303 10 Exam 2k.pdf
Transcript of 303 10 Exam 2k.pdf
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Chemistry 303, fall, 2010
SECOND EXAMINATION
7:30 PM, NOVEMBER 15th, 2010
Duration: 2.0 hr
Name____________________________________________________________
This is an "open book" examination; you may use anything that is not alive.
Note: if you do not know the complete or specific answer, give a partial or general answer--
WRITE SOMETHING
If you are using a resonance argument in your answer, draw the relevant resonance structures.
Be aware that in Problem VII, you may "purchase" the unknown structure (Z) for a 10-pt penalty. Go to the
front and request the structure of the proctor and he/she will deduct the appropriate points.
Write only in the space provided for each question.
Score:
p2______/13 p3_______/08 p4_______/08
p5_______/07 p6_______/07 p7_______/12
p8_______/15 p9_______/12 p10______/18 Lab:________/14
Lecture total: _________/100 Penalty?_______ Adjusted total:__________/100
There are 11 pages in this exam. In addition, there is a separate spectra supplement which includes tables of (a)nuclear spin values and for common isotopes, (b) isotope distributions, (c) Chemical shift additivity table (7
pages). Turn in only the exam.
PLEDGE:_________________________________________________________________
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I. (07 pts). Consider the isomers, A, B, and C. H CH3
A B C
A. (4 pts) How would you use IR spectroscopy to differentiate between A and C? Give two clear-cut differences.
B. (03 pts). How would you use broad band decoupled 13C NMR spectroscopy to differentiate between B and C? Give the
single most clear-cut difference.
___________________________________________________________________________________________________________
II. (06 pts). Consider the methane derivative, V.
A. (03 pts). What do you predict for the pattern that will be observed in the 1 H NMR spectrum?
Explain carefully.
B. (03 pts). What do you predict for the pattern that will be observed in the 13C NMR spectrum (H broad band decoupled)?
CCl2P
F
Cl
H
V
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III. (08 pts). Consider compound P and its 1H NMR spectrum.
A. (05 pts) Draw the hydrogens on compound P, and assign each type of hydrogen (H a, H b, etc.) to the corresponding NMR peaks,
and the pattern (s, d, t , quartet, quintet, sextet, etc).
PPM
e
d
c
b
a
(1H) (1H)
(4H)
(6H) (6H)
OO
P
B. (03 pts). How many peaks do you predict for the13
C NMR (broad band decoupled)? 4 5 6 7 8 9 10 11 12
(circle single best answer)
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IV. (08 pts). Isomers K and L show distinctly different IR spectra in CCl4 solution.
K: sharp peak at 3300 cm-1
, strong sharp peak at 1700 cm-1
.
L: broad peak at 3300-3500 cm-1; strong sharp peak at 1715 cm-1.
A. (04 pts). Explain the difference in pattern (sharp vs broad) for the peaksaround 3300 cm-1. Include in your answer why the sharp peak for K is at the lowerend of the 3300-3500 cm-1 range.
B. (04 pts). Explain the difference in position (frequency) for the peaks at around 1700-1715 cm-1.
O
OMe
O
OH
K L
OH OMe
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V. (20 pts). A reaction that you will see next semester involves the conversion of acetanilide (1) into TWO of
the three isomeric structures (2, 3, 4).
Upon running the reaction you are pleased to find that the two products (call them X and Y) produced are easily separated
and you are left to identify the structures by spectroscopy. X and Y correspond to two of the three possible structures, 2-4.
A. (02 pts). Would IR spectroscopy be useful in assigning the structures of X and Y, assuming you use the region from
1500-4000 cm-1 only? Explain briefly. For your reference, the spectrum of X is given here:
B. (05 pts). The13
C NMR data (H broad band decoupled) were also collected and are given here:
Isomer X 13C NMR: (! 169.2, 136.5, 135.8, 134.8, 125.6, 123.4, 122.3, 25.5)
Isomer Y 13C NMR: (! 169.2, 145.9, 142.0, 124.4, 118.4, 25.4)
Can you distinguish the isomeric products using 13C NMR alone? Describe specifically the single most clear-cut distinction you can
determine about the isomers X and Y from the 13C NMR spectra and clearly define any ambiguities.
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C. (07 pts). The 1H NMR spectrum of Y is shown here. Draw the structure of Y in the box and explain carefully how it is
consistent with the patterns of peaks between 7 and 9 ppm in this spectrum. You need not deal with relative chemical shifts. Assume
all coupling to H on adjacent carbons is 9 Hz. Ignore long-range coupling.
Y
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D. (12 pts). The 1H NMR spectrum of X is shown here.
1. (08 pts). Draw the structure of X in the box and explain carefully how the patterns between 7 and 9 ppm are consistent with this
spectrum. All of the multiplets in the region show area 1H. You need not analyze relative chemical shifts. Assume all primary
coupling constants are 9 Hz.
2. (04 pts). Explain briefly how the other candidate structure (not Y ) is not compatible with these patterns.
X
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VI. (15 pts). Use the techniques of spectroscopy (UV, IR, MS, 1H NMR, 13C NMR) to distinguish the pairs of molecules
shown. You may use each technique only once. Clearly describe the features that would distinguish the pairs of molecules using the
method selected. With mass spec, you may not use the high resolution technique to give exact molecular formula.
H3C
O O
H3C
O
N
O
CH3
CH3
A.
a b
Method:
Explain:
CH3
CH3
_____________________________________________________________________________
CH3O
OCH3
H3C
H3C CH3
SH3C
c d
Method:
Explain:
B
_____________________________________________________________________________O O
e f
Method:
Explain:
C.
_____________________________________________________________________________
O O
O
CH3H3C
O O
O
H3C CH3
g
h
Method:
Explain:
D.
_____________________________________________________________________________ CH3Cl
Cl ClCl
i j
Method:
Explain:
E.
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VII. (30 pts). Consider the spectral data for compound Z on the separate data sheets.
A. (04 pts). Consider the IR spectrum, from 4000-1500 cm-1. Circle the functional groups that you can rule out from the spectrum
and explain in a phrase with the single clearest element of data (or absent data).
C CH2
R
R
C O
R
R
R Cl
R OH
C N
R
R
R
C CHR
B. (01 pts). Consider the 1H NMR spectrum. How many different types of protons are suggested by the spectrum?
1___ 2___ 3___ 4___ 5___ 6___ 7___ cannot tell____
(check the best answer; explain any ambiguity)
C. (01 pts). Consider the 13C NMR spectrum. How many different carbons are suggested by the spectrum?
1___ 2___ 3___ 4___ 5___ 6___ 7___ cannot tell____(check the best answer; explain any ambiguity)
D. (05 pts). Consider the mass spectrum.
1. What is the molecular weight of the molecule? __________
2. What is your estimate of the number of carbon atoms in the molecule? ___________
3. Which of the following atoms can be ruled out by the mass spectrum alone? (circle all correct answers)
O? N? F? Cl? S? Br?
E. (01 pts). Consider the UV spectral data.
Are there conjugated pi bonds in the structure?
Circle single best answer: YES NO CANNOT TELL
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F. (10 pts). Draw LARGE in the box your best proposal
for the structure of Z. On your structure, label each H (or set
of equivalent H) with a letter for reference (A, B, C, D, etc).
Referring to your structure and labels, please fill in the follow table.
In the column “coupling connections”, list the other H(s) to which the proton
in question is coupled (not coupling constants).
NOTE : you may "buy" the structure Z at a penalty of 10 pts.
_______________________________________________________________
Chemical shift Pattern
(ppm) (s, d, t, etc) Area Coupling connections
A 1.25 6
B 1.92 2
C 2.08 3
D 5.45 1
E 5.95 1
G. (03 pts). Note the peaks centered at ! 1.92 ppm in the 1H NMR spectrum of Z and the proton(s) to which you assign
them in your structure. Explain carefully how this chemical shift position and pattern is consistent with your structure. [If you are not
confident of a structure, just discuss this feature in general terms]. Use the additivity table to support your assignment; show your
work.
H. (03 pts). Note the peaks centered at ! 5.45 ppm in the 1H NMR spectrum of Z and the proton(s) to which you assign them
in your structure. Explain carefully how this pattern is consistent with your structure. [If you are not confident of a structure, just
discuss this feature in general terms].
I. (02 pts). Consider the peak at ! 176 ppm and the peak at ! 31 ppm in the 13C NMR spectrum of X. Draw your structure
here again, and then circle the carbon which appears at 176 and put a square around the carbon which appears at 31 ppm. [If you
are not confident of a structure, just discuss this feature in general terms]
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VIII. (14 pts). Lab-Related Question.
A. (06 pts). In yet another dyslexic moment in the orgo lab, Joe L. Sapphire set up his Oxidation-Reduction reaction employing 10%aqueous NaOH solution (from the Analgesic Experiment), rather than the recommended 50% aqueous NaOH solution. During the
workup of his reaction, he failed to obtain any carboxylic acid upon acidification of the aqueous layer. (Yes, his aqueous solution wasdefinitely acidic!) In an attempt to isolate some of his carboxylic acid, he concentrated his acidic aqueous layer by boiling off somewater. When enough water had been removed, a colorless solid separated. This colorless solid failed to redissolve upon addingethanol to the hot mixture, but did dissolve upon adding additional water. If isolated, the colorless solid failed to melt below 400 °C.(Melting points above 400 °C cannot be safely taken on our melting point apparatus.) What was this colorless solid, and how did it form?
B. (08 pts). Steam distillation of ocimum basilicum L. affords basil oil, which is composed of about 80% estragole (X). Spectral datafor estragole (X) are summarized below.
mass spectrum: m/ z = 148 (M, 100%), 149 (11%)
IR (liquid film): 3077-2835 (multitude of weak peaks), 1640 (m), 1611 (m), 1511 (s), 1301 (m), 1247 (s), 1176 (s), 1038 (s), 992(m), 914 (m), and 810 (m) cm
-1
[There are no absorptions in the 3100-4000 cm-1 region of the spectrum. m = medium, s = strong]
Choose (circle) the best structure for estragole ( X ) from the four possible structures ( 1-4 ) shown below. Please briefly explain how
you eliminated each of the incorrect structures for X . (Hint: You do not need to utilize any absorptions in the “fingerprint” region ofthe IR spectrum of X to answer this question.)
CH3
H
CH3
H
C
NO2
N OCH3
OH
H3C
1 2 3 4
End exam