CHEM 216H
Exam 1, 2005
Page 1
I. (34 points) In the supplemental material, you fill find the following article: Souers, A.J.; Ellman, J. A.
J. Org. Chem. 2000, 65, 1222-1224 along with other information about the reagents used in the
synthetic transformation you are interested in carrying out:
H
a
TBDPSO
2
3
O
CH3
TBDPS =
TBDPSO
CH3
CH3
O
Ph
Si
...
Ph
a) What is the molecular weight of 2 to two decimal places?
C20H26SiO2 326.55 g/mol Using the values from the periodic table on the cover sheet (C:
12.01, H 1.01, O 16.00, Si 28.09.
2
b) You cannot find a commercial source for the aldehyde 2. Give a full a literature reference
where you would find its synthesis:
Ikeda, Y.; Uka, J.; Ikeda, N.; Yamamoto, H. Tetrahedron 1987, 43, 731-741.
2
c) When you make 2, you only get 2.25 g of product. You use 0.25 g for characterization. You
decide to go ahead with the synthesis of 3 using all of the rest of the aldehyde 2 that you have
made. How much of the following reagents would you use? Fill in the table below using
whichever is more appropriate g or mL; specify your units.
Reagent
Na2CO3
moles
(mmol)
7.40
grams or mL
(specify units)
0.82 g
Acetonyltriphenylphosphonium chloride
7.36
2.62 g
Dioxane:
211 (293)
18 mL (25 mL)
Water
Approximately
what temperature will the reaction344
be refluxing?
6.2 mL
8
1 point each box. 2 2.0 g = 6.89 mmol. Procedure in Journal Experimental is for 14.9 mmol so
scale everything by (0.41). Dioxane:H2O 3:1
CHEM 216H
Exam 1, 2005
Page 2
d) Draw the reaction set up for the transformation of 2 to 3. Include all necessary glassware, means
of mixing and heating/cooling. Label all of the components.
8
e) At approximately what temperature will the reflux take place?
100-102o C
1
f) There is a mistake in one of the following sentences from the experimental:
“Upon cooling to room temperature, the solvents were evaporated, and the residue was taken up in
150 mL of EtOAc. After the addition of 50 mL of 1 M NaHSO4, the mixture was partitioned in a
separatory funnel. The aqueous layer was then washed with 1 M NaHSO4 and brine, dried, and
filtered. The organic extract was then concentrated in vacuo, and the yellow flakey residue was taken
up in 80 mL of hexanes with a very small amount of EtOAc (ca 4-5 mL).”
Rewrite the incorrect sentence to make the experimental correct:
The organic layer was then washed with 1 M NaHSO4 and brine, dried and filtered.
4
CHEM 216H
Exam 1, 2005
Page 3
g) “Upon cooling to room temperature, the solvents were evaporated, and the residue was taken up in
150 mL of EtOAc. After the addition of 50 mL of 1 M NaHSO4, the mixture was partitioned in a
separatory funnel.” Is the layer on top or on bottom greater in volume? Explain.
Top: EtOAc 150 mL density 0.902 g/mL
Bottom: 1 M NHSO4 50 mL assume density is same as that of water: 0.997 g/mL
3
h) What would you recommend for use in drying the organic layer?
Anhydrous Na2SO4, MgSO4
1
i) After drying, why was the organic layer subsequently filtered?
To remove the solid drying agent that has absorbed the water.
2
j) Why was the double bond in the product 3 assigned as trans? Use experimental evidence to make
your case.
The peak at 6.07 ppm d J= 16.0 Hz, 1H has a high value (16Hz) for its coupling constant indicating
that it is a trans coupling. A cis double bond would have a coupling constant in the range of 6-15 Hz.
H
CH3
....
H
O
3
CHEM 216H
Exam 1, 2005
Page 4
II. (22 points) Compound 12a comes from a paper in the Journal of Organic Chemistry (JOC
2005, 756). Assign the reported characterization data to specific site in the molecule.
a) IR (liquid film): 2102, 1607, 1495,
1241, 1161, 1039, 914, 811. Circle the
functional groups responsible for the IR
stretches at 2102 and 1607 cm-1. Label
each circle with the appropriate wave
number.
4
2102
1607
H3CO
12a
b) Fill in the table below with the letters a-j to assign the 1H NMR (CDCl3, 300 MHz) spectrum. More
than one letter may go in each box.
9
Integration
δ
7.42
1H
6.75-6.68 2H
5.88
1H
Multiplicity
J (Hz)
d
m
ddt
5.07
5.02-4.98
3.81
3.19
2.88
2.46-2.37
dd
m
s
s
t
m
c
b, d
17.0, 10.3, g
6.5
17.0, 1.7
h
i
a
j
7.8
e
f
1H
1H
3H
1H
2H
2H
c
Assignment
8.2
b
Assignment
l
146.0 m, n, o,
137.8 r
134.0
114.8, w, u, v
114.4
113.6
111.2
δ
82.3
79.3
Assignment
p,q
a
H3CO
H
H
e
d
J
J
h
g
h
i
H
H
i
g
= 17.0 Hz
= 1.7 Hz
4
d) Assign the 13C NMR spectrum, by filling the letters kw in the table on the left. More than one letter may go in
each box.
n
55.3
m
H3CO
k
l
w
5
q
p
o
r
s, t
C
H2
j
h
H2
C
k
34.6
34.3
H
f
c) Coupling constants are usually listed in the form Jxy = 7 Hz
where x and y are letters representing the H atoms involved in
the coupling. For the peak at 5.07 ppm (dd), fill the letters of
the hydrogens involved in the couplings in the box to the right.
δ
159.6
H
H
s
C
H2
H2
C
t
v
u
CHEM 216H
Exam 1, 2005
Page 5
III. (24 points): You find three compounds (A-C) with the molecular formula C7H12O2. Identify
these compounds using the mass spec, IR, and NMR data provided in the supplemental handout.
Draw each compound in the respective box below.
Compound A
Compound B
O
O
OH
O
8
8
Compound C
O
O
8
CHEM 216H
Exam 1, 2005
Page 6
IV (20 points) How will each of the following characterization techniques help you to differentiate
between the starting material D and the product E in the following transformations? Briefly
describe in a single glance what one thing would allow you tell the difference.
H
OH
D
O
E
UV-vis
E will have a higher λmax due to the π → π* and NB → π* electron transitions which are lower in
energy than the σ → σ* and NB → σ* transitions that can take place in D.
4
IR
D OH 3600-2500 cm-1 broad; no C=O or C(O)H
E C=O 1750-1650 cm-1 intense
C(O)H stretch 2900 and 2700 cm-1
No OH
4
Mass spec
D molecular ion C4H10O 74
E molecular ion C4H8O 72
3
4
1
H NMR
A) D OH broad singlet 1-5 ppm; E C(O)H singlet 9.5-10 ppm
B) D CH2OH 2H triplet at ~4 ppm; E CH2C(O)H 2 H triplet ~2.5 ppm
C) D 3 methylene peaks; E 2 methylene peaks
4
13
C NMR (no 1H coupling)
E C=O 177-185 ppm (170-220)
D no peak further downfield than ~65 ppm
4