Explanation: Priority is determined by atomic number. -COOH (Carbon
double bonded to O and single bonded to O) ranks higher than -CHO (Carbon double
bonded to O and single bonded to H). -CH2NH2 and -CH2OH rank lower because the first
point of difference involves single bonds to N or O.
3. A solution contains a mixture of two enantiomers with an enantiomeric excess (ee) of 60%
of the (R)-isomer. What is the percentage of the (S)-isomer in the mixture?
A. 40%
B. 60%
C. 30%
D. 20%
Answer: D
Conceptual Explanation: If ee is 60%, then 60% is ‘excess’ R and 40% is the racemic
mixture (equal parts R and S). Therefore, the amount of S is half of the racemic portion:
40% / 2 = 20%.
4. Which statement regarding meso compounds is TRUE?
A. They are optically active due to internal compensation.
, B. They are a type of enantiomer.
C. They must contain at least two stereocenters and a plane of symmetry.
D. They have a non-superimposable mirror image.
Answer: C
Conceptual Explanation: Meso compounds contain stereocenters but are achiral overall
because they possess an internal plane of symmetry or center of inversion, making them
superimposable on their mirror image.
5. How many stereoisomers are possible for 2,3-dibromobutane?
A. 2
B. 3
C. 4
D. 8
Answer: B
Conceptual Explanation: The formula 2^n predicts 4 isomers (n=2 stereocenters), but
because the molecule is symmetrical, one pair of enantiomers is replaced by a single meso
compound. The isomers are (2R,3R), (2S,3S), and the meso (2R,3S) form.
6. Which physical property differs between a pair of pure enantiomers under non-chiral
conditions?
A. Boiling point
STEREOCHEMISTRY MASTERY TEST
QUESTIONS WITH CORRECT ANSWERS
2026/2027 UPDATE. JUST RELEASED
1. Which of the following conditions is strictly required for a molecule to be considered
‘chiral’?
A. It must contain at least one carbon atom with four different substituents.
B. It must not possess an internal plane of symmetry or a center of inversion.
C. It must rotate plane-polarized light in a clockwise direction.
D. It must have at least two stereocenters.
Answer: B
Conceptual Explanation: Chirality is defined by the absence of an improper axis of
rotation (which includes planes of symmetry and centers of inversion). While many chiral
molecules have stereocenters, some do not (like allenes), and some molecules with
stereocenters are achiral (meso compounds).
2. Using the Cahn-Ingold-Prelog (CIP) priority rules, which group has the highest priority?
A. -CH2OH
B. -COOH
,C. -CHO
D. -CH2NH2
Answer: B
Conceptual Explanation: Priority is determined by atomic number. -COOH (Carbon
double bonded to O and single bonded to O) ranks higher than -CHO (Carbon double
bonded to O and single bonded to H). -CH2NH2 and -CH2OH rank lower because the first
point of difference involves single bonds to N or O.
3. A solution contains a mixture of two enantiomers with an enantiomeric excess (ee) of 60%
of the (R)-isomer. What is the percentage of the (S)-isomer in the mixture?
A. 40%
B. 60%
C. 30%
D. 20%
Answer: D
Conceptual Explanation: If ee is 60%, then 60% is ‘excess’ R and 40% is the racemic
mixture (equal parts R and S). Therefore, the amount of S is half of the racemic portion:
40% / 2 = 20%.
4. Which statement regarding meso compounds is TRUE?
A. They are optically active due to internal compensation.
, B. They are a type of enantiomer.
C. They must contain at least two stereocenters and a plane of symmetry.
D. They have a non-superimposable mirror image.
Answer: C
Conceptual Explanation: Meso compounds contain stereocenters but are achiral overall
because they possess an internal plane of symmetry or center of inversion, making them
superimposable on their mirror image.
5. How many stereoisomers are possible for 2,3-dibromobutane?
A. 2
B. 3
C. 4
D. 8
Answer: B
Conceptual Explanation: The formula 2^n predicts 4 isomers (n=2 stereocenters), but
because the molecule is symmetrical, one pair of enantiomers is replaced by a single meso
compound. The isomers are (2R,3R), (2S,3S), and the meso (2R,3S) form.
6. Which physical property differs between a pair of pure enantiomers under non-chiral
conditions?
A. Boiling point
