Question

In 1H NMR spectrum of the given molecule, the correct order of chemical shifts of the labelled protons (H$^X$, H$^Y$, H$^Z$) is 

• A. H$^Z$>H$^X$>H$^Y$
• B. H$^Z$>H$^Y$>H$^X$
• C. H$^X$>H$^Y$>H$^Z$
• D. H$^Y$>H$^X$>H$^Z$

Hint:

In 1H NMR, protons attached to electronegative groups or groups that withdraw electron density will appear at higher chemical shifts.

Answer 1

The Correct Option is D

Step 1: Analyze the chemical shifts.
In 1H NMR, the chemical shift depends on the electronic environment of the protons. Protons attached to electron-withdrawing groups such as electronegative atoms (e.g., oxygen, chlorine) will resonate at higher chemical shifts. Protons in more shielded environments will resonate at lower chemical shifts.
Step 2: Analyzing the positions of the protons.
- H$^Z$: The proton near an electronegative group (e.g., a halogen) will experience a deshielding effect, leading to a higher chemical shift. - H$^Y$: This proton is likely attached to a carbon adjacent to an electron-withdrawing group, so it will resonate at a moderate chemical shift. - H$^X$: This proton will be the most shielded and will resonate at the lowest chemical shift.
Step 3: Conclusion.
Thus, the correct order of chemical shifts is H$^Z$>H$^Y$>H$^X$, which corresponds to option (B).