MCQ
1. The approximate value of methyl proton in NMR is
(A) 1.3
(B) 1.5
(C) 0.9
(D) 2.5
2. Boltzmann distribution indicates
(A) The relative no. of protons presents in the excited state and ground state
(B) Relative no. of neutrons presents in the excited state and ground state
(C) Relative no. of nucleus presents in the excited state and ground state
(D) All of the above
3. In NMR spectrum the nuclei in up field resonate at
(A) High frequency
(B) Low frequency
(C) It is constant throughout the spectrum
(D) It doesn’t depend on chemical shift
4. The nuclei that doesn’t give NMR signal is
(A) 15N
(B) 11B
(C) 19F
(D) 31P
5. Signal splitting in NMR arises from
(A) Shielding effect
(B) Spin-spin decoupling
(C) Spin-spin coupling
(D) Deshielding effect
Sample Question:
1. a) Explain the term "Coupling Constant" of the protons in 1HNMR spectroscopy.
b) Comment on the NMR activity of the following nuclei: 14N, 2D.
2. a) Comment on the chemical and magnetic equivalence of vinyl protons of trans-stilbene (1)
b) Give the approximate chemical shift values (d ppm) of the underlined protons of the following compound
3 a) Explain the terms 'chemical equivalence' and 'magnetic equivalence' in connection with proton magnetic spectroscopy with an example for each case.
. b) Why chemical shift of a proton is expressed in d ppm?
c) Arrange the coupling constants of the indicated protons (Ha and Hb) of the following compounds in order of decreasing value.
d) Give approximate d (ppm) values of the underlined protons of the following compounds.
4. a) Distinguish the following pairs of organic compounds by spectroscopic means (as directed).
6. a) Whereas alkene protons appear in the range d 4-8 ppm, alkyne protons appear around d 1.5-3.5. Explain.