MCAT General Chemistry Question 255: Answer and Explanation

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Question: 255

4. All of the following molecules will display absorption peaks in an IR spectrum EXCEPT

A. HClO₄
B. SO₃
C. CO
D. O₂

Correct Answer: D

Explanation:

D The passage states that only those normal modes of vibration that produce a change in the dipole moment of a molecule will absorb IR light. Since O₂ has no dipole, it will not have any peaks in an IR spectrum. Note that while the molecule SO₃ as a whole has no dipole, its individual bonds do have detectable dipoles.

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