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#proton NMR

3 public questions tagged with this topic.

NMRSpectroscopy

The coupling constant in ¹³CH₃Cl proton NMR is:

One-bond carbon-proton coupling in 13CH3Cl arises from Fermi contact interaction between directly bonded magnetic nuclei, magnitude proportional to gyromagnetic ratios and s-character, typically 125 to 160 Hz for sp3 carbon, much larger than vicinal proton-proton couplings near 7 Hz. Observed value around 140 Hz reflects strong interaction in chlorinated alkane, producing widely spaced doublet satellites in proton spectrum when decoupling absent. This large constant enables polarization transfer in INEPT and DEPT experiments, underpins HSQC sensitivity enhancement, and is exploited for carbon editing in metabolomics and protein-labeled samples.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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NMRSpectroscopy

In ¹³CH₃Cl, how many peaks in ¹H NMR?

Enriching methyl chloride with 100 percent carbon-13 replaces spin-zero 12C with magnetic I equals one-half nucleus, active in NMR. Protons directly bonded to 13C experience heteronuclear one-bond coupling 1JCH, splitting proton resonance into doublet following n+1 rule where n equals one magnetic neighbor. Remaining 12CH3Cl molecules still show central singlet. This pair of satellites flanking main peak demonstrates heteronuclear splitting, foundational for HSQC and HMQC editing that separates labeled from unlabeled pools, crucial for isotope tracing in metabolism and protein backbone assignments.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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NMRSpectroscopy

What is the nuclear spin quantum number (I) for ¹H?

Protium nucleus contains one proton with odd mass number, producing intrinsic spin quantum number one-half. Quantum spin generates a magnetic moment with two Zeeman orientations, +1/2 and -1/2, in external magnetic field, permitting resonant radiofrequency absorption central to NMR. Nuclei with even protons and neutrons possess zero spin, while odd-odd combinations yield integer spins. Half-integer spin confers high gyromagnetic ratio and abundant sensitivity, making hydrogen indispensable for protein, metabolite, water, and lipid detection in biological NMR experiments and medical MRI imaging.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details