STEREOISOMERISM.•GEOMETRICAL ISOMERISM •OPTICAL ISOMERISM PPT/PDF

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Description

Course Code: BP401T

Course Title: Pharmaceutical Organic Chemistry III

Stereoisomerism

 

Session Objectives

By the end of this session, students will be able to:

➢ Explain the types of stereoisomerism

➢ Geometrical isomerism

➢ Optical isomerism

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STEREOISOMERISM

Molecules have the SAME MOLECULAR FORMULA but the atoms are joined to
each other in a DIFFERENT SPACIAL ARRANGEMENT – they occupy a different
position in 3-dimensional space.

There are two types…

•GEOMETRICAL ISOMERISM

•OPTICAL ISOMERISM

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GEOMETRICAL ISOMERISM IN ALKENES

Introduction

• an example of stereoisomerism
• found in some, but not all, alkenes
• occurs due to the RESTRICTED ROTATION OF C=C bonds
• get two forms…

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GEOMETRICAL ISOMERISM IN ALKENES
Introduction

• an example of stereoisomerism
• found in some, but not all, alkenes
• occurs due to the RESTRICTED ROTATION OF C=C bonds
• get two forms…

CIS (Z)
Groups/atoms are on the TRANS (E)
SAME SIDE of the double Groups/atoms are on

bond OPPOSITE SIDES across
the double bond

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GEOMETRICAL ISOMERISM

RESTRICTED ROTATION OF C=C BONDS

Single covalent bonds can easily rotate. What appears to be a different
structure is not. It looks like it but, due to the way structures are
written out, they are the same.

ALL THESE STRUCTURES ARE THE SAME BECAUSE C-C BONDS HAVE ‘FREE’ ROTATION

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GEOMETRICAL ISOMERISM

RESTRICTED ROTATION OF C=C BONDS

C=C bonds have restricted rotation so the groups on either end of the
bond are ‘frozen’ in one position; it isn’t easy to flip between the two.

This produces two possibilities. The two structures cannot interchange easily
so the atoms in the two molecules occupy different positions in space.

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GEOMETRICAL ISOMERISM IN ALKENES

E/Z or CIS-TRANS

E / Z Z (zusammen) higher priority groups / atoms on
the SAME side of C=C bond

E (entgegen) higher priority groups / atoms on
OPPOSITE sides of C=C bond

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GEOMETRICAL ISOMERISM IN ALKENES

E/Z or CIS-TRANS

E / Z Z (zusammen) higher priority groups / atoms on
the SAME side of C=C bond

E (entgegen) higher priority groups / atoms on
OPPOSITE sides of C=C bond

To determine priority, the Cahn, Ingold and Prelog convention is used.

eg C2H5 > CH3 > H and I > Br > Cl > F > C > H

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GEOMETRICAL ISOMERISM IN ALKENES

E/Z or CIS-TRANS

E / Z Z (zusammen) higher priority groups / atoms on
the SAME side of C=C bond

E (entgegen) higher priority groups / atoms on
OPPOSITE sides of C=C bond

To determine priority, the Cahn, Ingold and Prelog convention is used.

eg C2H5 > CH3 > H and I > Br > Cl > F > C > H

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GEOMETRICAL ISOMERISM IN ALKENES

E/Z or CIS-TRANS

E / Z Z (zusammen) higher priority groups / atoms on
the SAME side of C=C bond

E (entgegen) higher priority groups / atoms on
OPPOSITE sides of C=C bond

To determine priority, the Cahn, Ingold and Prelog convention is used.

eg C2H5 > CH3 > H and I > Br > Cl > F > C > H

E Z Z E

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GEOMETRICAL ISOMERISM IN ALKENES

E/Z or CIS-TRANS

CIS / Should only be used when there are two H’s and two
TRANS non-hydrogen groups attached to each carbon.

cis non-hydrogen groups / atoms on the
SAME side of C=C bond

trans non-hydrogen groups / atoms on
OPPOSITE sides of C=C bond

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GEOMETRICAL ISOMERISM IN ALKENES

E/Z or CIS-TRANS

CIS / Should only be used when there are two H’s and two
TRANS non-hydrogen groups attached to each carbon.

cis non-hydrogen groups / atoms on the
SAME side of C=C bond

trans non-hydrogen groups / atoms on
OPPOSITE sides of C=C bond

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GEOMETRICAL ISOMERISM IN ALKENES

E/Z or CIS-TRANS

CIS / Should only be used when there are two H’s and two
TRANS non-hydrogen groups attached to each carbon.

cis non-hydrogen groups / atoms on the
SAME side of C=C bond

trans non-hydrogen groups / atoms on
OPPOSITE sides of C=C bond

cis trans cis trans

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GEOMETRICAL ISOMERISM

Isomerism in butene

There are 3 structural isomers of C4H8 that are alkenes*. Of
these ONLY ONE exhibits geometrical isomerism.

but-1-ene cis but-2-ene trans but-2-ene 2-methylpropene
(Z) but-2-ene (E) but-2-ene

*

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GEOMETRICAL ISOMERISM

How to tell if it exists

Two different Two different
atoms/groups atoms/groups GEOMETRICAL ISOMERISM

attached attached

Two similar Two similar
atoms/groups atoms/groups

Once you get two similar
attached attached

atoms/groups attached to
one end of a C=C, you

Two similar Two different cannot have geometrical

atoms/groups atoms/groups isomerism
attached attached

Two different Two different
atoms/groups atoms/groups GEOMETRICAL ISOMERISM

attached attached

 

summary
• Stereo isomers are molecules have the SAME MOLECULAR FORMULA but the

atoms are joined to each other in a DIFFERENT SPACIAL ARRANGEMENT – they
occupy a different position in 3-dimensional space.

• Stereoisomers are of two types: Geometrical isomerism & Optical isomerism
• Geometrical isomerism occurs due to the RESTRICTED ROTATION OF C=C bonds

• C=C bonds have restricted rotation so the groups on either end of the bond are
‘frozen’ in one position; it isn’t easy to flip between the two.

• Groups/atoms are on the SAME SIDE of the double bond – CIS (Z)
• Groups/atoms are on OPPOSITE SIDES across the double bond – TRANS (E)
• Higher priority groups / atoms on the SAME side of C=C bond Z (zusammen)
• higher priority groups / atoms on OPPOSITE sides of C=C bond E(entgegen

 

Disclaimer

All data and content provided in this presentation are
taken from the reference books, internet – websites
and links, for informational purposes only.

 

Thank You
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