Instrumental Analysis - Spectroscopy Questions PDF

1. Which analytical technique can be used to identify functional groups in organic molecules? * A) Mass spectrometry * B) Infrared spectroscopy * C) NMR spectroscopy * D) Gas chromatography 2. What does infrared (IR) spectroscopy measure? * A) The mass of molecule...

1. Which analytical technique can be used to identify functional groups in organic molecules? * A) Mass spectrometry * B) Infrared spectroscopy * C) NMR spectroscopy * D) Gas chromatography 2. What does infrared (IR) spectroscopy measure? * A) The mass of molecules * B) The absorption of infrared radiation by chemical bonds * C) The arrangement of carbon and hydrogen atoms in a molecule * D) The rotation of plane-polarized light 3. Different types of bonds absorb IR radiation at... * A) The same wavenumber * B) different wavenumbers * C) all bonds absorb equally * D) depends on the molecule 4. What is "wavenumber" proportional to? * A) Wavelength * B) Frequency * C) Mass * D) Charge 5. What is the approximate wavenumber range for the " ngerprint region" in an IR spectrum? * A) 4000-1500 cm-1 * B) 1500-500 cm-1 * C) 500-100 cm-1 * D) 100-0 cm-1 6. The ngerprint region of an IR spectrum is... * A) Unique to a speci c compound * B) The same for all organic compounds * C) Used to identify the overall class of compound (e.g., alcohol) * D) Not useful for identi cation 7. Which of the following bonds would you expect to see a strong, broad absorption for in an IR spectrum? fi fi fi fi * A) C-H * B) C=C * C) O-H (in alcohols) * D) C-C 8. A sharp peak at approximately 1700cm-1 indicates which of the following bonds? * A) C-H * B) C=C * C) O-H (in alcohols) * D) C=O 9. What information does mass spectrometry provide? * A) Functional groups present * B) Molecular mass and fragmentation pattern * C) Arrangement of atoms in space * D) Types of chemical bonds 10. What is the "molecular ion peak" (M+) in a mass spectrum? * A) The peak with the lowest m/z value * B) The peak with the highest m/z value, corresponding to the unfragmented molecule * C) The most intense peak * D) The peak corresponding to a fragment with a +2 charge 11. The M+ peak represents a species with what charge? * A) -1 * B) 0 * C) +1 * D) +2 12. The molecular ion is formed by... * A) Loss of one proton * B) Gain of one electron * C) Loss of one electron * D) gain of one proton 13. What causes fragmentation in a mass spectrometer? * A) The molecule absorbing infrared radiation * B) The molecule colliding with other molecules * C) The breaking of covalent bonds in the molecular ion * D) The molecule rotating 14. Fragment ions in a mass spectrum are... * A) Neutral * B) Negatively charged * C) Positively charged * D) a mixture of positive and negative 15. What is the m/z value? * A) mass x charge * B) mass + charge * C) mass - charge * D) mass / charge 16. How can mass spectrometry be used to distinguish between two compounds with the same molecular mass? * A) They will have different molecular ion peaks. * B) They will have different fragmentation patterns. * C) They will absorb infrared radiation differently. * D) Mass spectrometry cannot distinguish between them. 1. What does NMR stand for? * A) Neutral Mass Resonance * B) Nuclear Magnetic Resonance * C) Nucleus Mass Radiation * D) Nuclear Molecular Radiation 2. Which nuclei are commonly studied using NMR spectroscopy? * A) 1H and 12C * B) 1H and 13C * C) 2H and 12C * D) 2H and 13C 3. What property of nuclei allows them to be studied by NMR? * A) Mass * B) Charge * C) Spin * D) Size 4. What happens to nuclei with spin in a strong magnetic eld? * A) all nuclei align at 90 degrees to the eld * B) They align randomly * C) They align with or against the eld * D) They precess perpendicular to the eld 5. What is "chemical shift" in NMR? * A) movement of atoms in a molecule * B) The difference in the absorption frequency of a nucleus compared to a standard * C) The splitting of NMR signals * D) The intensity of an NMR signal 6. What is the standard reference compound commonly used in NMR spectroscopy? * A) CHCl3 (trichloromethane) * B) TMS (tetramethylsilane) * C) H2O (water) * D) CCl4 (tetrachloromethane) 7. Why is TMS a suitable standard reference compound? * A) a single, large absorption, down eld of most absorptions. * B) a single, large absorption, up eld of most absorptions * C) multiple, large absorptions, down eld of most absorptions. * D) multiple, small absorptions, down eld of most absorptions. 8. What does the number of peaks in a 13C NMR spectrum (ignoring splitting) generally indicate? * A) The number of hydrogen atoms in the molecule * B) The number of different carbon environments in the molecule * C) The number of functional groups in the molecule * D) The molecular mass of the molecule 9. What does the n+1 rule describe in 1H NMR? * A) the chemical shift of a peak * B) The splitting pattern of a peak due to neighboring, non-equivalent H atoms * C) The number of peaks in a 13C NMR spectrum * D) The relative intensity of peaks fi fi fi fi fi fi fi fi  10. What does the integration trace (or area under the peak) in a 1H NMR spectrum indicate? * A) The chemical shift of the peak * B) The number of neighboring H atoms * C) The relative number of H atoms in that environment * D) The splitting pattern Answers and Explanations: 1. B) Nuclear Magnetic Resonance - This is the correct name. 2. B) 1H and 13C - These isotopes have the necessary nuclear spin. 3. C) Spin - Nuclear spin is the key property. 4. C) They align with or against the eld - This creates two energy levels. 5. B) The difference in the absorption frequency of a nucleus compared to a standard - This difference is due to the chemical environment. 6. B) TMS (tetramethylsilane) - TMS is the standard reference. 7. B) a single, large absorption, up eld of most absorptions Correct de nition. 8. B) The number of different carbon environments in the molecule - Each unique carbon environment gives a separate peak. 9. B) The splitting pattern of a peak due to neighboring, non-equivalent H atoms - n+1 rule predicts the multiplicity. 10. C) The relative number of H atoms in that environment - The area is proportional to the number of H atoms causing the peak. Powered by pmfm.ai Request Support fi fi fi  Answers and Explanations: 1. B) Infrared spectroscopy - IR spectroscopy identi es functional groups based on bond vibrations. 2. B) The absorption of infrared radiation by chemical bonds - This is the fundamental principle of IR spectroscopy. 3. B) different wavenumbers - correct de ntion 4. B) Frequency - Wavenumber is directly proportional to frequency. 5. B) 1500-500 cm-1 - This region is complex and unique to each compound. 6. A) Unique to a speci c compound - Like a human ngerprint, it's highly speci c. 7. C) O-H (in alcohols) - O-H bonds show a characteristic broad absorption. 8. D) C=O - This is a very characteristic peak for carbonyl compounds. 9. B) Molecular mass and fragmentation pattern - These are the key pieces of information from mass spec. 10. B) The peak with the highest m/z value, corresponding to the unfragmented molecule - This represents the whole molecule with a single positive charge. 11. C) +1 The molecular ion has lost on electron. 12. C) Loss of one electron 13. C) The breaking of covalent bonds in the molecular ion - The high- energy electron beam causes bonds to break. 14. C) Positively charged Fragment ions are formed by bond breaking fi fi fi fi fi and electron loss. 15. D) mass / charge de nition. 16. B) They will have different fragmentation patterns. - Even with the same molecular mass, different structures will fragment differently. 17. B) Boiling point and interaction with the stationary phase - These factors determine how quickly a compound moves through the column. 18. B) The time it takes for a speci c compound to pass through the column - This is the de nition of retention time. 19. B) The relative amount (concentration) of each component - The area is proportional to the amount of substance. 20. B) Mass spectrometry - GC-MS is a powerful combination for separating and identifying compounds. Powered by pmfm.ai Request Support fi fi fi