This document discusses isomerism in organic chemistry. It defines isomers as molecules with the same empirical formula but different connectivity of atoms. There are two main types of isomers: constitutional isomers, which have different carbon skeletons or functional groups, and stereoisomers, which have the same connectivity but different 3D orientations. Stereoisomers include enantiomers, which are non-superimposable mirror images, and diastereomers, which are non-mirror-image forms. It also discusses the chirality of molecules that are non-superimposable on their mirror images and how the different stereoisomers of chiral drugs can have different biological effects.

1. BIO-ORGANIC
CHEMISTRY
Lesson 2
INTRODUCTION
Objectives:
1. Define isomerism.
2. Distinguish the different types of isomers present in
carbon chains.
3. Draw structural formulas of various isomers.
4. Define chirality and optical activity.
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2. BIO-ORGANIC
CHEMISTRY ISOMERISM
Lesson 2
DEFINE ISOMERS
INTRODUCTION
Isomers refer to two or more molecules that have the same
empirical formula but the individual atoms are connected in
different ways, leading to different molecules.
molecules
ISOMERS
Stereoisomers Constitutional Isomers
Enantiomers Diastereomers
(mirror-image) (non-mirror-image)
Configurational cis - trans
diastereomers diastereomers
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3. BIO-ORGANIC
CHEMISTRY ISOMERISM
Lesson 2
CONSTITUTIONAL ISOMER
INTRODUCTION
It has different connections among atoms.
Skeletal – different carbon skeleton
n- PENTANE ISOPENTANE
Functional – different functional groups
CH3CH2OH CH3OCH3
alcohol ether
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4. BIO-ORGANIC
CHEMISTRY ISOMERISM
Lesson 2
CONSTITUTIONAL ISOMER
INTRODUCTION
It has different connections among atoms.
Positional- different position of functional
groups
NH2 H2
C C NH2
H3C H CH3 H3C C
H2
ISOPROPYLAMINE
PROPYLAMINE
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5. BIO-ORGANIC
CHEMISTRY ISOMERISM
Lesson 2
STEREOISOMERS
INTRODUCTION
It involves same connections among atoms but different
geometry.
Enantiomers- non-superimposable mirror – image.
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6. BIO-ORGANIC
CHEMISTRY ISOMERISM
Lesson 2
STEREOISOMER
INTRODUCTION
It has same connections among atoms but different geometry.
Diastereomers- non-superimposable non-mirror – image.
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7. BIO-ORGANIC
CHEMISTRY ISOMERISM
Lesson 2
STEREOISOMERS
INTRODUCTION
It involves same connections among atoms but different
geometry.
Cis-trans: substituents on same side or opposite side of
ring or double bond.
http://www.uwplatt.edu/~sundin/354-7/l547-08.htm#CYCLO
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8. BIO-ORGANIC
CHEMISTRY CHIRALITY (ky-ral; Greek cheir; meaning “hand”)
Lesson 2
It is when molecules are optically active…
INTRODUCTION
http://www.novactabio.com/biotrans.php
Chiral image from Amino Acid Dating at http://www.creation-science-prophecy.com/amino/
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9. BIO-ORGANIC
CHEMISTRY Chemistry connection
Lesson 2
Chiral Drugs
Just as various stereoisomeric forms of a chiral molecule have different physical
INTRODUCTION
properties, these stereoisomers manifests different biological properties. More dramatic
examples of how a change in isomerisms can affect the biological properties of molecules
are found in drugs . A more commonly prescribed medicine, Prozac where the racemic
fluoxetine is extraordinarily effective as antidepressant but it has no activity against
migraine. While the pure S- enantiomer however works remarkably well in preventing
migrane.
Drugs that come from natural sources, either directly or after chemical modification, are
usually chiral and are generally found as a single enantiomer rather then the racemic
mixture. Penicillin V, is an antibiotic isolated from Penicillium mold.
This drug has a 2S, 5R, 6R configuration.
To become biologically active, chiral molecules must fit into a chiral receptor at the target
site, similar to hands fitting into gloves. Just as left hand can fit only into a left-hand glove,
so as a particular stereoisomer can fit only into a receptor with proper complementary
SOURCE: Adapted from Fundamentals shape.
of Organic
Chemistry by J. McMurry, 5th ed., 2003
(S)-Fluoxetine
Penicillin V
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10. BIO-ORGANIC
CHEMISTRY Chemistry connection
Lesson 2
Chiral Drugs
Just as various stereoisomeric forms of a chiral molecule have different physical
INTRODUCTION
properties, these stereoisomers manifests different biological properties. More dramatic
examples of how a change in isomerisms can affect the biological properties of molecules
are found in drugs . A more commonly prescribed medicine, Prozac where the racemic
fluoxetine is extraordinarily effective as antidepressant but it has no activity against
migraine. While the pure S- enantiomer however works remarkably well in preventing
migrane.
Drugs that come from natural sources, either directly or after chemical modification, are
usually chiral and are generally found as a single enantiomer rather then the racemic
mixture. Penicillin V, is an antibiotic isolated from Penicillium mold.
This drug has a 2S, 5R, 6R configuration.
To become biologically active, chiral molecules must fit into a chiral receptor at the target
site, similar to hands fitting into gloves. Just as left hand can fit only into a left-hand glove,
so as a particular stereoisomer can fit only into a receptor with proper complementary
SOURCE: Adapted from Fundamentals shape.
of Organic
Chemistry by J. McMurry, 5th ed., 2003
(S)-Fluoxetine
Penicillin V
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