Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Questions previous years

1,589 views

Published on

Previous years questions from Spectroscopy

Published in: Education
  • Be the first to comment

Questions previous years

  1. 1. Previously asked Questions from Spectroscopy Presented by Dr. Abiram
  2. 2. 1. The absorbance of solution having 20% transmittance is a. 0.301 b. 0.699 c. 1.301 d. 1.699
  3. 3. 2. In a broad band decoupled 13C NMR Spectrum, the number of signals appear for  1. Catechol  2. Resorcinol  3. Hydroquinone are: a) Six, four and two b) Six, six and four c) Three, four and four d) Three, four and two
  4. 4. 3. The order of carbonyl stretching frequency in the IR spectra of ketone, amide and anhydride a. Anhydride > Amide> Ketone b. Ketone > Amide > Anhydride c. Amide > Anhydride > Ketone d. Anhydride > Ketone > Amide
  5. 5. 4. The absorption at λmax 279 nm for Acetone is due to a) n __> π* b) π __> π* c) n __> σ* d) σ __> σ*
  6. 6. 5. A liquid compound gave a mass spectrum showing a strong molecular ion at m/z = 156. The only fragment ions are seen at m/z = 127 & 29.  What are the fragments and what is the structure?
  7. 7. 6.  A liquid compound gave a mass spectrum in which the molecular ion appears as a pair of equal intensity peaks at m/e = 122 & m/z = 124. Small fragment ion peaks are seen at m/z = 107 & 109 (equal intensity), and at m/z = 79, 80, 81, & 82 (all roughly the same size). Large fragment ions are seen at m/z = 43 (base peak), 41 & 39. Suggest the name of the compound
  8. 8. a. 2-chloro propane b. 1-bromo propane c. 2-chloro butane d. 1-bromo butane
  9. 9. 7. The number of normal modes of vibration for C6H6 would be a. 20 b. 30 c. 40 d. 50
  10. 10. 8. Which classes of compounds are found in the highly deshielded region of an NMR spectrum? a. Sp3 hybridised alkanes b. Alkenes and SP hybridised alkynes c. TMS d. Carboxylic acids and Aldehydes
  11. 11. 9. A carbon atom has three hydrogens attached to it, and its nearest neighbor has one hydrogen. The NMR spectrum will contain at least -  a) a triplet with an area of 3 and a singlet with an area of 1  (b) a singlet with an area of 3 and a singlet with an area of 1  (c) a quartet with an area of 1 and a doublet with an area of 3  (d) a quartet with an area of 3 and a doublet with an area of 1
  12. 12. 10. How many absorptions will the following compound have in its carbon NMR spectrum? a. 3 b. 4 c. 5 d. 6
  13. 13. 11. The CMR spectrum of an unknown compound shows 6 absorptions and the PMR spectrum shows 5 absorptions. Which of the following compounds is the unknown compound?
  14. 14. 12. The CMR spectrum of an unknown compound shows 4 absorptions and the PMR spectrum shows 4 absorptions. Which of the following compounds is the unknown compound?
  15. 15. Answer Explanantion  There should be equal numbers of absorptions in both spectra and there are 4 unique positions in the molecule. Note that the molecule is symmetrical with respect to the red line...
  16. 16. 13.In 2,2,4-trimethyl pentane the base peak is observed at m/z a. 43 b. 41 c. 28 d. 57
  17. 17. 14.The base peak formed for the friedal-crafts alkylation of bromobenzene is observed at m/z a. 156 & 158 b. 171 & 173 c. 77 & 79 d. 91 & 93
  18. 18. 15. Which of the following bonds would show the strongest absorption in the IR? a. carbon-oxygen b. Oxygen-hydrogen c. Nitrogen-Hydrogen d. Sulfur- hydrogen
  19. 19. 16. The compound that exhibit sharp bands at 3300cm-1and 2150cm-1 in IR Spectra is a. 1-Butyne b. 2-Butyne c. Butyronitrile d. Butylamine
  20. 20.  Nitrile C=N Stretch 2260 – 2120  =C-H Stretch : 3100-3300 cm-1
  21. 21. 17. The H NMR spectrum of a dilute solution of a mixture of Acetone and dichloromethane in CDCl3 exhibits two singlets of 1: 1intensity. Molar ratio of Acetone to dichloromethane is a. 3:1 b. 1:3 c. 1:1 d. 1:2
  22. 22. 18. Intense band generally observed for a carbonyl group in a IR spectrum is due to a. The force constant of CO bond is large b. The force constant for CO bond is small c. There is no change in dipole moment for CO bond stretching d. The dipole moment change due to CO bond stretch is large
  23. 23. Explanation  Bond Vibration The energy of the infrared light can interact with the resonant vibrational frequency of the bond Since different bonds have different energies, they require different energy to cause vibration.
  24. 24.  Intensity of Absorbance  Intensity of light absorbed by a molecule is related to the dipole of the bond  The greater the dipole, the greater the absorbance intensity C-O bond stretches are therefore more intense than C-C stretches
  25. 25. 19. The mass of metastable ion produced due to decomposition of F1in the following mass fragmentation sequence is Diethylphthalate F1 + F2 + CO 222 177 a. 141.2 b. 125.4 c. 45 d. 210.2
  26. 26. M1 = Molecular ion mass m1 = daughter ion peak
  27. 27. Answers: 1. B 2. D 3. D 4. C 5. A 6. B 7. B 8. D
  28. 28. 9. C 17. A 10. D 18. D 11. B 12. A 13. D 14. A 15. B 16. A

×