Principles of Proton (1H) Nuclear Magnetic Resonance spectroscopy MCQs With Answer

Proton (1H) Nuclear Magnetic Resonance (NMR) spectroscopy is a core analytical tool for B. Pharm students, enabling precise structural elucidation, identification of functional groups, and assessment of purity in drug molecules. This introduction explains essential concepts—chemical shift, shielding and deshielding, spin-spin (J) coupling, multiplicity, integration, and the role of reference standards such as TMS—paired with practical points like deuterated solvents, sample preparation, exchangeable protons (OH/NH), peak broadening, and anisotropic effects (aromatic, alkene, carbonyl). Mastery of these principles improves interpretation of spectra, prediction of splitting patterns, and determination of molecular connectivity. Keywords: Proton NMR, 1H NMR, chemical shift, coupling constant, integration, TMS, deuterated solvent, spin-spin coupling. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which nucleus is observed in Proton NMR spectroscopy commonly used in pharmaceutical analysis?

• 12C
• 1H
• 13C
• 31P

Correct Answer: 1H

Q2. What is the standard chemical shift reference used in routine 1H NMR spectra?

• Chloroform (CHCl3)
• Water (H2O)
• Tetramethylsilane (TMS)
• Acetone

Correct Answer: Tetramethylsilane (TMS)

Q3. Which effect causes a proton’s signal to appear downfield (higher ppm) relative to another proton?

• Increased shielding
• Deshielding by electronegative atoms or anisotropy
• Being in a more electron-rich environment
• Stronger magnetic field only

Correct Answer: Deshielding by electronegative atoms or anisotropy

Q4. The integration of a 1H NMR signal provides information about:

• The chemical shift value
• The number of chemically equivalent protons
• The coupling constant
• The solvent used

Correct Answer: The number of chemically equivalent protons

Q5. According to the n+1 rule, a proton with two equivalent neighboring protons will appear as:

• A singlet
• A doublet
• A triplet
• A quartet

Correct Answer: A triplet

Q6. Which typical chemical shift range corresponds to aromatic protons in 1H NMR?

• 0.5–2.0 ppm
• 2.0–4.5 ppm
• 6.0–8.5 ppm
• 9.0–12.0 ppm

Correct Answer: 6.0–8.5 ppm

Q7. What is the typical magnitude of a vicinal (3J) H–H coupling constant in simple aliphatic systems?

• 0–1 Hz
• ~7 Hz
• ~50 Hz
• 100–200 Hz

Correct Answer: ~7 Hz

Q8. Which solvent is most commonly used as a deuterated NMR solvent for organic compounds?

• H2O
• CDCl3 (deuterated chloroform)
• CH3OH (protic methanol)
• Acetonitrile (non-deuterated)

Correct Answer: CDCl3 (deuterated chloroform)

Q9. Exchangeable protons such as OH or NH often show which behavior in 1H NMR?

• Sharp, highly split multiplets
• Disappear or broaden upon addition of D2O
• Always appear at 0 ppm
• Show strong long-range coupling with aromatic protons

Correct Answer: Disappear or broaden upon addition of D2O

Q10. What causes second-order (complex) splitting patterns in 1H NMR?

• Very large chemical shift differences between coupled protons
• Solvent impurities only
• Similar chemical shifts and comparable coupling constants between interacting protons
• Absence of magnetic field homogeneity

Correct Answer: Similar chemical shifts and comparable coupling constants between interacting protons

Q11. A methyl group adjacent to an electronegative atom (e.g., OCH3) will be shifted approximately to which region?

• 0.0–0.5 ppm
• 0.5–1.5 ppm
• 3.0–4.0 ppm
• 6.0–8.0 ppm

Correct Answer: 3.0–4.0 ppm

Q12. Which statement about TMS is correct?

• TMS is used because it is paramagnetic
• TMS gives multiple signals across the spectrum
• TMS is chemically inert and gives a sharp signal at 0 ppm
• TMS is rarely used in organic NMR

Correct Answer: TMS is chemically inert and gives a sharp signal at 0 ppm

Q13. In aromatic substitution analysis, ortho-coupling constants (3J) are typically around:

• 0–1 Hz
• 2–4 Hz
• 6–9 Hz
• 15–20 Hz

Correct Answer: 6–9 Hz

Q14. Which technique provides correlations between coupled protons and helps assign overlapping 1H signals?

• IR spectroscopy
• 1D 13C NMR only
• COSY (2D homonuclear correlation)
• Mass spectrometry

Correct Answer: COSY (2D homonuclear correlation)

Q15. A quartet at ~1.2 ppm (integral 3H) and a triplet at ~3.6 ppm (integral 2H) most likely indicate which fragment?

• Isopropyl group
• Ethyl group (CH3CH2X)
• Tert-butyl group
• Aromatic CH3

Correct Answer: Ethyl group (CH3CH2X)

Q16. Which factor does NOT significantly affect chemical shift in 1H NMR?

• Electronegativity of neighboring atoms
• Magnetic anisotropy from double bonds or aromatic rings
• Sample temperature within a moderate range
• Detector brand of the NMR instrument

Correct Answer: Detector brand of the NMR instrument

Q17. Long-range coupling (4J or more) usually has what typical coupling constant magnitude?

• ~10–20 Hz
• ~0–3 Hz
• ~30–50 Hz
• ~100 Hz

Correct Answer: ~0–3 Hz

Q18. Proton signals that appear as multiplets with complex patterns often indicate:

• Fully equivalent protons with no neighbors
• Multiple non-equivalent couplings with several neighboring protons
• Presence of only deuterium atoms
• A pure singlet from isolated protons

Correct Answer: Multiple non-equivalent couplings with several neighboring protons

Q19. Why are deuterated solvents used in 1H NMR?

• They increase the number of proton signals
• They provide a lock signal and avoid large solvent proton peaks
• They are cheaper than non-deuterated solvents
• They cause faster relaxation of sample protons

Correct Answer: They provide a lock signal and avoid large solvent proton peaks

Q20. In a molecule with two chemically equivalent protons, how many distinct signals do those protons produce in a simple spectrum?

• Two distinct signals
• No signal
• One signal
• Four signals

Correct Answer: One signal

Q21. What information does the coupling constant (J) primarily give?

• Number of protons in the molecule
• Distance in angstroms between nuclei
• Type of scalar coupling and dihedral angle relationship between coupled nuclei
• Exact chemical formula

Correct Answer: Type of scalar coupling and dihedral angle relationship between coupled nuclei

Q22. Which protons typically appear downfield near 9–10 ppm in 1H NMR?

• Aromatic methyl protons
• Aldehyde protons
• Allylic protons

Correct Answer: Aldehyde protons

Q23. In presence of rapid chemical exchange (e.g., acidic OH in protic solvent), what happens to the OH signal?

• It splits into many fine lines
• It shows very large J coupling with all protons
• It often appears broadened or disappears
• It shifts to exactly 0 ppm

Correct Answer: It often appears broadened or disappears

Q24. Which of the following best describes shielded protons?

• Protons near electronegative atoms showing high ppm
• Protons in an electron-rich environment appearing upfield (lower ppm)
• Protons that always couple strongly with fluorine
• Protons that give no NMR signal

Correct Answer: Protons in an electron-rich environment appearing upfield (lower ppm)

Q25. A multiplet described as a doublet of doublets indicates:

• One proton coupling equally to three identical neighbors
• Two different coupling constants to two non-equivalent neighboring protons
• A pure singlet broadened by solvent
• No couplings present

Correct Answer: Two different coupling constants to two non-equivalent neighboring protons

Q26. Which NMR experimental practice reduces peak broadening due to field inhomogeneity?

• Skipping shimming
• Proper shimming and locking
• Using non-deuterated solvent
• Increasing sample impurities

Correct Answer: Proper shimming and locking

Q27. In interpreting a 1H NMR spectrum, the total integral value corresponds to:

• Molecular weight directly
• Relative number of protons represented by each signal
• Absolute concentration in mol/L without calibration
• The number of carbon atoms

Correct Answer: Relative number of protons represented by each signal

Q28. Which coupling is observed between 1H and 19F or 31P nuclei?

• Heteronuclear scalar coupling
• Only dipolar coupling
• No coupling is possible
• Only through-space NOE coupling

Correct Answer: Heteronuclear scalar coupling

Q29. How can one confirm that a peak at ~7.26 ppm is from residual CHCl3 in CDCl3?

• By running IR spectroscopy
• By checking known residual solvent peaks and the deuterated solvent used
• By heating the sample to 200 °C
• By adding more TMS

Correct Answer: By checking known residual solvent peaks and the deuterated solvent used

Q30. The Karplus relationship links which two NMR parameters?

• Chemical shift and integration
• Coupling constant (3J) and dihedral angle between vicinal protons
• Solvent polarity and peak multiplicity
• Sample concentration and chemical shift

Correct Answer: Coupling constant (3J) and dihedral angle between vicinal protons

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com