SIKKIM UNIVERSITY Department of Chemical Sciences

Instrumental Techniques: CHE-PG-O302End semester: September 2015

Dr. B. G. Roy (Part-1)

Total Marks: 25 Time: 1 h

Section AAnswer all questions (10 x 1 = 10)

1. What is not true about DEPT experimenta. Quaternary carbon does not appear in DEPT experimentb. DEPT 135 show CH and CH3 carbons UP and CH2 carbons downc. DEPT 90 show CH carbons down.d. It is a proton decoupled technique.

2. Match the 19F NMR shifts δ a. -219, b. -116, c. -68, d. -63 with the following compounds.

e. , f., g. , h. and choose the correct match.a. a-e, b-f, c-g, d-hb. a-f, b-g, c-e, d-hc. a-h, b-f, c-g, d-ed. a-g, b-h, c-f, d-e

3. NMR is one of the most insensitive but most useful technique for structure determination of a compound. Which of the following is NOT true about NMR?

a. Sensitivity increases with higher applied magnetic field.b. Sensitivity decreases with higher gyromagnetic ratio of any nuclei.c. Sensitivity is less due to the less difference in population between two states.d. Sensitivity increases with higher natural abundance of NMR active isotope.

4. What is NOT true about HMQC (Heteronucleur multiple quantum coherence)?a. It shows correlation between carbon and hydrogen.b. It is a polarization transfer technique. c. It is much more sensitive compared to C-H COSY.d. It shows 2 and 3 bond correlation between carbon and hydrogen.

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5. INADEQUATE spectrum need very high concentration of sample and long NMR time mainly because

a. 13C has low natural abundance.b. 13C has low gyromagnetic constant.c. Probability of two consecutive carbon nucleus to be 13C is once in 1000 molecule.d. All of the above.

6. Satellite peaks arises due to e. Inhomogeneity of applied magnetic field.f. Improper mechanical rotation of sample tube.g. Heteronuclear coupling with attached 13C.h. Little impurity present in the molecule.

7. Which one could be the correct sequence 19F chemical shifts δF of following compounds?

A) X = H; B) Me; C) t-Bu; D) X = Et

a. A>B>C>Db. C>D>B>Ac. D>C>B>Ad. D>B>C>A

8. What is NOT true about HMBC?a. It 2D NMR technique.b. It is useful to deduce the structural framework of a molecule.c. It shows 2 and 3 bond correlation between carbon and hydrogen.d. It is a proton decoupled technique.

9. Which of the following option is representing the correct values of designated protons?

10. Which of the following protons are chemically equivalent but magnetically non-equivalent?

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a) I, II and IVb) I and IVc) II and IVd) II, III and IVe) None of the above

Section BAnswer any One (1 x 15 = 15)

11. a) Treatment of this keto-aldehyde with KOH gives a compound C7H10O with the spectroscopic

data shown. What is its structure and how is it formed? You should, of course, assign the NMR

spectrum and give a mechanism for the reaction. 4

b) 31P NMR is more sensitive than 19F NMR’- Do you agree or disagree? Give reason

supporting your choice. 1

c) A compound having molecular formula C9H16O4, gives following 1D and 2D NMR spectra.

Draw the structure and assign each atom with NMR value. Give explanation for you logical structural

elucidation and assignments. 8

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d) Comment on the chemical composition of the compound from following mass spectrum. 2

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12. a) Discuss about the difference between EI and ESI mass spectroscopic techniques. 2

b) Predict the compound structure from following EI mass spectra. 2

c) A compound having molecular formula C10H16O, gives following 1D and 2D NMR spectra. Draw

the structure and assign each atom with NMR value. Give explanation for you logical structural

elucidation and assignments. 8

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d) Deduce the structure of following compound having molecular formula C8H19N)? 3

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