Spectral methods for structure determination: IR, UV‑Vis, 1H and 13C NMR and mass spectrometry - Question Bank
1. Which type of electronic transition typically requires the least energy and is observed at the longest wavelengths in UV-Vis spectroscopy for molecules with π systems?
2. What does the term 'spin-spin coupling constant' (J) in NMR represent?
3. A broad absorption band in the IR spectrum between 2500-3300 cm⁻¹ is characteristic of which functional group?
4. Which method is commonly used in MS to determine the elemental composition of ions based on precise mass measurements?
5. In ¹H NMR, a downfield shift (higher ppm value) of a proton signal generally indicates that the proton is:
6. The term 'chromophore' in UV-Vis spectroscopy refers to:
7. Which functional group would exhibit a characteristic C=O stretching vibration in the IR spectrum at approximately 1650 cm⁻¹?
8. In mass spectrometry, the mass-to-charge ratio (m/z) of the molecular ion peak directly provides:
9. What is the common term for the absorption of light by a molecule causing an electron to move from a lower energy orbital to a higher energy orbital?
10. Which statement about ¹³C NMR is generally true compared to ¹H NMR?
11. The fingerprint region in an IR spectrum (typically below 1500 cm⁻¹) is useful for:
12. Which type of mass spectrometry ionization technique is suitable for analyzing non-volatile and thermally labile compounds?
13. In ¹H NMR, what does a triplet signal usually indicate?
14. A bathochromic shift in UV-Vis spectroscopy is characterized by:
15. What is the primary information obtained from the IR spectrum of an organic compound?
16. The number of signals in a ¹³C NMR spectrum generally corresponds to:
17. Which of the following is NOT a common fragmentation pathway in Electron Ionization (EI) mass spectrometry?
18. In ¹³C NMR, a carbon atom in a carbonyl group (C=O) typically appears in which chemical shift range?
19. What is the principal quantum number (n) in the context of atomic orbitals, relevant to understanding electronic transitions in UV-Vis?
20. The disappearance of a characteristic absorption band in the IR spectrum upon addition of D₂O is a test for the presence of:
21. A singlet signal in a ¹H NMR spectrum indicates that the proton(s) giving rise to that signal have:
22. Which of the following techniques is most useful for determining the molecular weight of a large biomolecule like a protein?
23. In ¹H NMR, what is the approximate chemical shift range for protons attached to an sp² hybridized carbon atom (alkene or aromatic)?
24. The intensity of a signal in UV-Vis spectroscopy is quantified by:
25. Which of the following functional groups typically shows a strong O-H stretching band in the region of 3200-3600 cm⁻¹ in IR spectroscopy?
26. In ¹³C NMR, what is the typical chemical shift range for carbons in aromatic rings?
27. What is the significance of the Nuclear Overhauser Effect (NOE) in NMR spectroscopy?
28. The phenomenon of conjugation in organic molecules leads to a shift in the UV-Vis absorption maximum to longer wavelengths. This shift is called:
29. In IR spectroscopy, bending vibrations are typically observed at:
30. Which ionization technique is commonly used for volatile and thermally stable organic compounds in MS?
31. What information can be deduced from the fragmentation pattern in a mass spectrum?
32. The base peak in a mass spectrum is defined as the peak with:
33. What is the primary purpose of the 'mass analyzer' in a mass spectrometer?
34. In Mass Spectrometry (MS), what is the 'molecular ion' (M⁺)?
35. Which type of solvent is typically used in NMR spectroscopy to avoid interfering signals with the analyte protons?
36. What information can be directly obtained from the integration of signals in a ¹H NMR spectrum?
37. In ¹³C NMR spectroscopy, what is the primary technique used to simplify the spectra by decoupling the carbon nuclei from the attached protons?
38. Which type of carbon atoms in a molecule are generally observed at higher chemical shifts (downfield) in ¹³C NMR spectroscopy?
39. What is the typical range of chemical shifts (in ppm) for protons attached to an sp³ hybridized carbon atom in ¹H NMR?
40. According to the n+1 rule in ¹H NMR, if a proton has 'n' equivalent neighboring protons, its signal will be split into how many peaks?
41. The splitting of signals in ¹H NMR spectra, known as spin-spin coupling, is caused by the magnetic influence of:
42. In ¹H NMR, what is the typical reference compound used to define the zero point of the chemical shift scale?
43. What does the chemical shift (δ) in ¹H NMR spectroscopy represent?
44. In Nuclear Magnetic Resonance (NMR) spectroscopy, what property of atomic nuclei is essential for them to be observable?
45. Which type of electronic transition is most commonly observed in UV-Vis spectroscopy for simple saturated hydrocarbons?
46. The energy difference between the ground state and the excited state of a molecule is related to the wavelength of light absorbed in UV-Vis spectroscopy by which equation?
47. What phenomenon does UV-Vis spectroscopy measure?
48. A strong absorption band around 1700-1750 cm⁻¹ in an IR spectrum typically indicates the presence of which functional group?
49. In IR spectroscopy, what type of molecular vibration involves a change in bond length?
50. Which region of the electromagnetic spectrum is primarily used in Infrared (IR) spectroscopy for organic molecule analysis?