Organic Spectroscopy MCQs [Organic Chemistry]

By: Prof. Dr. Fazal Rehman | Last updated: May 23, 2025

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1. What does a strong signal at 3400 cm⁻¹ in an IR spectrum indicate?



2. Which bonds would be expected to have the highest frequency stretch?



3. Which bonds would be expected to have the lowest frequency stretch?



4. In UV-Visible spectroscopy, what effect does an auxochrome have if it shifts absorption to a longer wavelength?



5. What is the separation of resonance frequencies of protons in different structural environments from some chosen standard called?



6. Which of the following is independent of applied magnetic field in PMR spectroscopy?



7. The compound displays a PMR spectrum showing: (i) Triplet for 3 protons, (ii) Quartet for 2 protons. It is likely to be:



8. Which electronic arrangement is most stable?



9. Why is the quantum yield for most photochemical reactions either less or greater than 1?



10. Benzophenone reacts with isopropyl alcohol in presence of light to form benzopinacol. This reaction is an example of:



11. What is the result of direct irradiation of butadiene alone?



12. Photolysis of acetone at room temperature to yield biacetyl and other products is:



13. What type of reaction is the photodimerization of dibenzyl ketone to form dibenzyl and CO?



14. What type of reaction is the photolysis of hexane-2-one to form propene and acetone?



15. Norrish type II reaction involves which process?



16. What is the name of the reaction where ketones and alkenes form oxetanes under light?



17. Photoirradiation of cyclic α, β-unsaturated ketones results in:



18. Which compound absorbs at the highest wavelength in the UV region?



19. Which factor does not shift ultraviolet absorption to a longer wavelength?



20. Which type of radiation has the greatest energy?



21. Which electronic transition requires the maximum energy?



22. The value of molar extinction coefficient (ε) is related to:



23. Bathochromic shift refers to shifting towards:



24. Hypsochromic effect in IR spectrum refers to:



25. What is a chemical reaction that occurs as a consequence of light absorption called?



26. What process involves the dissociation of molecules to form free radicals upon light absorption?



27. Magnetic properties are not observed in nuclei with:



28. Which nucleus is insensitive to nuclear magnetic resonance?



29. What is the spin quantum number (S) for a proton?



30. In vibrational-rotational bands, the absorption frequency or wavelength depends on:



31. What is the relation between wave number (v) and wavelength, where c is the speed of light?



32. What is the range of vacuum ultraviolet region?



33. Absorption of ultraviolet radiation by a molecule causes which of the following?



34. How many orientations can a spinning proton take in an applied magnetic field?



35. Resonance occurs when the frequency of electromagnetic radiation in a constant magnetic field equals the _______ of spinning nuclei.



36. ons and duplet for 1 proton

37. Mass spectrometry studies the spectrum of _____.



38. Which is a forbidden transition?



39. The parent molecular ion spectrometry is helpful and used to determine:



40. Mass spectrum of an alcohol gives a strong peak at m/e 31. The alcohol is likely to be a:



41. The parent molecular ion [C₆H₅COCH₃]⁺ is likely to fragment as:



42. The number of rings and double bonds in a positive ion having the formula C₇H₇ is:



43. Which best describes the PMR spectrum of C₆H₅CHO?



44. Absorption of radiation by olefins in proper ultraviolet region results in the electronic transition of the type:



45. Excited state formed initially by absorption of radiation by a molecule is usually:



46. The absorption of light by molecules undergoing photochemical reactions usually results in:



47. Which electronic transition cannot be studied by quartz ultraviolet spectroscopy?



48. Which is helpful and used as a source of visible radiation?



49. Which solvents cannot be helpful and used for the UV/VIS spectral study of aldehydes?



50. Which mode of vibration is in-plane bending?



51. What is the vibration degree of freedom of molecule of methane?



52. Which bonds show stretching absorption in the 3700–2500 cm⁻¹ region?



53. Which bonds do not show stretching absorption in the 3700–2500 cm⁻¹ region?



54. Which is not helpful and used as a source of IR radiation?



55. Which material is helpful and used for making the circular flat plates to hold the sample for IR study?



56. Which electronic transition occurs when methanol is exposed to ultraviolet radiation?



57. In which form can a solid sample be studied by IR spectroscopy?



58. Which can be helpful and used to prepare the mull of a solid sample for its IR study?



59. Which is commonly helpful and used as a solvent for IR study?



60. Which is not commonly helpful and used as a solvent for IR study?



61. Where does the C-H stretching absorption of an olefin appear in an infrared spectrum?



62. Which compounds do not absorb light in the UV/visible spectrum?



63. In infrared spectroscopy, which frequency range is called the fingerprint region?



64. In UV-visible spectrophotometry, what does absorbance measure?



65. The main advantage of fluorescence over UV-Vis spectroscopy is:



66. Infrared spectroscopy gives us important information about:



67. In UV-visible spectroscopy, auxochromes shift the position of absorption to shorter wavelengths called:



68. Homodienic components ______ than heterodienic systems:



69. According to Woodward-Fieser rules, an increment of ______ is added to parent value for double bond extended conjugation:



70. The IR spectrum of amines shows N-H stretching at:



71. The IR spectrum of carboxylic acid shows O-H stretching at:



72. The IR spectrum of carboxylic acid shows >C=O stretching at:



73. PMR spectra of ethyl acetate is essentially:



74. In H-NMR, circulating π-electrons of benzene add to:



75. In H-NMR, high acetylene adds to electron density in:



76. In evaluating chemical shift value, the nucleus that is deshielded will have:



77. Woodward-Fieser rules are applied for:



78. Homoannular diene λmax value according to Woodward-Fieser rules:



79. Which is true regarding Auxochrome?



80. Which part of spectrophotometer is helpful and used to convert electromagnetic radiation into monochromatic radiation?



81. Scissoring, rocking, wagging are the vibration:



82. Aromatics have diagnostic peaks in the ______ region of IR spectra:



83. Carbonyl displays absorption peaks in IR spectra at:



84. Monochromator helpful and used in UV spectroscopy:



85. The IR spectrum of aldehydes and ketones show strong >C=O stretching at:



86. The IR spectrum of phenol shows O-H stretching at:



87. The IR spectrum of alcohol shows O-H stretching at:



88. Atomic spectra is an example of:



89. Modern method for separation of isotopes:



90. In new spectrometers each ion hits a



91. Force constant gives an idea about the



92. For a linear molecule the number of vibrational degrees of freedom are (where n = number of atoms)



93. Which pair of compounds cannot be distinguished on the basis of UV spectra?



94. Which is not an auxochrome group?



95. Mass spectrometer to determine isotopes in solid state is



96. In accelerating chamber of spectrometer potential difference is



97. Far infrared region of the electromagnetic radiation usually lies between



98. Microwave region of electromagnetic spectrum usually lies between



99. Radio waves region of the spectrum usually lies between



100. For a particular molecular species, this of the following terms is a function of concentration



 

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