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Difficulty: MediumStructural Isomerism and Stereoisomerism

How many acyclic structural isomers exist for the haloalkane with the molecular formula C4H9ClC_4H_9Cl?

  1. A
    2
  2. B
    3
  3. 4Answer
  4. D
    5

Answer

There are 4 acyclic structural isomers for C4H9ClC_4H_9Cl.
The molecular formula C4H9ClC_4H_9Cl allows for both chain isomerism (butane vs. methylpropane carbon backbones) and positional isomerism (placement of the chlorine atom). This results in four distinct IUPAC structures: 1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, and 2-chloro-2-methylpropane.

Step-by-Step Solution

1
Identify structural isomers based on the straight-chain butyl skeleton (CH3−CH2−CH2−CH3CH_3-CH_2-CH_2-CH_3).
Two positional isomers are obtained: 1-chlorobutane (CH3CH2CH2CH2ClCH_3CH_2CH_2CH_2Cl) and 2-chlorobutane (CH3CH2CH(Cl)CH3CH_3CH_2CH(Cl)CH_3).
Varying the position of the chlorine atom on a four-carbon unbranched chain yields two distinct structures.
2
Identify structural isomers based on the branched methylpropane skeleton ((CH3)2CH−CH3(CH_3)_2CH-CH_3).
Two chain/positional isomers are obtained: 1-chloro-2-methylpropane ((CH3)2CHCH2Cl(CH_3)_2CHCH_2Cl) and 2-chloro-2-methylpropane ((CH3)3CCl(CH_3)_3CCl).
Attaching the chlorine atom to a primary carbon versus the tertiary carbon of the methylpropane backbone yields two additional unique isomers.
3
Sum the distinct structural isomers found.
Total number of isomers = 2+2=42 + 2 = 4.
All possible constitutional connectivities for C4H9ClC_4H_9Cl have been evaluated without double counting.

Key Concept

Structural Isomerism in Haloalkanes
Estimated Time:1m 15s
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Topics

Structural Isomerism and Stereoisomerism

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