Concept: Geometrical isomerism (also known as cis-trans isomerism) is a type of stereoisomerism that can occur in molecules with restricted rotation around a bond, typically a carbon-carbon double bond ( ) or in cyclic compounds.
For geometrical isomerism around a double bond, two conditions must be met:
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(W) There must be restricted rotation around the bond (which is inherent to double bonds).
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(X) Each carbon atom of the double bond must be attached to two different atoms or groups. Step 1: Analyze the structures of the given compounds % Option
(Y) (1) Butanol-2 (2-Butanol): . This is an alcohol and does not have a double bond relevant for geometrical isomerism in its main chain. (It has a chiral center and can exhibit optical isomerism, but not geometrical isomerism in the typical alkene sense).
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(Z) (2) Butene-1 (1-Butene): . Let's look at the carbons of the double bond ( ): % Option
([) is attached to two Hydrogen atoms (H, H). Since these two groups are identical, geometrical isomerism is not possible around this bond.
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(\) is attached to a Hydrogen atom (H) and an Ethyl group ( ). Since has two identical groups (H, H), 1-Butene does not exhibit geometrical isomerism.
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(]) (3) Butene-2 (2-Butene): . Let's look at the carbons of the double bond ( ): % Option
(^) is attached to a Hydrogen atom (H) and a Methyl group ( ). These are different.
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(_) is attached to a Hydrogen atom (H) and a Methyl group ( ). These are different. Since both and are each attached to two different groups, 2-Butene can exhibit geometrical isomerism (cis-2-butene and trans-2-butene). % Option
(`) {cis}-2-Butene: Methyl groups are on the same side of the double bond.
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(a) {trans}-2-Butene: Methyl groups are on opposite sides of the double bond. % Option
(b) (4) Butyne-1 (1-Butyne): . This molecule has a carbon-carbon triple bond ( ). Triple bonds are linear around the alkyne carbons and do not exhibit geometrical isomerism of the cis-trans type. Step 2: Identifying the compound exhibiting geometrical isomerism
Based on the analysis, Butene-2 (2-Butene) meets the criteria for geometrical isomerism.