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.