isomerism

1. CHEMISTRY PRESENTATION
BY:-MOIN KHAN HUSSAIN
UID:-14BBT1129

2. Isomerism

3. Isomerism
ISOMERS are compounds with the same
molecular formula
(but different arrangements of atoms)

4. Types of Isomerism
1. Structural isomerism
2. Stereoisomerism
• Geometric (cis/trans)
• Optical

5. 1. Structural isomerism

6. Structural Isomerism
C2H6O
These two compounds areThese two compounds are
structural isomersstructural isomers
methoxymethane
ethanol

7. Structural Isomerism
CH3
N
+
O
-
O CH3
N
+
O
-
O
Structural isomers often have differentStructural isomers often have different
chemical & physical propertieschemical & physical properties
CH3
N
+
O
-
O
o– m– p–
–nitromethylbenzene

8. Exercise
Q What two compounds, with different
functional groups, are isomers with the
formula:
C3H6O2

9. Answer
A carboxylic acid
CH3 OH
O
CH3
O
CH3
O
An ester

10. 2. Stereoisomerism
a. Geometric isomerism

11. Geometric Isomerism (cis/trans)
If two compounds have the same formulae
and the same structural framework,
but differ in the spatial arrangement of
different atoms or groups about a central
atom

12. CH3CH3
H H
CH3
CH3
H
H
Geometric Isomerism (cis/trans)
or about a double bond,

13. Geometric Isomerism (cis/trans)
then the compounds are called GEOMETRIC
ISOMERS
– Cis– on the same side
– Trans– on the opposite side

14. Geometric Isomerism (cis/trans)
[Pt(NH3)2Cl2]
CisCis––diamminedichloroplatinum(II)diamminedichloroplatinum(II) TransTrans––diamminedichloroplatinum(II)diamminedichloroplatinum(II)

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Geometric Isomerism (cis/trans)
There is restricted rotation
about a C=C double bond
and the two isomers are not
inter-convertible without
first breaking the C=C bond
Cis-but-2-ene
Trans-but-2-ene
CH3CH3
H H
CH3
CH3
H
H

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Geometric isomerism helps you see!
This reaction is the central feature of human visionThis reaction is the central feature of human vision
11-cis-retinal 11-trans-retinal
11 12
R R’
R’
11 12
R
Cis Trans
O
CH3
CH3CH3
CH3
CH3
H
O
CH3
CH3CH3
CH3 CH3 H
L i g h t

17. 2. Stereoisomerism
b. Optical isomerism

18. Optical Isomerism
Optical isomerism is caused by a lack of
symmetry in a molecule’s structure so that
the molecule and its mirror image are
actually different
–like a left hand and a right hand:
They are non-superimposable

19. For example
Nonsuperimposable
mirror images
Optical isomers
are called
ENANTIOMERENANTIOMER
SS

20. Enantiomers
Labels L– and D– are given to
two enantiomers to
distinguish them from each
other
OH
OH O
OHNH2
H
Only one optical
isomer of DOPA
called L-DOPA, is
effective in the
treatment of
Parkinson’s disease

21. Asymmetric Carbon
A compound that is NOT SUPERIMPOSABLE
on its mirror image is described as being
CHIRAL
Many chiral compounds contain an
asymmetric carbon atom – a carbon atom
with FOUR different groups attached

22. CHIRAL Carbon

23. For example – limonene
CH3
CH2
CH3
H
Lemons Oranges
CH3
CH2
CH3
H

24. For example – limonene
Lemons Oranges
CHIRAL CCHIRAL C