MCAT Organic Chemistry Question 61: Answer and Explanation

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Question: 61

1. Alcohols have higher boiling points than their analogous hydrocarbons because:

  • A. the oxygen atoms in alcohols have shorter bond lengths.
  • B. hydrogen bonding is present in alcohols.
  • C. alcohols are more acidic than their analogous hydrocarbons.
  • D. alcohols can be oxidized to ketones.

Correct Answer: B

Explanation:

Alcohols have higher boiling points than their analogous hydrocarbons as a result of their polarized O–H bonds, in which oxygen is partially negative and hydrogen is partially positive. This enables the oxygen atoms of other alcohol molecules to be attracted to the hydrogen, forming a hydrogen bond. Heat is required to break these hydrogen bonds, thereby increasing the boiling point. The analogous hydrocarbons do not form hydrogen bonds and, therefore, vaporize at lower temperatures. Choice (A) is irrelevant; oxygen’s bond length is not a factor in determining a substance’s boiling point. Choices (C) and (D) are true statements, but are also irrelevant to boiling point determination.

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