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Difficulty: EasyStructural Isomerism and Stereoisomerism

But-1-ene and but-2-ene share the molecular formula C4H8C_4H_8 but differ in the location of their carbon-carbon double bond. Which type of structural isomerism do these two compounds exhibit?

  1. A
    Chain isomerism
  2. Positional isomerismAnswer
  3. C
    Functional group isomerism
  4. D
    Geometric isomerism

Answer

Positional isomerism
Positional isomerism occurs when compounds with the same carbon skeleton and the same functional group differ only in the location of that functional group on the chain. But-1-ene and but-2-ene both have a straight four-carbon chain, but the double bond starts at position 1 and position 2 respectively.

Step-by-Step Solution

1
Examine the structures of both molecules.
Both but-1-ene (CH2=CH−CH2−CH3CH_2=CH-CH_2-CH_3) and but-2-ene (CH3−CH=CH−CH3CH_3-CH=CH-CH_3) have a straight four-carbon chain and an alkene functional group.
Comparing carbon chain structure and functional group identity helps determine isomer type.
2
Identify the structural difference between the two molecules.
The double bond is located between carbon-1 and carbon-2 in but-1-ene, but between carbon-2 and carbon-3 in but-2-ene.
Compounds with the same carbon framework that differ only in the location of the functional group are classified as positional isomers.

Key Concept

Positional Isomerism in Alkenes
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Topics

Structural Isomerism and Stereoisomerism

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