NMR Fundamentals—Do All Hydrogen Nuclei Resonate the Same? In proton nuclear magnetic resonance (¹H NMR) spectroscopy, which statement best describes how hydrogen nuclei resonate?

Introduction / Context:
¹H NMR exploits the fact that nuclear spins experience slightly different local magnetic fields due to surrounding electrons. These differences shift their resonance frequencies, producing the chemical shift pattern that helps chemists identify functional groups and molecular environments.

Given Data / Assumptions:

• Constant external magnetic field B0 is applied.
• Hydrogen nuclei in different chemical environments have varying electron densities.
• Shielding/deshielding effects shift resonance frequencies.

Concept / Approach:
Electrons circulate in the applied field and generate local fields that oppose or augment B0. A more shielded proton experiences a smaller effective field and resonates at a higher field (upfield, lower ppm), while a deshielded proton experiences a larger effective field, resonating downfield (higher ppm). Therefore, hydrogen nuclei do not all resonate identically; their frequencies depend on chemical environment.

Step-by-Step Solution:

Verification / Alternative check:
Experimental spectra of ethanol show distinct signals for CH3, CH2, and OH protons, directly evidencing environment-dependent resonance.

Why Other Options Are Wrong:

• (a) Incorrect—chemical shift diversity is the basis of NMR structure elucidation.
• (c) Not all hydrogens are C–H; O–H, N–H, S–H exist.
• (d) ¹H and ¹³C have very different gyromagnetic ratios and resonance frequencies.
• (e) Shielding is central to NMR; resonance absolutely depends on it.

Common Pitfalls:
Confusing ppm scale with absolute frequency; ppm normalizes across instrument field strengths.

Final Answer:
Hydrogen nuclei resonate at different frequencies depending on their electronic/chemical environment