Question

Why is the carbon-13 isotope used for carbon NMR?

A. It is the only isotope of carbon that is found in living tissue.

B. Other isotopes of carbon are radioactive and not useful for precise measurements.

C. Other isotopes of carbon are much more difficult to detect in an NMR machine.

D. Carbon-13 is radioactive and can be easily detected with a scintillation counter.

Answer 1

. Carbon-13 is radioactive and can be easily detected with a scintillation counter.

Other isotopes of carbon are not detect in an NMR machine.

The 12C isotope of carbon - which accounts for up about 99% of the carbons in organic molecules - does not have a nuclear magnetic moment, and thus is NMR-inactive. Fortunately for organic chemists, however, the 13C isotope, which accounts for most of the remaining 1% of carbon atoms in nature, has a magnetic moment just like protons. Most of what we have learned about 1H-NMR spectroscopy also applies to 13C-NMR, although there are several important differences.

Since organic compounds are largely based on carbon, ¹³C NMR spectroscopy is a pretty important tool for studying organic compounds. The ¹³C isotope is the only isotope of carbon that is "NMR-active"; ¹²C and ¹⁴C atoms do not absorb radio waves in a magnetic field.