The University of Tulsa Department of Chemistry ...

1

Full Name____________________________________________

Chemistry 3013-01

The University of Tulsa

Department of Chemistry & Biochemistry

Organic Chemistry I

Examination 3

March 16, 2012

DO NOT OPEN THIS EXAM UNTIL DIRECTED TO DO SO When the exam begins, please look through every question to quickly assess how to best allocate your time. You must answer all questions. An optional bonus problem is also available; it is worth up to 10 points. The point value for each question is designated in parentheses after each problem. The exam will last from 1:00 PM until 1:50 PM. When time is called, you must put down your pencil immediately and hand in the exam. Please write and draw as clearly as possible in the space provided. If you require additional space and continue an answer on the back of a page, you must clearly indicate this to the grader.

Question 1: Interpreting IR spectra (20 pts) ____

Question 2: Designing NMR experiments (20 pts) ____

Question 3: UV-VIS spectroscopy and Mass Spectrometry (20 pts) ____

Question 4: Structural assignment of an unknown compound (20 pts) ____

Question 5: Full 1H and 13C NMR assignment (20 pts) ____

Bonus: Interpreting 1H chemical shifts ____

Total ____

2

Question 1: Match the compounds shown below to their corresponding IR spectrum. Briefly justify your proposal by labeling the diagnostic peaks in the appropriate spectrum. (10 pts)

N

O

H and H3C C N

3

(Question 1 continued) Match the compounds shown below to their corresponding IR spectrum. Briefly justify your proposal by labeling the diagnostic peaks in the appropriate spectrum. (10 pts)

CH3N3

NO2

and

CH3

4

Question 2: Propose an NMR experiment or series of experiments that can be used to distinguish the following compounds. Explain your proposal. (10 pts)

O

O

O

Oand

5

(Question 2 continued) Propose an NMR experiment or series of experiments that can be used to distinguish the following compounds. Explain your proposal. (10 pts)

O

OMeH3CO

OMe

H3C

O

OMe

CH3

and and

6

(Question 2 continued)

7

Question 3: Match the compounds below to their corresponding UV-VIS spectrum. Briefly justify your assignment. (10 pts)

Styrene

and

trans-stilbene

Spectrum A: λmax = 245 nm Spectrum B: λmax = 296 nm

3/11/12 6:12 PM

Page 1 of 2http://webbook.nist.gov/cgi/cbook.cgi?Spec=C100425&Index=0&Type=UVVis&Large=on&SVG=on

NIST Chemistry WebBook (http://webbook.nist.gov/chemistry)

StyreneUV/VIS SPECTRUM

Wavelength (nm)

Loga

rithm

eps

ilon

230 240 250 260

3.2

3.6

4

3/11/12 6:12 PM

Page 1 of 2http://webbook.nist.gov/cgi/cbook.cgi?Spec=C588590&Index=0&Type=UVVis&Large=on&SVG=on

NIST Chemistry WebBook (http://webbook.nist.gov/chemistry)

1,2-DiphenylethyleneUV/VIS SPECTRUM

Wavelength (nm)

Loga

rithm

eps

ilon

240 280 320

2

2.5

3

3.5

4

8

(Question 3 continued) The EI-MS for benzyl chloride is shown below. First, identify and label the molecular ion peak(s) in the EI-MS. Second, explain the peak observed at m/z = 91. (10 pts)

ClAtomic masses:(Relative abundance is given for chlorine)

C = 12.00H = 1.01Cl = 34.97 (100%), 36.97 (32%)C7H7Cl

9

Question 4: You generate an unknown compound during a reaction. The molecular formula was determined to be C5H10O2 using high-resolution mass spectrometry. Propose a chemical structure that is consistent with the following IR and NMR data. Justify your proposal by labeling diagnostic IR peaks and assign 1H and 13C NMR spectra as fully as possible. (20 pts) IR (neat):

1H NMR (90 MHz, CDCl3): δ = 1.23 (6H, d, J = 6.3 Hz), 2.02 (3H, s), 4.99 (1H, septet, J = 6.3 Hz)

10

(Question 4 continued) 13C NMR (25 MHz): δ = 21.3, 21.8, 67.5, 170.4

21.3 ppm

21.8 ppm

11

(Question 4 continued)

12

Question 5: Fully assign the 1H and 13C NMR spectra for the following compound. Label your assignments directly on the spectra provided. COSY and HSQC spectra are provided to assist in your assignment. (20 pts)

O

O O

O

Tabulated data: 1H NMR (400 MHz, CDCl3): 1.26 (6H, t, J = 7.1 Hz), 2.00 (1H, t, J = 2.5 Hz), 2.75 (2H, dd, J = 7.7, 2.5 Hz), 3.54 (1H, t, J = 7.7 Hz), 4.21 (4H, q, J = 7.1 Hz) (Solvent peak is at δ = 7.27) 13C NMR (100 MHz, CDCl3): 14.0, 18.3, 51.1, 61.7, 70.3, 79.9, 167.8 (Solvent peak is a triplet at δ = 77.0)

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Chemical Shift (ppm)

6.000.852.010.883.91

1.24

1.26

1.27

1.99

2.00

2.01

2.74

2.75

2.76

2.76

3.52

3.54

3.56

4.18

4.20

4.22

4.23

7.27

This report was created by ACD/NMR Processor Academic Edition. For more information go to www.acdlabs.com/nmrproc/

200 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 0Chemical Shift (ppm)

13.9

5

18.3

1

51.0

6

61.7

0

70.3

1

76.6

877

.00

77.3

379

.89

167.

78

This report was created by ACD/NMR Processor Academic Edition. For more information go to www.acdlabs.com/nmrproc/

propargyl diethyl malonate full nmr Feb04-2010-57.004.001.2rr.esp

4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5F2 Chemical Shift (ppm)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

F1 C

hem

ical

Shi

ft (p

pm)

This report was created by ACD/NMR Processor Academic Edition. For more information go towww.acdlabs.com/nmrproc/

HSQC.ESP

4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5

F2�Chemical�Shift�(ppm)

0

8

16

24

32

40

48

56

64

72

80

88

96

104

112

120

128

136

144

152

F1

�Ch

em

ica

l�S

hift�

(pp

m)

This�report�was�created�by�ACD/NMR�Processor�Academic�Edition.�For�more�information�go�towww.acdlabs.com/nmrproc/

16

Bonus: The following compound—from a class of materials called annulenes—has two peaks in the 1H NMR spectrum: one peak is at 9.17 ppm and the other peak is at −2.96 ppm. Which protons resonate at these frequencies? Explain your assignment and discuss the reason for the large shielding and deshielding observed in this molecule. (You are not required to discuss multiplicity).

17

(Bonus continued)