Post on 12-Nov-2014
SINHA I. I.T. CHEMISTRY
1-D 10 TALWANDI, KOTA 09314905055
How to identify Geometrical Isomers. Organic compounds which have same molecular formula but different non-interchangable geometry due to different orientation of atoms in space are called Geometrical Isomers. Example.
CH3
H
CH3
H
CH3
H
H
CH3
cis-but-2-ene trans)-but-2-ene Geometrical Isomers are
1. different compounds i.e non-superimposable i.e. cannot be interconverted without bond dissociation
2. A type of configurational isomers i.e. they differs in orientation at least at one carbon atom. Or ( stereo center)
3. Being isomers they have same molecular formula , empirical formule , % composition 4. They have a defined geometry. 5. As they geometrically differs therefore have different dipole moments , mp, bp, vapour
pressure , solubility. Geometrical Isomerism is found in compounds which have
a. Planner geometry (real or virtual) b. Different substituent on either side of imaginary or real planner geometry. c. No interconvertibility ( Presence of Pi bond , continuous pi bond etc.
Planner geometry (real or virtual) :-It is found in following cases.
1. Alkene.
CH3
H
H
CH3
sp2
carbon
2.Alkene (cumulene with odd no of pi bonds)
CH3
HC C CH3
H .
CH3
HC C CH3
H X
Y
ZZYY
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SINHA I. I.T. CHEMISTRY
1-D 10 TALWANDI, KOTA 09314905055
3 Cycloalkanes
CH3
H
CH3
H
XZ plane
4. Odd no Spiranes
CH3CH3
HH 5.Odd no combination of spiro & cumulene
CH3CH3
H H
6.Cycloalkene with carbon greater than 8
H
H
H
Hcis trans 7 Fused rings also have cis & trans orientation
H
H
cis
CH3
CH3
trans
Notation system:
1. cis & trans. 2. Syn and anti 3. E & Z. 1. cis & trans cis and trans notation is used only if there are two identical groups on either
side of the planer geometry.
Ex. cis trans none 2. Syn and Anti notation is used only if there are C=N or N=N bond with different
substituents ( Historical approach used by fisher for Oximes).
SINHA I. I.T. CHEMISTRY
1-D 10 TALWANDI, KOTA 09314905055
Ex.
N
OHCH3
H
N
OHH
CH3
N
OHCH3
CH3anti syn none
N N
CH3CH3
syn
N N
CH3
CH3anti
3.E and Z notations are introduced to designate geometrical isomers of any type.
Ex.
Cl
Br
CH3
H
Br
Cl
CH3
HE Z1.
1. 1. 1.
1. represent high priority group No. of geometrical units and no of geometrical isomers. Total no of geometrical isomers depends on 1. no of geometrical units 2. symmetry/ unsymmetry 3. other structural limitations.
Ex.
CH3
CH3
C C CH3
CH3
CH3
1.
CH3
H
C C CH3
CH3
CH3
2.
CH3
H
C C H
H
CH3
3.
C H 3
H
C H 3
H
CH 3
H
CH 3
H4.
CH3
H
CH3
H
CH3
H
5.
6.CH3
H
CH3
CH3
H
7.
CH3
H
CH3
H
8.
CH3
H
CH3
H
CH3 H
CH3 H
SINHA I. I.T. CHEMISTRY
1-D 10 TALWANDI, KOTA 09314905055
9.
CH3
H
CH3
H H
H
CH3
CH3
H
10
CH3
H
CH3
H
C C
H
C C
H
CH3
H
CH3
H
11. H
CH3
HH
CH3
H
12. H
CH3
H
CH3
HCH3
HH
13.14. 15.