216 F09-Exam #2 Page 2.
Name _____Key______________
I. (6 points) There are two types of filtration methods used in organic experiments. These are: (i) gravity
filtration using a short-stemmed (glass filter) funnel and fluted filter paper and (ii) vacuum (or suction)
filtration using, e.g., a Hirsch funnel and round filter paper to cover the inside bottom of the funnel. For
each of the following experimental operations, suggest which of the two filtration methods should be
used.
(1) A step to remove insoluble impurities from a solution of a compound in hot solvent in the process of
recrystallization of the compound:
___gravity filtration__________________
(2) A step to collect crystals obtained by cooling down the filtered hot solution (see above) of a
compound to room temperature:
___suction filtration__________________
(3) A step to collect precipitates formed upon addition of aqueous HCl to the solution of the sodium salt
of dilantin (Experiment 6):
___suction filtration__________________
II. (9 points) In a number of experiments you performed in the lab, the product mixtures were extracted
with diethyl ether a few times. The combined organic layers were first washed with water and then with
brine. The resulting organic solution then was dried over a drying agent such as anhydrous CaCl2,
Na2SO4, and MgSO4. Answer in the boxes provided the following questions.
(1) (3 points) What is brine?
saturated aqueous NaCl solution
(2) (3 points) What is the purpose of this washing with brine?
To reduce the amount of water dissolved in (diethyl) ether.
(3) (3 points) Explain the chemical basis for the use of a drying agent? Use MgSO4 as an example. Be
specific if any chemical process is involved.
MgSO4 + 7 H2O
MgSO4 7H2O
III. (5 points) Ethyl alcohol [CH3CH2OH] quite often is present in technical-grade diethyl ether. If this
grade of diethyl ether were used, what effect, if any, would the ethyl alcohol have on a Grignard reagent
produced? Explain in the box below using words and a chemical equation with phenylmagnesium
bromide [C6H5MgBr] as an example. You need not show the mechanism for this process.
MgBr
+
H-O-CH2CH3
+
BrMg-O-CH2CH3
is a strong base (the pK a of its conjugate acid is around 40) and it deprotonates
an acidic hydrogen of the HO of ethanol.
216 F09-Exam #2 Page 3.
Name______ Key _______________
IV. (16 points) For each of the reactions given below, complete the reaction scheme by drawing in each
of the boxes the structure of the expected product. Note: Ph = C6H5
(1)
O
O
O
OCH3
H +
Ph3P
OCH3
CH2Cl2
(solvent)
H
Ph
Ph P O
Ph
+
2
3
phosphorus-containing
product
(2)
H
O
O
N
H
O
H
O
Ph
+ Ph3P
OCH2CH3
O
OCH3
40 °C
THF
(solvent)
CH3
O
CH3
O
O
N
H
Ph
2
O
3
1.
(3)
O
phosphorus-containing
product
MgBr
(2 mol equiv)
diethyl ether (solvent)
O
Ph
Ph P O
Ph
+
2. H3O+ work-up
HO
+
HO
C6H6O
4
no point for
2
O
V. (6 points) Provide in the box below the structure of the necessary reagent to achieve the following
transformation shown, by the use of a Wittig reaction.
(1)
O
O
H
+
O
Ph3P
O
O
3
(2)
O
O
H
+
O
Ph3P
O
O
3
acceptable:
1.
O
Ph3P
H
2.
Ph3P
O
O
216 F09-Exam #2 Page 4.
Name_________ Key ____________
VI. (10 points) Treatment of diketone 1 with CH3ONa in methanol produced a rearranged product. The
IR of the rearranged product indicates the presence of a hydroxyl group and an ester group. Draw in the
box below the structure of this rearranged hydroxy ester product. You do not need to show the
stereochemistry of the product.
N
N
N
O
CH3OH (solvent)
reflux, 6 h
O
HO
O
1
O
O
CH3ONa
N
OCH3
or O here
4
Provide in the box below a reasonable step-by-step mechanism that accounts for the formation of this
product.
Mechanism (use an abbreviated structue of 1 as shown in the box):
N
O
O
N
N
CH3OH
Na
O
1
OCH3
1 pt for arrows
N
O
N
N
O
1 pt for the structure
O
O
OCH3
O
2 pts for arrows
2 pts for the structure
OCH3
O
N
H
O
N
OCH3
2 pts for the structure
HO
OCH3
O
An alternative mechanism that starts with the addition of OCH3
to the other C=O carbon is acceptable.
6
VII. (8 points) Show how many peaks you would expect to observe in the proton-decoupled 13C NMR
spectra of each of the following compounds. Indicate your answers in the box provided. Do not count the
13
C NMR peaks of the solvent and TMS.
(1)
(2)
H3C
CH3 NH3
chiral center!
6
H3C
O
N
CH3
H3C
(room temperature)
O
6
O
CH3
O
O
H3C
(4)
(3)
6
6
216 F09-Exam #2 Page 5.
Name _____ Key _______________
VIII. (20 points) Fill in the boxes in the following statement.
In the proton NMR spectrum of ethyl bromide [CH3CH2Br], the chemical shifts of the methyl hydrogens
and the methylene hydrogens are δ = 1.72 and 3.25 ppm, respectively, and the coupling constants
between these groups of hydrogens are 7 Hz. The number of peaks given by the methyl hydrogens is
3 . These methyl hydrogen peaks are separated from each other by
ratio, from the most down field peak to the most upfield peak is
given by the methylene hydrogens is
other by
peak is
1 : 2 : 1
. The number of peaks
4 . These methylene hydrogen peaks are separated from each
7 Hz and their approximate area ratio from the most down field peak to the most upfield
1 : 3 : 3 :1
. The total area of the methyl hydrogen peaks compared with that of the
3 : 2
methylene hydrogen peaks is in the ratio of
groups of peaks of 1.53 ppm corresponds to
612
. Of these two groups of peaks, the
hydrogen peaks are farther downfield. The chemical shift difference between these
methylene
to
7 Hz and their peak area
306
-Hz difference on a 200 MHz instrument and
-Hz difference on a 400 MHz instrument.
IX. (14 points) Consider the chemical equivalency of the hydrogen atoms in the following compounds.
(1) Identify the indicated pairs of hydrogens as (H) homotopic, (E) enantiotopic, or (D) diastereotopic Hs.
Write the answers as (H), (E), or (D).
(2) How many unique (or discrete) hydrogens are there in each of the two compounds? Write the number
of unique (or discrete) hydrogens present in each of the following two compounds.
(a)
H
Ha
Hb
H
OCH3
H
OCH3
H
Hc
E
Ha and Hb _______
3
Number of unique (or discrete) hydrogens: ________
(2 points)
E
Ha and Hc _______
H
Ha and Hd _______
Hd
3
(b)
H
Ha
Hb
H
OH
H
H
H
Hc
Hd
D
Ha and Hb _______
D
Hc and Hd _______
E
Ha and Hc _______
D
Hb and Hc _______
D
Ha and Hd _______
E
Hb and Hd _______
6
Number of unique (or discrete)
hydrogens:
6
_________
(3 points)
216 F09 Exam #2 Page 6.
Name________ Key ____________
X. (11 points) Shown below is the 1H NMR spectrum (at 300 MHz in CDCl3) of a compound whose
molecular formula is C5H12O. The IR spectrum of the compound (liquid film) shows a strong peak in the
3400-3300 cm-1 region.
(1) (1 point) What is (are) the unit(s) of unsaturation of this compound?
_______zero_______
(2) (2 points) What does the IR spectral information tell you in terms of the presence of an O-containing
functional group in this compound?
__hydroxyl group___
(3) (8 points) Draw in the box below the structure of this compound and assign the NMR peaks (by
reading their chemical shifts) to the corresponding H(s).
1.45 ppm
H
H
O
H
0.9 ppm
CH3
CH3
1.3 ppm
H
H
3.7 ppm
Chemical shift assignments: 1 pt each
Structure: 3 points
H
1.7 ppm
216 F09 Exam #2 Page 7.
Name _______ Key ____________
XI. (15 ponts) On the basis of its spectroscopic information provided below, answer the questions given
on page 8 and draw the structure of the compound (C6H12O2) in the box on page 8. In addition, assign all
1
H peaks to the corresponding nuclei.
IR spectrum (liquid film)
216 F09 Exam #2 Page 8.
Name _______ Key _____________
XI. (continued)
13
C NMR spectrum in CDCl3 (proton-decoupled spectrum)
(1) (1 points) What is (are) the unit(s) of unsaturation of this compound?
____one______
(2) (2 points) What does the IR spectrum tell you in terms of the presence
of an O-containing functional group in this molecule?
__carbonyl group__
(3) (2 points) What does the 13C NMR spectrum tell you in terms of the
presence of an O-containing functional group in this molecule?
__ester group_____
(4) (5 points) What is the structure of this compound? (no partial)
O
O
5
(5) (5 points) Assign all 1H shifts to the corresponding H atoms in the proposed structure.
1.35 ppm
H
H
0.9 ppm
H3C
4.0 ppm
H
O
H
O
H
1.6 ppm
CH3
2.0 ppm
H Chemical shift
assignments: 1 pt each
5