MCAT Organic Chemistry Question 43: Answer and Explanation

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Question: 43

13. A resonance structure describes:

I. the hybrid of all possible structures that contribute to electron distribution

II. a potential arrangement of electrons in a molecule.

III. the single form that the molecule most often takes.

  • A. I only
  • B. II only
  • C. I and II only
  • D. I, II, and III

Correct Answer: B

Explanation:

A resonance structure describes an arrangement of electrons in a molecule. Different resonance structures can be derived by moving electrons in unhybridized p-orbitals throughout a molecule containing conjugated bonds. In molecules that contain multiple resonance structures, some are usually more stable than others; however, each resonance structure is not necessarily the most common form a molecule takes, eliminating statement III. Statement I has reversed the terminology for resonance structures: the electron density in a molecule is the weighted average of all possible resonance structures, not the other way around.

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