The document provides an introduction to stereochemistry, which is the study of three-dimensional arrangements of atoms in molecules. It discusses how stereoisomers can have the same molecular formula but different spatial arrangements. The importance of stereochemistry is highlighted using the examples of starch and cellulose, which are stereoisomers that have different properties. The document also summarizes the thalidomide disaster which demonstrated the significance of stereochemistry due to different biological effects of stereoisomers. Key concepts like chiral carbon, enantiomers, diastereomers, and optical activity are defined.

1. BASICS OF
STEREOCHEMISTRY
PRESENTED BY- MANISHA
M.SC. PHAMA. CHEM.
HNBGU(CENTRAL UNIVERSITY)

2. INTRODUCTION
• Stereochemistry is the branch of chemistry that involves “the study of the different spatial arrangement
of atoms in molecules.
• The structure of a molecule can vary based on the 3d arrangement of the atoms that constitute it.
• The branch of chemistry is commonly referred to as 3-D chemistry since it focuses on stereoisomers
(chemical compounds with the same molecular formula but different spatial arrangement in three
dimensions).
• One of the branches of stereochemistry deals with the study of molecules that exhibit chirality,which is a
geometric property of molecules that make them non superimposable on their mirror images.
• Another branch of 3-D chemistry known as dynamic stereochemistry,involves the study of the effect of
different spatial arrangemets of atoms in molecules on the rate of a chemical reaction.

3. HOW IMPORTANT IS STEREOCHEMISTRY?
Example 1– starch and cellulose are two polymers that belong to the
family of biomolecules called carbohydrate.
Cellulose and starch are both composed of the same repeating unit.
Starch and cellulose are isomers because they are different compounds
with the same molecular formula(C6H10O5)n
They are stereoisomers because only the three dimensional
arrangement of atoms is different.

4. FUNDAMENTAL DIFFERENCE IN CELLULOSE
AND STARCH
• In cellulose the oxygen
atom join two ring using
two equatorial bonds.
• In starch the oxygen
atom join two ring using
one equatorial and and
one axial bond.

6. THALIDOMIDE DISASTER
• An example of the significance of stereochemistry can be observed in the thalidomide disaster
that struck Germany in the year 1957.
• The drug thalidomide was sold as an over the counter drug,initially intended to combat
nausea.it was used by pregnant women to alleviate morning sickness.
• However it was discovered that the drug underwent racemization and formed a mixture of
enantiomers in the human body due to the process of metabolism.
• One of these enantiomers is believed to cause genetic damage in developing embroys and lead
to birth defect in babies.
• This is based on the data that over 5000 babies were born with deformed limbs shortly after
thalidomide was commercially sold as an over the counter drug.
• This unforeseen effect of the drug led to the imposition of stricter drug regu;ation laws (only
40% of the babies born with these deformities survived).
• The disaster signifies the importance of stereochemistry.

7. THE TWO MAJOR CLASSES OF ISOMERS
constitutional isomers
• Differ in the way the atoms are
connected to each other.
• Have different IUPAC name.
• Have same or different functional
groups.
• Have different physical properties,so
they are separable by physical
technique such as distillation.
• Have different chemical properties.

8. STEREOISOMERS[STEREO=SPACE]
• Differ only in the way atoms are oriented in
space.
• Stereisomers have identical IUPAC names
(except for a prefix like cis or trans).
• Same physical properties because they differ
only in the 3d arrangement of atoms.
• Stereoisomers always have the same functional
groups.

9. SUBDIVISION OF ISOMERS

10. CONFORMATIONAL ISOMERS
• Structure that can be interconverted simply by rotation about sigma bonds
are conformation of the same molecules.
CONFIGURATIONAL ISOMERS
• Structure that can be interconverted only by breaking the bonds have
different configuration and are stereoisomers.

11. GEOMETRICAL ISOMERS:
• These isomers result from restricted rotation ,restricted rotation can be
caused by either a cyclic structure or a double bond.
Conditions of geometrical isomers:
A) GEOMETRICAL ISOMERISM arises due to the presesnce of a double bond
or a ring structure.

12. CASE 2
• Different group should be
attached at each doubly bonded
atom.

13. 3
• Geometrical isomers are also called configurational isomers. Geometrical
isomers are two different compounds.

14. Pi bond lock the molecule. And
this, restrict the rotation around
the carbon carbon double bond or
is responsible for the geometric
isomerism in alkene.

15. CIS AND TRANS ISOMER
If the two similar groups are on same side of restricted bond (double bond)the
configuration is cis otherwise trans.
Cis and trans isomer can be separate from each other because they are
different compounds with different physical properties for example they have
different boiling point and a different dipole moment.

16. E,Z NAMING IN GEOMETRICAL
NOMENCLATURE:
E (short for german Entegegen which means
“opposite)
Z(short for german Zusamen which means
“together”)
If the two senior group are on same side of
restricted bond the configuration is Z otherwise E.

17. SEQUENCE RULE(CAHN-INGOLD-PRELOG
OR CIP RULE)
For deciding the seniority of groups following (CIP)rules are applied.
Rule 1– the group with the first group having higher atomic no.is senior.
according to this rule the seniority of atom is:
I > Br > Cl > S > F > O > N > C > H
Rule 2- the higher mass isotope is senior:
thus a) T > D > H
Rule 3- if the first group is identical then second atom is observed for
seniority:.
example: -CH2Cl > -CH2OH > -CH2NH2 > CH2CH3 > CH3

18. Rule 4- to assign a priority to an atom that is part of a
multiple bond treat a multiply bonded atom as an
equivalent no.Of singly bonded atom.

20. OPTICAL ISOMERISM
• The phenomenon of rotating the plane
polarized light is known as optical activity and
the compound exhibiting this property are
known as optically active compounds.
• In other words, compounds which have similar
chemical and physical properties and differ
only in their optical activity i.e. their behaviour
towards plane polarized light are known as
optical isomers and the phenomenon as optical
isomerism.

21. 1- plane polarized light: according to physical theory,an ordinary
ray of light vibrates in all plane.
when this light is passed through a nicol prism its vibrations in all
planes, except one are either rejected or absorbed and thus the
emergent beam vibrates only in one direction.such type of light
whose vibrations occur only in a single plane is known as plane
polarized light and the phenomenon is known as polarization.
when plane polarized light is passed through certain substances or
their solution,or plane of polarization is rotated either towards
right (clockwise) or towards left (anti-clockwise)by a certain angle.

22. Such substance which rotate the plane polarized light are
known as optically active and the phenomenon is referred to
as optical activity.
On the basis of the study of optical activity ,the various
organic compounds are divided into three types:
1- dexotro-rotatory (latin dexter=right) d or (+) form
it rotates the plane polarized light to right.
2- laevo-rotatory( latin laevous=left) l or (-) form
it rotates the plane polarized light to the left.
3-optically inactive componds : these compounds
don’t rotate the plane polarized light in any direction.

23. The magnitude of rotation depends upon the following
factors:
1-nature of the substance.
2-Concentration of the solution.
3-Tempreture of solution.
4-Wavelength of the light used.
2- specific rotation- the measurement of optical activity is
reported in terms of specific rotation which is constant.
Specific rotation as much a characterstics for a particular
compound as its m.P. B.P. Etc.
Formula:

25. Optical isomers classified into two types:
1- enantiomers
2- diastereomers
Enantiomers: when two isomers are the non superimposable mirror
image of each other. These are known as enantiomers.
Identical physical properties such as m.P. B.P. , Densities and refractive
indices etc.
Differ only in their action on plane polarized light.
Example: lactic acid

27. RECEMIC
MIXTURE:
When two enantiomers are
mixed in equimolar quantities,
it results in the formation of
an optically inactive
compound called racemic,dl or
(+-) form.
Thus if equal amount of d lactic
acid and l lactic acid mixed
together,it will produce optically
inactice or racemic lactic acid.
Recemic mixture has some
physical properties different from
those of the two enantiomers .

28. CHARACTERSTICS OF DIASTEREOMERS
• When the configurational isomers are
not mirror image of each other these
are known as diastereomers
• Different physical properties such as
m.p. b.p. densities ,refractive indices
and specifc rotation.
• It may or may not be optically active.

29. Concept of chirality
• A molecule or object that is not superimposable on its mirror image is said to be
chiral .
• Example left hand and right hand are mirror image of each other but they are not
superimposable.

30. CHIRALITY :CAUSE OF OPTICAL ACTIVITY
• On studying the structure of several optically active compound it was observed that
most of them contain at least one chiral carbon atom.
chiral carbon: a carbon atom having four different monovalent
atoms or groups is known as chiral carbon or chiral centre.
The term chiral is derived from the Greek word ‘cheir’ means hand. Similarly the
term chirality means handeness in reference to our two hands, each of which is the
non superimposable mirror image of each other.

31. Thus we can say that the term chiral and chirality are used in reference
to compounds whose mirror image is non superimposable over itself.
1– many but not all molecules that contain chiral centre are chiral.
Example: LACTIC ACID
2- thus there are molecules that although contain chiral centre yet
are achiral .

32. 3– some chiral molecules do not have any chiral centre example: 2,3
pentadiene
thus the presence or absence of a chiral centre is no criterion of
chirality thus the presence of achiral centre indicates only the
possibility of chirality in the molecule.