Semester I
Reaction Mechanism and Stereochemistry (Core II)
Subject Code: PG2012
Unit IV Stereochemistry
Compounds that have the same molecular formula but are not identical are called isomers.
Isomers fall into two main classes: constitutional isomers and stereoisomers. Constitutional
isomers differ in the way their atoms are connected
Eg: ethanol and dimethyl ether are constitutional isomers because they have the same molecular
formula, C2H6O, but the atoms in each compound are connected differently. The oxygen in ethanol
is bonded to a carbon and to a hydrogen, whereas the oxygen in dimethyl ether is bonded to two
carbons.
Stereochemistry is the study of the relative arrangement of atoms or groups in a molecule
in three dimensional space. One important aspect of stereochemistry is stereoisomerism. Isomers
having same chemical formula and bond connectivity but differ in the spatial arrangement of atoms
or groups (configuration) within the molecule are termed as stereoisomers and the phenomenon is
known as stereoisomerism. The Greek word stereo means spatial or three dimensional. Two types
of stereoisomerisms are Optical isomerism and Geometrical isomerism.
, Chirality
An object that is non superimposable on its mirror image and has no plane of symmetry is called
chiral. The property of an object that makes it non superimposable on its mirror image is known
as chirality. “Chiral” comes from the Greek word cheir, which means “hand.”
Look at your left hand and right hand, they look similar, yet a left-handed glove does not fit the
right hand because they are chiral. Why can’t you put your right shoe on your left foot? It is because
feet and shoes have right-handed and left-handed forms and they are chiral. A chiral object has a
non-superimposable mirror image. In other words, its mirror image is not the same as itself. A
hand is chiral because if you look at your left hand in a mirror, you do not see your left hand; you
see only your right hand.
In contrast, a chair is not chiral, it looks the same in the mirror. Objects that are not chiral
are said to be achiral. An achiral object has a superimposable mirror image. Some other achiral
objects are table, fork and glass.
Reaction Mechanism and Stereochemistry (Core II)
Subject Code: PG2012
Unit IV Stereochemistry
Compounds that have the same molecular formula but are not identical are called isomers.
Isomers fall into two main classes: constitutional isomers and stereoisomers. Constitutional
isomers differ in the way their atoms are connected
Eg: ethanol and dimethyl ether are constitutional isomers because they have the same molecular
formula, C2H6O, but the atoms in each compound are connected differently. The oxygen in ethanol
is bonded to a carbon and to a hydrogen, whereas the oxygen in dimethyl ether is bonded to two
carbons.
Stereochemistry is the study of the relative arrangement of atoms or groups in a molecule
in three dimensional space. One important aspect of stereochemistry is stereoisomerism. Isomers
having same chemical formula and bond connectivity but differ in the spatial arrangement of atoms
or groups (configuration) within the molecule are termed as stereoisomers and the phenomenon is
known as stereoisomerism. The Greek word stereo means spatial or three dimensional. Two types
of stereoisomerisms are Optical isomerism and Geometrical isomerism.
, Chirality
An object that is non superimposable on its mirror image and has no plane of symmetry is called
chiral. The property of an object that makes it non superimposable on its mirror image is known
as chirality. “Chiral” comes from the Greek word cheir, which means “hand.”
Look at your left hand and right hand, they look similar, yet a left-handed glove does not fit the
right hand because they are chiral. Why can’t you put your right shoe on your left foot? It is because
feet and shoes have right-handed and left-handed forms and they are chiral. A chiral object has a
non-superimposable mirror image. In other words, its mirror image is not the same as itself. A
hand is chiral because if you look at your left hand in a mirror, you do not see your left hand; you
see only your right hand.
In contrast, a chair is not chiral, it looks the same in the mirror. Objects that are not chiral
are said to be achiral. An achiral object has a superimposable mirror image. Some other achiral
objects are table, fork and glass.
