What is meant by hindered (or restricted) rotation around carbon

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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?


Hindered rotation about double bond: The carbon-carbon double bond in ethylene and other compounds consists of a σ bond and a  bond. The  bond involves the overlapping of unhybridized p-orbitals of two carbon atoms above and below the plane of the atoms. Because of this type of overlapping, rotation around carbon-carbon double bond is strongly hindered and can do so only if the  bond breaks. The breaking of the  bond requires about 284 kJ of energy per mole which is not available to the molecule at room temperature. Hence, the atoms or groups attached to each carbon atom can not rotate about it. The rotation about the double bond is, therefore, restricted or hindered.

Isomerism due to hindered rotation: Due to hindered rotation around carbon-carbon double bond, the relative positions of groups attached to the double bonded carbon atoms get fixed. As a result, several alkenes can exhibit geometrical isomerism.

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128.

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

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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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