Spectroscopy Practice Exam Key

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CHEM – 254 – WI -2009

Problem Set #1 – IR Spectroscopy - KEY
1. Which of the indicated bonds absorbs at the higher frequency in an IR spectrum? a. O or OH

C=O > C-O b.
N or NH

C=N > C-N c.
H or H

C-H sp2 > C-H sp3

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CHEM – 254 – WI -2009

2. What major IR absorptions are present above 1500 cm-1 for each compound?

a.

b.

O sp3 C-H stretch 2950 C=O - ketone 1715 cm-1 cm-1

c. O

sp3 C-H stretch 2950 cm-1

sp3 C-H stretch 2950 cm-1 sp2 C-H stretch 3100 cm-1 C=O - ketone 1715 cm-1 C=C alkene 1680 cm-1 O

O d. e. f.

OH

sp3 C-H stretch 2950 sp C-H stretch 3310 cm-1 CC alkyne stretch 2220 cm-1

cm-1

sp2 C-H stretch 3100 cm-1 sp3 C-H stretch 2950 cm-1 C=C alkene 1680 cm-1

sp2 C-H stretch 3100 cm-1 OH -Stretch 3400-2700 cm-1 C=O carboxylic acid 1725 cm-1 C=C alkene 1680 cm-1

g. OH

h.

OH

i.

Br

sp3 C-H stretch 2950 cm-1 OH -Stretch 3400-3200 cm-1

sp2 C-H stretch 3100 cm-1 OH -Stretch 3400-3200 cm-1 sp3 C-H stretch 2950 cm-1 C=C alkene 1680 cm-1

sp3 C-H stretch 2950 cm-1

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CHEM – 254 – WI -2009

3. How would you distinguish between the following pairs of compounds using IR spectra? a. and

sp2 C-H stretch 3100 cm-1

sp C-H stretch 3310 cm-

b.
O OH and O O

OH -Stretch 3400-2700 cm-1 C=O carboxylic acid 1725 cm-1

C=O esters 1740 cm-1

c.
O and OH OH -Stretch 3400-3200 cm-1 sp2 C-H stretch 3100 cm-1

C=O - ketone 1715 cm-1

d.
O O and O O C=O esters 1740 cm-1

sp3 C-H stretch 2950 cm-1

e.
H and N

sp C-H strech 3310 cm-1

CN stretch 2280 cm-1

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CHEM – 254 – WI -2009

4. Tell how IR spectroscopy could be used to determine when each reaction is complete. a. H2, Pd/C MeOH

Monitor for the disappearance of the C-H sp2 stretch 3100 cm-1

b.
OH PCC, CH2Cl2 O

Monitor for the disappearance of the OH stretch 3200 cm-1 and the appearance of the C=O stretch 1715 cm-1.

c.
1. O3 2. (CH3)2S O O +

Monitor for the appearance of the C=O stretch 1715 cm-1 and the disappearance of the C=C at 1620 cm-1

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CHEM – 254 – WI -2009

5. Match each compound to its IR spectrum.
O OH A-5 B-1 C -4

O O D-3 O E -6

OH

F -2

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CHEM – 254 – WI -2009

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CHEM – 254 – WI -2009

6. Match each compound to its IR spectrum.
O N HO O A B C D E OH H N

C-1, E-2, B-3, D-4, A-5 Spectrum 1

Spectrum 2

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CHEM – 254 – WI -2009

Spectrum 3

Spectrum 4

Spectrum 5

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