Question

Consider the following statements regarding NMR spectroscopy. Determine whether each each statement is true or false.

Spin-spin splitting can occur over many bond lengths in a molecule.

NMR spectroscopy requires a nucleus having non-zero electron spin.

Shielding occurs when electrons near a proton are induced to circulate by the applied field. This electron field opposes the applied field.

A typical value for the chemical shift of aromatic protons is 7.5.

Answer 1

•Spin-spin splitting can occur over many bond lengths in a molecule. -> False ( spin-spin splitting is maximum over 2 bonds)

•NMR spectroscopy requires a nucleus having non-zero electron spin. -> True

• Shielding occurs when electrons near a proton are induced to circulate by the applied field. This electron field opposes the applied field. -> True [Shielding:
The higher the electron density around the nucleus, the higher the opposing magnetic field to B0 from the electrons, the greater the shielding. Because the proton experiences lower external magnetic field, it needs a lower frequency to achieve resonance, and therefore, the chemical shift shifts upfield (lower ppms) .]

• A typical value for the chemical shift of aromatic protons is 7.5. -> True (Aromatic hydrogen atoms have a chemical shift value of about 7.0-9.0 ppm )