CHEM 219 Module 2 Exam: Stereochemistry and Isomerism
2026/2027 UPDATE
1. What is the relationship between two molecules that are non-
superimposable mirror images of each other?
A. Enantiomers
B. Constitutional isomers
C. Diastereomers
D. Meso compounds
Answer: A
Rationale: Enantiomers are defined as stereoisomers that are non-superimposable mirror
images of one another.
2. How many stereocenters are present in 2-butanol?
A. 0
B. 3
C. 2
D. 1
Answer: D
Rationale: The second carbon in 2-butanol is bonded to four different groups: -H, -OH, -
CH3, and -CH2CH3, making it a single chiral center.
,3. A molecule that contains chiral centers but is achiral due to an internal plane
of symmetry is called a:
A. Racemate
B. Enantiomer
C. Diastereomer
D. Meso compound
Answer: D
Rationale: Meso compounds contain multiple stereocenters but have an internal plane of
symmetry, rendering the entire molecule achiral.
4. According to the Cahn-Ingold-Prelog priority rules, which group has the
highest priority?
A. -OH
B. -CH3
C. -CH2OH
D. -CHO
Answer: A
Rationale: Priority is based on atomic number. Oxygen (in -OH) has a higher atomic
number than carbon (in the other groups).
5. What is the maximum number of stereoisomers possible for a molecule with
3 chiral centers?
A. 3
B. 6
C. 9
D. 8
Answer: D
Rationale: The maximum number of stereoisomers is calculated using the formula 2^n,
where n is the number of chiral centers. 2^3 = 8.
, 6. Which of the following properties differs between a pair of enantiomers in an
achiral environment?
A. Boiling point
B. Density
C. Solubility in water
D. Direction of optical rotation
Answer: D
Rationale: Enantiomers have identical physical properties except for the direction in
which they rotate plane-polarized light and their interactions with other chiral substances.
7. A 50:50 mixture of two enantiomers is known as a:
A. Meso mixture
B. Diastereomeric pair
C. Pure sample
D. Racemic mixture
Answer: D
Rationale: A racemic mixture (or racemate) contains equal amounts of both enantiomers
and shows zero optical rotation.
8. If a chiral compound rotates plane-polarized light in a clockwise direction, it is
termed:
A. Levo-rotatory (-)
B. Syn-rotatory
C. Dextro-rotatory (+)
D. Anti-rotatory
Answer: C
Rationale: Dextrorotatory (+) substances rotate light clockwise, while levorotatory (-)
substances rotate light counter-clockwise.
2026/2027 UPDATE
1. What is the relationship between two molecules that are non-
superimposable mirror images of each other?
A. Enantiomers
B. Constitutional isomers
C. Diastereomers
D. Meso compounds
Answer: A
Rationale: Enantiomers are defined as stereoisomers that are non-superimposable mirror
images of one another.
2. How many stereocenters are present in 2-butanol?
A. 0
B. 3
C. 2
D. 1
Answer: D
Rationale: The second carbon in 2-butanol is bonded to four different groups: -H, -OH, -
CH3, and -CH2CH3, making it a single chiral center.
,3. A molecule that contains chiral centers but is achiral due to an internal plane
of symmetry is called a:
A. Racemate
B. Enantiomer
C. Diastereomer
D. Meso compound
Answer: D
Rationale: Meso compounds contain multiple stereocenters but have an internal plane of
symmetry, rendering the entire molecule achiral.
4. According to the Cahn-Ingold-Prelog priority rules, which group has the
highest priority?
A. -OH
B. -CH3
C. -CH2OH
D. -CHO
Answer: A
Rationale: Priority is based on atomic number. Oxygen (in -OH) has a higher atomic
number than carbon (in the other groups).
5. What is the maximum number of stereoisomers possible for a molecule with
3 chiral centers?
A. 3
B. 6
C. 9
D. 8
Answer: D
Rationale: The maximum number of stereoisomers is calculated using the formula 2^n,
where n is the number of chiral centers. 2^3 = 8.
, 6. Which of the following properties differs between a pair of enantiomers in an
achiral environment?
A. Boiling point
B. Density
C. Solubility in water
D. Direction of optical rotation
Answer: D
Rationale: Enantiomers have identical physical properties except for the direction in
which they rotate plane-polarized light and their interactions with other chiral substances.
7. A 50:50 mixture of two enantiomers is known as a:
A. Meso mixture
B. Diastereomeric pair
C. Pure sample
D. Racemic mixture
Answer: D
Rationale: A racemic mixture (or racemate) contains equal amounts of both enantiomers
and shows zero optical rotation.
8. If a chiral compound rotates plane-polarized light in a clockwise direction, it is
termed:
A. Levo-rotatory (-)
B. Syn-rotatory
C. Dextro-rotatory (+)
D. Anti-rotatory
Answer: C
Rationale: Dextrorotatory (+) substances rotate light clockwise, while levorotatory (-)
substances rotate light counter-clockwise.
