Orgo 2 Weldegirma Exam 1

Name

Problem and Overall Score

1. /10 4. /8 7. /10

2. /20 5. /12 8. /8

3. /10 6. /10 9. /12

Total: /100

1. (10 points) Multiple choice. Circle the correct answer in the following reactions.

i. Which measures the degree of shielding in NMR spectroscopy?

a) coupling constant b) chemical shift c) peak intensity d) signal splitting e) all except a

ii. Which is the correct rank in terms of increasing chemical shifts of the carbon atoms in the compound shown below in 13C NMR?

[pic]

iii. Which reactive intermediates are detected in MS to offer the characteristic peaks?

a) radicals b) radical cations c) carbocations d) neutral molecules

e) a and d f) b and c

iv. The ratio of the heights of the M+ and M++2 peaks is nearly 3:1 in a mass spectrum of an unknown sample. Which of these atoms is most likely present in the unknown?

a) fluorine b) chlorine c) bromine d) iodine e) none of these

v. Which diene is the least reactive in Diels-Alder reactions?

[pic]

2. (20 pts) Match the following structures with the IR spectra shown below.

[pic]

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3. (10 pts) The MS shown below belongs to ethyl butyrate, CH3CH2CH2COOCH2CH3. Explain the formation of the fragments at m/z 88 and 43 by clearly showing the mechanism of the formation of each fragment. Use arrows to show all electron movements for full credits.

[pic]

a) m/z 88

b) m/z 43

4. (8 pts) Consider the MS spectrum shown below.

[pic]

a) ( 3 pts) From the isomers listed below, circle the one that belongs to the spectrum.

[pic]

b) (5 pts) Justify your answer for q.4a by showing a mechanism for characteristic fragmentations in the ketone.

5. (12...