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Difficulty: MediumStructural Isomerism and Stereoisomerism

Which of the following structural isomers of hexane, C6H14C_6H_{14}, contains exactly one tertiary carbon atom?

  1. 2-MethylpentaneAnswer
  2. B
    2,3-Dimethylbutane
  3. C
    2,2-Dimethylbutane
  4. D
    Hexane

Answer

2-Methylpentane contains exactly one tertiary carbon atom.
A tertiary carbon atom is defined as a carbon atom bonded to three other carbon atoms. In 2-methylpentane, the carbon atom at position 2 is bonded to C-1, C-3, and the branch methyl group, making it the only tertiary carbon atom in the molecule.

Step-by-Step Solution

1
Define a tertiary carbon atom
A tertiary carbon atom (3∘3^\circ) is directly bonded to three other carbon atoms.
Carbon classification depends on the number of attached alkyl/carbon groups.
2
Analyze the carbon skeleton of 2-Methylpentane
In CH3−CH(CH3)−CH2−CH2−CH3CH_3-CH(CH_3)-CH_2-CH_2-CH_3, C-2 is bonded to C-1, C-3, and the methyl group.
This structural arrangement yields exactly one tertiary carbon atom.
3
Evaluate the remaining options
2,3-Dimethylbutane has two tertiary carbons, 2,2-Dimethylbutane has one quaternary carbon (zero tertiary), and unbranched hexane has zero tertiary carbons.
Only 2-Methylpentane satisfies the condition of having exactly one tertiary carbon atom.

Key Concept

Classification of carbon atoms in structural isomers
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Topics

Structural Isomerism and Stereoisomerism

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