Question

Question: Label each statement as True or False.

a. When a nucleus is strongly shielded, the effective field is larger than the applied field and the absorption shifts downfield.

b. When a nucleus is strongly shielded, the effective field is smaller than the applied field and the absorption is shifted upfield.

c. A nucleus that is strongly deshielded requires a lower field strength for resonance.

d. A nucleus that is strongly shielded absorbs at a larger δ value.

Short answer

1. False
2. False
3. False
4. False

Step-by-step solution

NMR spectroscopy

The chemical shift of the proton is related to its surrounding groups. For example, an electronegative atom affects the chemical shift of the proton; it brings the proton downshield.

Explanation

a.

Consider that the nucleus is strongly shielded and the induced magnetic field is larger than the applied field. Thus, the resultant magnetic field would be less than the applied filed.

Due to this, the proton has less value of chemical shift or absorbs at a lower value of delta, which means it will be upfield. Therefore, the given statement is false.

b.

Consider that the nucleus is strongly deshielded and the induced magnetic field has lower value than the applied field. Thus, the resultant magnetic field would have larger value than the applied filed.

Due to this, proton has more value of chemical shift or absorbs at a larger value of delta, which means it will be downfield. Therefore, the given statement is false.

c.

Deshielded nucleus requires high filed strength for the resonance. Thus, the given statement is false.

d.

Deshielded nucleus requires or absorbs at a large value of delta.. Thus, the given statement is false.