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Difficulty: EasyFunctional Groups, Homologous Series, and IUPAC Nomenclature

What is the correct IUPAC name for the branched alkane with the structural formula CH3−CH(CH3)−CH2−CH3\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3?

  1. 2-methylbutaneAnswer
  2. B
    3-methylbutane
  3. C
    2-ethylpropane
  4. D
    pentane

Answer

The correct IUPAC name for the compound is 2-methylbutane.
The longest continuous carbon chain consists of 4 carbon atoms (butane). Numbering from the end closest to the branch assigns the methyl group to position 2, giving the correct IUPAC name 2-methylbutane.

Step-by-Step Solution

1
Identify the longest continuous carbon chain.
The longest chain has 4 carbon atoms, which corresponds to the parent alkane butane.
IUPAC rules mandate that the parent structure is named according to the longest continuous chain of carbon atoms.
2
Number the parent carbon chain to give substituents the lowest locant numbers.
Numbering from left to right assigns the methyl group to carbon-2 (CC-2), whereas right to left gives carbon-3 (CC-3). Thus, left-to-right numbering is correct.
Substituents must receive the lowest possible numerical locants.
3
Assemble the complete IUPAC name.
The substituent prefix '2-methyl' combined with the parent 'butane' gives 2-methylbutane.
The full name consists of the substituent position, substituent name, and parent alkane name.

Key Concept

IUPAC rules for branched alkanes: identifying the longest continuous carbon chain and assigning the lowest position number to alkyl substituents.
Estimated Time:45s
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Topics

Functional Groups, Homologous Series, and IUPAC Nomenclature

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