H NMR Spectroscopy Practice Questions PDF

1. What property of hydrogen nuclei is exploited in 1H NMR spectroscopy? * A) Their mass * B) Their spin * C) Their charge * D) Their ability to form hydrogen bonds 2. What does the number of signals in a 1H NMR spectrum indicate? * A) The number of hydrogen atoms in the molecule. * B) The number o...

1. What property of hydrogen nuclei is exploited in 1H NMR spectroscopy? * A) Their mass * B) Their spin * C) Their charge * D) Their ability to form hydrogen bonds 2. What does the number of signals in a 1H NMR spectrum indicate? * A) The number of hydrogen atoms in the molecule. * B) The number of different chemical environments of hydrogen atoms. * C) The number of carbon atoms in the molecule. * D) The molecular mass of the compound. 3. What is meant by the term "chemical shift" in 1H NMR? * A) The position of a signal along the x-axis, relative to a standard. * B) The intensity of a signal. * C) The splitting pattern of a signal. * D) The number of signals in the spectrum. 4. What is the standard reference compound used in 1H NMR spectroscopy? * A) Chloroform * B) Water * C) Tetramethylsilane (TMS) * D) Ethanol 5. Why is TMS a suitable reference compound? * A) It is very reactive. * B) It produces multiple signals. * C) It is inert, volatile, and has 12 equivalent protons, producing a single, strong signal. * D) It is expensive. 6. What information does the integration trace (or area under the peak) provide in a 1H NMR spectrum? * A) The chemical shift of the protons. * B) The relative number of protons in each environment. * C) The splitting pattern of the protons. * D) The identity of the functional groups present. 7. What causes spin-spin splitting in a 1H NMR spectrum? * A) The interaction of hydrogen nuclei with the applied magnetic eld. * B) The interaction of hydrogen nuclei with adjacent, non-equivalent hydrogen nuclei. * C) The interaction of hydrogen nuclei with the solvent. * D) The presence of electronegative atoms. 8. What is the n+1 rule used to predict in 1H NMR? * A) The chemical shift * B) The integration value * C) The splitting pattern (number of peaks in a signal) * D) The number of signals 9. A proton environment has two neighboring, non-equivalent protons. What will its splitting pattern be? * A) Singlet * B) Doublet * C) Triplet * D) Quartet 10. A proton environment has three neighboring, non-equivalent protons. What will its splitting pattern be? * A) Singlet * B) Doublet * C) Triplet * D) Quartet 12. Which of the following solvents is commonly used in 1H NMR because it does not contain protons? * A) H2O * B) CDCl3 * C) CH3OH * D) C2H5OH Answers and Explanations: fi  1. B - The spin of the hydrogen nucleus (proton) creates a tiny magnetic eld. 2. B - Each unique chemical environment of H atoms produces a separate signal. 3. A - Chemical shift is the position of the signal, measured in ppm, relative to TMS. 4. C 5. C - TMS is inert, volatile, and its 12 equivalent H's produce a single, strong, up eld signal. 6. B - The area under the peak is proportional to the number of H atoms in that environment. 7. B - Splitting is caused by the magnetic in uence of *non-equivalent* protons on adjacent atoms. 8. C - n+1 rule: If a proton has 'n' non-equivalent neighboring protons, its signal will be split into n+1 peaks. 9. C - 2 + 1 = 3 peaks (triplet) 10. D - 3+1 = 4 peaks 11. B- The -OH proton signal is often a singlet, and can vary. Rapid exchange with other OH groups/acidic protons often averages out any coupling. 12. B - CDCl3 (deuterated chloroform) has no protons to interfere with the sample's spectrum. 13. A - D replaces H in -OH and -NH groups. Deuterium doesn't show up in the 1H NMR spectrum. 14. A 15. D - Aldehyde protons are highly deshielded and appear at very low eld (high ppm). fi fi fi fl