Department of Chemistry
Subject: Chemistry Session: Jan-June 2020
Subject Code: 18BSCH03
Module 3
Question and Answers
Stereochemistry, Organic Reactions and Synthesis of a Drug
Molecule
1. Explain the following
Chirality, Achirality, Enantiomers and Diastereomers
Answer: Chirality: Chirality refers to the any carbon connected to 4 different substitute
groups, sp3hybridised and not having plane symmetry.
Ex:
(2)
Br Br
(4)
H H
C C
I I (1)
F (3) F
Achirality: In 3 dimensional arrangement of every atom is the same and if two molecules
are superimposable then molecule is achiral.
Ex:
Br
H
C
CH3
H3C
Enantiomers: Any molecule is having mirror image and their mirror images are non-
superimposable then they called enantiomers.
Ex:
Br Br
H H
C C
I F
F I
, Diastereomers: Stereoisomers which are not mirror images of each other are called
diastereomers.
Ex:
OH OH
H2
CH H2 CH
C
C
H3C CH CH3 H3C CH CH3
CH3 CH3
3-Methylpentan-2-ol 3-Methylpentan-2-ol
2. Define isomers and explain the classification of isomers.
Answer: Isomers: Compounds having same molecular formula but different structural
arrangement are called Isomers.
Classification of Isomers
3. What is structural and geometrical isomerism with example?
Answer: Structural Isomers
A structural isomer is one in which two or more or organic compounds have the same
molecular formulas but different structures.
Ex: 1-butene and 2-butene show this.
H2 H
H2C H3C C
C C CH3
C CH3 H
H
1-Butene 2-Butene
Geometric Isomers (Stereoisomers)
Geometric isomers are isomers in which the order of atom bonding is the same but the
arrangement of atoms in space is different. Geometric isomers are also referred to
as stereoisomers.
Subject: Chemistry Session: Jan-June 2020
Subject Code: 18BSCH03
Module 3
Question and Answers
Stereochemistry, Organic Reactions and Synthesis of a Drug
Molecule
1. Explain the following
Chirality, Achirality, Enantiomers and Diastereomers
Answer: Chirality: Chirality refers to the any carbon connected to 4 different substitute
groups, sp3hybridised and not having plane symmetry.
Ex:
(2)
Br Br
(4)
H H
C C
I I (1)
F (3) F
Achirality: In 3 dimensional arrangement of every atom is the same and if two molecules
are superimposable then molecule is achiral.
Ex:
Br
H
C
CH3
H3C
Enantiomers: Any molecule is having mirror image and their mirror images are non-
superimposable then they called enantiomers.
Ex:
Br Br
H H
C C
I F
F I
, Diastereomers: Stereoisomers which are not mirror images of each other are called
diastereomers.
Ex:
OH OH
H2
CH H2 CH
C
C
H3C CH CH3 H3C CH CH3
CH3 CH3
3-Methylpentan-2-ol 3-Methylpentan-2-ol
2. Define isomers and explain the classification of isomers.
Answer: Isomers: Compounds having same molecular formula but different structural
arrangement are called Isomers.
Classification of Isomers
3. What is structural and geometrical isomerism with example?
Answer: Structural Isomers
A structural isomer is one in which two or more or organic compounds have the same
molecular formulas but different structures.
Ex: 1-butene and 2-butene show this.
H2 H
H2C H3C C
C C CH3
C CH3 H
H
1-Butene 2-Butene
Geometric Isomers (Stereoisomers)
Geometric isomers are isomers in which the order of atom bonding is the same but the
arrangement of atoms in space is different. Geometric isomers are also referred to
as stereoisomers.
