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Difficulty: EasyFunctional Groups, Homologous Series, and IUPAC Nomenclature

What is the correct IUPAC name for the organic compound with the condensed structural formula CH3−CH2−CH(CH2CH3)−CH3\text{CH}_3-\text{CH}_2-\text{CH}(\text{CH}_2\text{CH}_3)-\text{CH}_3?

  1. 3-methylpentaneAnswer
  2. B
    2-ethylbutane
  3. C
    3-ethylbutane
  4. D
    2-methylpentane

Answer

3-methylpentane
The correct IUPAC name is determined by finding the longest continuous chain of carbon atoms. Expanding the condensed formula CH3−CH2−CH(CH2CH3)−CH3\text{CH}_3-\text{CH}_2-\text{CH}(\text{CH}_2\text{CH}_3)-\text{CH}_3 shows that the longest continuous chain contains 5 carbons (pentane). The remaining branch is a methyl group at carbon-3, making the systematic name 3-methylpentane.

Step-by-Step Solution

1
Identify the longest continuous carbon chain in the structure.
Expanding CH3−CH2−CH(CH2CH3)−CH3\text{CH}_3-\text{CH}_2-\text{CH}(\text{CH}_2\text{CH}_3)-\text{CH}_3 shows a continuous chain of 5 carbon atoms (pentane).
IUPAC nomenclature rules dictate that the parent chain must be the longest continuous chain of carbon atoms.
2
Identify substituents and number the parent chain.
A methyl group (−CH3-\text{CH}_3) is attached at carbon-3.
Numbering the 5-carbon chain from either end places the substituent at position 3.
3
Combine the substituent locant, substituent name, and parent alkane name.
The correct IUPAC name is 3-methylpentane.
Combining the locant (3), substituent (methyl), and parent (pentane) yields 3-methylpentane.

Key Concept

Identification of the longest continuous carbon chain in IUPAC organic nomenclature
Estimated Time:45s
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Topics

Functional Groups, Homologous Series, and IUPAC Nomenclature

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