STEREOCHEMISTRY
, STEREOCHEMISTRY
CONTENTS
4.1 Objectives
4.2 Introduction
4.3 Isomerism
4.4 Structural (Constitutional) Isomerism
4.5 Stereo (Configurational) isomerism
4.5.1 Geometrical Isomerism
4.5.2 Optical Isomerism
4.6 Element of Symmetry
4.7 Stereogenic centre (Stereogenicity)
4.7.1 Optical activity and Enantiomerism
4.7.2 Properties of enantiomerism
4.7.3 Chiral and achiral molecules with two stereogenic centers
4.7.4 Diastereomers
4.7.5 Properties of Diastereomers
4.7.6 Erythro (syn) Threo (anti) diastereomers
4.7.7 Meso compounds
4.8 Relative and absolute configurations
4.8.1 D/L nomenclature
4.8.2 R/S nomenclature
4.8.3 Sequence Rule
4.9 Newman and sawhorse projection formulae
4.10 Fisher flying and wedge formulae
4.11 Racemic mixture (racemates)
4.12 Quasi enantiomers
4.13 Quasi racemates
,4.14 Stereochemistry of allenes, spiranes, biphenyls, ansa compounds, cyclophanes and related
compounds
4.15 Summary
4.16 Terminal Questions
4.17 Answers
4.1 OBJECTIVES
In this unit learner will be able to:
➢ Depict various types of isomerism exhibited by organic compounds and their
representation
➢ Analyze the three dimensional depictions of organic compounds and their two
dimensional representations.
➢ Learn Stereogenicity, chirality, enantiomerism, diastereomerism, their relative and
absolute configurations
➢ Learn about the various stereo chemical descriptors such as (cis-trans, E/Z, D/L, d/l,
erythro/threo, R/S and syn/anti) given to organic molecules differ
➢ Describe the stereochemistry of various rigid and complex molecules like spiranes,
adamentanes, catenanes, cyclophanes etc.
4.2 INTRODUCTION
In undergraduate level chemistry course we have learn about the fundamental concepts of
isomerism and stereochemistry. Isomerism and stereochemistry provides the information about
the different kind of depictions for organic compounds with similar structural formulas.
Chemical compounds are represented by specific structural formulas. These chemical formulas
were first organized by three scientists Kekule, Couper and Butlerov in 1874. The three
dimensional representation of depiction of organic molecules were independently suggested by J
H van’t Hoff and J A LeBel. J H van’t Hoff was honored by Nobel Prize for his work in 1901; he
was the first recipient of Nobel Prize in Chemistry.
, 4.3 ISOMERISM
The word isomerism originated from Greek word isomer (iso= equal; mers = part). When two or
more organic compounds having similar molecular formula but exhibit differences in their
chemical and/or physical properties are called isomers, and the phenomenon is known as
isomerism. However, the stereochemistry of an organic compound can be defined as the
chemistry of that compound in space and as a function of molecular geometry.
Generally isomerism can be divided in to two categories;
a. Structural (constitutional) Isomerism
b. Stereo (configurational) Isomerism
4.4 STRUCTURAL (CONSTITUTIONAL) ISOMERISM
Structural isomerism is also known as ‘constitutional isomerism’. Structural isomerism arises
when a molecule can be represented in to two or more than two different structures. The
difference in structure is due to the difference in the arrangement of atoms within the molecules,
irrespective of their position in space. In other words, structural isomers are compounds those
have identical molecular formulae but different structural formulae; and the phenomenon is
called structural isomerism.
Examples 1: Structural isomer of Butane (C4H10) and Bromobutane (C4H9Br)
CH3CH2CH2CH3 CH3CH2CH2CH2Br
n-Butane 1-Bromobutane
C4H10 C4H9Br
Butane CH3CHCH3 Bromobutane CH3CHCH2CH3
CH3 Br
Isobutane 2-Bromobutane
Structural isomerism can also be subdivided in to five types.
1) Chain Isomerism
2) Functional Isomerism
3) Position Isomerism
, STEREOCHEMISTRY
CONTENTS
4.1 Objectives
4.2 Introduction
4.3 Isomerism
4.4 Structural (Constitutional) Isomerism
4.5 Stereo (Configurational) isomerism
4.5.1 Geometrical Isomerism
4.5.2 Optical Isomerism
4.6 Element of Symmetry
4.7 Stereogenic centre (Stereogenicity)
4.7.1 Optical activity and Enantiomerism
4.7.2 Properties of enantiomerism
4.7.3 Chiral and achiral molecules with two stereogenic centers
4.7.4 Diastereomers
4.7.5 Properties of Diastereomers
4.7.6 Erythro (syn) Threo (anti) diastereomers
4.7.7 Meso compounds
4.8 Relative and absolute configurations
4.8.1 D/L nomenclature
4.8.2 R/S nomenclature
4.8.3 Sequence Rule
4.9 Newman and sawhorse projection formulae
4.10 Fisher flying and wedge formulae
4.11 Racemic mixture (racemates)
4.12 Quasi enantiomers
4.13 Quasi racemates
,4.14 Stereochemistry of allenes, spiranes, biphenyls, ansa compounds, cyclophanes and related
compounds
4.15 Summary
4.16 Terminal Questions
4.17 Answers
4.1 OBJECTIVES
In this unit learner will be able to:
➢ Depict various types of isomerism exhibited by organic compounds and their
representation
➢ Analyze the three dimensional depictions of organic compounds and their two
dimensional representations.
➢ Learn Stereogenicity, chirality, enantiomerism, diastereomerism, their relative and
absolute configurations
➢ Learn about the various stereo chemical descriptors such as (cis-trans, E/Z, D/L, d/l,
erythro/threo, R/S and syn/anti) given to organic molecules differ
➢ Describe the stereochemistry of various rigid and complex molecules like spiranes,
adamentanes, catenanes, cyclophanes etc.
4.2 INTRODUCTION
In undergraduate level chemistry course we have learn about the fundamental concepts of
isomerism and stereochemistry. Isomerism and stereochemistry provides the information about
the different kind of depictions for organic compounds with similar structural formulas.
Chemical compounds are represented by specific structural formulas. These chemical formulas
were first organized by three scientists Kekule, Couper and Butlerov in 1874. The three
dimensional representation of depiction of organic molecules were independently suggested by J
H van’t Hoff and J A LeBel. J H van’t Hoff was honored by Nobel Prize for his work in 1901; he
was the first recipient of Nobel Prize in Chemistry.
, 4.3 ISOMERISM
The word isomerism originated from Greek word isomer (iso= equal; mers = part). When two or
more organic compounds having similar molecular formula but exhibit differences in their
chemical and/or physical properties are called isomers, and the phenomenon is known as
isomerism. However, the stereochemistry of an organic compound can be defined as the
chemistry of that compound in space and as a function of molecular geometry.
Generally isomerism can be divided in to two categories;
a. Structural (constitutional) Isomerism
b. Stereo (configurational) Isomerism
4.4 STRUCTURAL (CONSTITUTIONAL) ISOMERISM
Structural isomerism is also known as ‘constitutional isomerism’. Structural isomerism arises
when a molecule can be represented in to two or more than two different structures. The
difference in structure is due to the difference in the arrangement of atoms within the molecules,
irrespective of their position in space. In other words, structural isomers are compounds those
have identical molecular formulae but different structural formulae; and the phenomenon is
called structural isomerism.
Examples 1: Structural isomer of Butane (C4H10) and Bromobutane (C4H9Br)
CH3CH2CH2CH3 CH3CH2CH2CH2Br
n-Butane 1-Bromobutane
C4H10 C4H9Br
Butane CH3CHCH3 Bromobutane CH3CHCH2CH3
CH3 Br
Isobutane 2-Bromobutane
Structural isomerism can also be subdivided in to five types.
1) Chain Isomerism
2) Functional Isomerism
3) Position Isomerism
