MCAT Organic Chemistry Question 155: Answer and Explanation

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Question: 155

5. The isotope ¹²C is not useful for NMR because:

A. it is not abundant in nature.
B. its resonances are not sensitive to the presence of neighboring atoms.
C. it has no magnetic moment.
D. the signal-to-noise ratio in the spectrum is too low.

Correct Answer: C

Explanation:

This isotope has no magnetic moment and will therefore not exhibit resonance with an applied magnetic field. Nuclei with odd mass numbers (¹H, ¹¹B, ¹³C, ¹⁵N, ¹⁹F, and so on) or those with an even mass number but an odd atomic number (²H, ¹⁰B) will have a nonzero magnetic moment.

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