What is geometrical isomerism? What is its cause? Give examples.

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 Multiple Choice QuestionsShort Answer Type

121.

What are alkenes ?

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122.

What kind of structural isomerism is shown by alkenes ?

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 Multiple Choice QuestionsLong Answer Type

123.

Write IUPAC names of the following compounds:


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124.

Give IUPAC names of the following compounds:
(a) CH3CH = (CH3)2
(b) CH2 = CH – C ≡ C – CH3


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 Multiple Choice QuestionsShort Answer Type

125.

Calculate the number of sigma (σ) and pi open parentheses straight pi close parentheses bonds in the following structures:






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 Multiple Choice QuestionsLong Answer Type

126.

Write structure and IUPAC names of different structural isomers of alkenes corresponding to C5H10

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127.

What is meant by hindered (or restricted) rotation around carbon-carbon double bond? What type of isomerism does it lead to?

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128.

What is geometrical isomerism? What is its cause? Give examples.


When the same molecular formula represents two compounds which differ in the spatial arrangement of atoms or groups around carbon-carbon double bond, then such isomers are called geometrical isomers. The phenomenon is called geometrical isomerism. 

Cause of geometrical isomerism: Geometrical isomerism is due to the restricted or hindered rotation around the carbon-carbon double bond. Due to the hindered rotation around carbon-carbon double bond, the relative positions of atoms or group attached to the doubly bonded carbon atoms get fixed. For example, the molecular formula C2A2B2with the structural formula BAC=CAB represents two geometrical isomers.



Isomer in which similar atoms or groups lie on the same side of the double bond is called cis-isomer. The geometrical isomer I represent a cis-isomer. Isomer in which the similar atoms or groups lie on the opposite sides of the double bond is called trans-isomer. The geometrical isomer (ii) represents a trans-isomer. Hence, geometrical isomerism is known as cis-trans isomerism e.g.

(i) But-2-ene exhibits geometrical isomerism.




(ii) Hex-3-ene shows geometrical isomerism.



(iii) 1, 2-dichloroethene exhibits geometrical isomerism.



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 Multiple Choice QuestionsShort Answer Type

129.

What are the necessary and sufficient conditions for a compound to exhibit geometrical isomerism ?

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130.

Name the various structural isomers possible in C4H8. Which one will exhibit geometrical isomerism?

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