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#1H NMR

3 public questions tagged with this topic.

NMRSpectroscopy

What is the chemical shift range for ¹H NMR?

Proton NMR window spans approximately zero to twelve ppm because hydrogen experiences limited shielding variation: shielded alkanes resonate 0.8 to 1.5 ppm, electron-withdrawing alpha carbons 3 to 5 ppm, aromatic and amide protons 6 to 10 ppm, aldehydes near 9 to 10 ppm. Carbon-13 range extends 0 to 220 ppm due to larger paramagnetic shielding effects. Knowing proton window helps students rapidly categorize signals in protein hydrolysates, urine metabolomics, and nucleic acid imino regions, distinguishing aliphatic core from deshielded hydrogen-bonded protons in folded structures.

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 ¹H NMR, a proton with 2 equivalent neighbors shows:

When a proton couples to n equivalent neighbors of spin one-half, first-order theory predicts n+1 lines with intensity ratios given by binomial coefficients from Pascal's triangle. Two equivalent protons create four spin combinations: up-up, up-down, down-up, down-down, merging middle two to produce triplet with 1:2:1 intensities. Observing triplet therefore indicates adjacent methylene group, such as CH2 in ethanol or glutamate side chain. Coupling constant remains identical for both partners, allowing cross-validation of assignments in complex biomolecular spectra and metabolic pathway analy

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 causes splitting in ¹H NMR spectrum?

Splitting arises from indirect spin-spin coupling transmitted via bonding electrons, termed J-coupling or scalar coupling. Neighboring magnetic nuclei perturb energy levels through Fermi contact interaction, creating multiple transition frequencies. Equivalent neighbors split signal into n+1 components, with separation equal to coupling constant in hertz. This through-bond mechanism, not through-space, carries stereochemical information. In peptides, three-bond HN-Hα coupling reports phi angle via Karplus relationship, crucial for secondary structure determination, confirming alpha helix or be

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