GEOMETRICAL ISOMERISM

               Geometrical isomerism 

The isomerism which due to restricted or forzen rotation about a bond in a molecular is k/as Geometrical isomerism.

Pharmacygyan by NITESH VISHWKARMA

The rotation either about a double bond or about single bond or in a cyclic compound can be seen.

Geometrical isomerism is exhibited by variety of compound lile
--- Compound Containing a double bond
(C=C) (C=N) (N=N)

Compound containing cyclic structure homocyclic Or hetrocylic.

Compound having restricted rotation about a single bond. Due to steric hindrance in biphenyl compound.

CONDITION FOR GEOMETRICAL ISOMERISM
A compound will show geometrical if it fulfill following three conditions.

1- There should be atleast one double bond            b/w and carboy, carbon and nitrogen.
2- There should be restricted rotation in                  double bond.
3- There should be at lest one similar group             b/w both double bond carbon.

NOMENCLATURE OF GEOMETRICAL ISOMERISM

GEOMETRICAL ISOMERISM can be nomenclature by 3 method -:

1. Cis- trans nomenclature
2. E and Z nomenclature
3. Syn and Anti nomenclature

1. CIS TRANS NOMENCLATURE

*There should be atleast one double bond b/w C=C, C=N.
*There should be restricted rotation in double bond.
*Tere should be atleast one similar group b/w both double bond carbon.
*If the similar atom are group is present on the same axis an both carbon then it is called CIS ISOMER and if they are present on opposite axis then they are TRANS ISOMER.

2. E and Z NOMENCLATURE

*There should be atleast one double bond b/w carbon and C, C and N or N and N.
*Four atoms or group which are held with both carbon should be different.
*There should be restricted in rotation.  E and Z is the derived from two Jarmon words -:

Z – ZUSSAMAN – CIS (SOME SIDE)
E – ENTEGGEN – TRANS (OPPOSITE SIDE)

EXAMPLE –
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3. SYN – ANTI NOMENCLATURE

*This kind of isomerism is shown by those compound which have atleast one  C=N OR N=N.

It is of two types

1. SYN – SAME  SIDE – CIS
2. ANTI – OPPOSITE – TRANS

*If the heigher polar group is present on the same side of carbon and nitrogen atom then it is called SYN and if height polar group are present an opposite side then is called ANTI.

*Determination of configuration of geometrical isomerism.

There are a number of method to determine the configuration of geometrical isomerism. 

1. Physical method
2. Cyclisation method
3. Conversion method 

1.Physical method -: The melting point and intently of absorption of cis isomer are lower than trans.
* The boiling point solubility heat of combution heat of hydrogenation, densiy, reflective index, dipole movement and dissociation constant of cis are greater then trans isomer.
By the comparison of above there physical properties we can determine the configuration of isomers.

2.Cyclisation Method -: Intermolecular reaction are more likely to occurs the closer together are the reaction group in the molecular, cis isomer undergoess the cyclisation reaction bit the trans isomer does not go for cyclisation reaction.

Ex. Malic acid after dehydration gives a cyclic compound maloc anhydride but fumaric acid do not gives dehydrated reaction so molic acid is cis isomer and feumeriv acid is trans isomer.

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3.Conversion method -: In this method unkown compound is convert compound after chemical reaction conversion method we can configuration of compound.

Ex. If tri chloro erotenic after oxidation gives fumeric acid then it is trans and if it gives malic acid then it is cis isomers.

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