MCAT Organic Chemistry Question 6: Answer and Explanation

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Question: 6

6. Which of the two possibilities below correctly numbers the carbon backbone of this molecule?

  • A. Numbering Scheme 1
  • B. Numbering Scheme 2
  • C. Numbering Schemes 1 and 2 are equivalent and correct
  • D. Numbering Schemes 1 and 2 are equivalent and incorrect.

Correct Answer: A

Explanation:

This molecule is 3-ethyl-4-methylhexane, not 2,3-diethylpentane. When naming alkanes, one must locate the longest carbon chain (6 carbons, rather than 5 carbons), and the numbering system should give the alkyl groups the lowest possible numbers.

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