Q.48 Which of the following nucleus/nuclei is/are NMR active?
(A) 1H
(B) 13C
(C) 16O
(D) 32S
Which Nuclei Are NMR Active? 1H, 13C, 16O, and 32S Explained
Nuclei are NMR active if they possess a non-zero nuclear spin quantum number (I ≠ 0), allowing them to interact with an external magnetic field in Nuclear Magnetic Resonance spectroscopy. Among the options, (A) ¹H and (B) ¹³C are NMR active, while (C) ¹⁶O and (D) ³²S are not. This principle determines their utility in structural analysis for biological and chemical research.
Nuclear Spin Basics
A nucleus has non-zero spin (I ≠ 0) if it contains an odd number of protons or neutrons, enabling energy level splitting in a magnetic field for NMR detection. Nuclei with even numbers of both protons (Z) and neutrons (N) have I = 0 and are NMR inactive, producing no signal. This rule applies across isotopes commonly studied in molecular biology and plant sciences.
Option Analysis
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(A) ¹H (Proton): Z=1 (odd), N=0 (even); I = 1/2. Highly sensitive and routinely used in ¹H NMR for identifying hydrogen environments in biomolecules.
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(B) ¹³C: Z=6 (even), N=7 (odd); I = 1/2. Essential for ¹³C NMR in organic structure elucidation, despite lower natural abundance (~1%).
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(C) ¹⁶O: Z=8 (even), N=8 (even); I = 0. NMR inactive, so no ¹⁶O signals appear in spectra despite oxygen’s prevalence in biological molecules.
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(D) ³²S: Z=16 (even), N=16 (even); I = 0. NMR inactive; sulfur studies require other isotopes like ³³S (I=3/2).
Applications in Research
¹H and ¹³C NMR drive advances in genetics and biochemistry, revealing protein structures and metabolic pathways. Inactive nuclei like ¹⁶O and ³²S limit direct observation but allow focus on active isotopes for precise analysis. Researchers in Jaipur’s biotech hubs leverage these for plant physiology and enzyme kinetics studies.
