CHM3122 MT2 2022 Blank
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Course
3122
Subject
Chemistry
Date
Jan 9, 2024
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5
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1
CHM 3122 Spec
Mid Term 2 Answers
1)
The following is a 90 MHz spectrum of effluvium in CDCl3 with peak pickings given in Hz.
a)
Identify the sub-spectra that should be used to determine the EXACT values for the chemical
shifts and coupling constants in this system (do NOT solve for the exact values, just list the
peaks used for the calculations (
3 Points
)
A
B
C
366.777
357.759
221.958
or
208.485
353.277
344.268
180.810
194.292
344.268
339.102
330.777
325.593
b)
Identify the sub-spectra that should be used to determine the APPROXIMATE values for the
chemical shifts and coupling constants in this system (
3 Points
)
A
B
C
366.777
344.268
208.485
357.759
339.102
203.310
353.277
330.777
199.467
344.268
325.593
194.292
c)
Using your answer for part b, apply the APPROXIMATION method to derive all the chemical
shifts (
) and coupling constants (J) (
3 Points
)
A
B
C
= 355.522
= 334.930
= 201.38
= 3.95
= 3.72
= 2.24
J = 9.0
J = 5.2
J = 5.2
J = 13.5
J = 13.5
J = 9.0
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
4.1
4.2
4.3
ppm
180.810
194.292
199.467
203.310
208.485
221.958
325.593
330.777
339.102
344.268
353.277
357.759
366.777
⑲
t
-
N
a
g
A
⑤
\}°
!?
2
2) Assign all of the signals in the
1
H NMR spectrum of the compound shown below. The solvent was
CDCl
3
. Note: The labels C, H and I are not used. (
8 points
)
3)
a)
How many different resonances are expected for the compound shown below? (
2 Points
)
6
b)
Draw the expected couplings (which protons does the H couple to) and appearance of the
signal for the proton indicated (
4 Points
)
K
G
A
B
E
E
D
F
⑳
G
a
da
qu
d
Al
·
No.
~
...
⊥
a
⑱
3
4) For the compounds shown below
a)
Are the indicated protons chemically equivalent? Briefly justify your answer (
2 Points
)
No. They are not homotopic or enantiotopic (they are diastereotopic)
b)
Are the indicated protons magnetically equivalent? Briefly justify your answer (
4 Points
)
5) For the following first order
1
H NMR spectrum (200 MHz) system perform the following:
a) Draw a splitting diagram for each signal (
6 Points
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
ppm
209.240
216.340
218.340
225.440
227.440
234.540
508.420
512.420
515.420
516.420
519.420
523.420
713.820
719.000
720.920
726.120
A
B
C
-
e
⑤$
->
⑲
=
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4
b)
Derive all coupling constants and chemical shifts (J in Hz and
in ppm) (
9 Points
)
3.60 dd, J = 7.1, 5.2
2.58 dt, J = 7.0, 4.0
1.11 td, J = 9.1, 7.1
c)
Write out the description for signal
C
in proper ACS format for publication (the signal
corresponds to 1 proton). (
2 Points
)
1.11 (td, J = 9.1, 7.1 Hz, 1H)
6)
During an attempted total synthesis, the following by-product was isolated. The molecular formula of
the compound is C
7
H
14
O
3
. The IR spectrum displays strong absorbances at 3442 and 1745 cm
-1
.
The resonance at 1.80 exchanges upon addition of D
2
O. Propose a structure for the unknown
material. (
15 Points
)
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
ppm
3.20
3.25
3.30
3.35
ppm
2.15
2.20
2.25
ppm
6.5
9.5
7.0
4.5
9.5
6.0
7.0
4.5
6.0
6.5
A
B
C
D
E
F
G
-
-
-
D
O
⑱
..
*
⑧
5
-
Unsaturations = (2(7)+2-14) ÷ 2 = 1
(2)
-
Integration
2:1:1:1:3:3:3
(1)
-
IR absorbance at 1745 matches amide carbonyl ester
(1)
-
Resonance at 1.80 exchanges; must be OH; this also fits IR absorbance at 3442
(1)
!
O
#
!
.
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