The Grignard reagent produced would be destroyed by the reaction

216 S11-E2 Page 2
Name ________Key______________
I. (9 points) Answer in the boxes below the following questions for the Grignard reagent CH3-MgBr.
(1) (2 points) Is the carbon atom associated with magnesium electrophilic or nucleophilic?
electrophilic
nucleophilic
[circle one]
(2) (3 points) Explain why the Grignard reaction has to be carried out in an anhydrous solvent.
The Grignard reagent produced would be destroyed by the
reaction with water present in a non-anhydrous solvent.
(3) (4 points) Write the conjugate carbon acid (i.e., C-H) of the CH3– MgBr and explain why Grignard
reagents are strong bases.
structure:
H
H C H
H
explanation:
The pKa of CH4 is ca. 50. Therefore,
its conjugate base is highly basic.
II. (6 points) Ethyl alcohol (C2H5OH) 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 used? Explain using a chemical equation using methylmagnesium bromide as an example.
explanation based upon the reaction mechansim:
A Grignard reagent formed would deprotonate H of the ethyl alcohol OH.
H
R
OCH2CH3
R H
MgBr
+
BrMg OCH2CH3
III. (8 points) For each of the reactions below, draw in the boxes provided the structure of the
expected major organic product.
(1)
OH
1. Mg (1.1 mol equiv)
ether
Br
2.
H3C
aq NH4Cl
(acidic workup)
CH3
O
(1.1 mol equiv)
4
+ enantiomer
(2)
Mg (1.1 mol equiv)
ether
Br
aq NH4Cl
(acidic workup)
OH
CH3
O
MgBr
O
4
+ enantiomer
216 S11-E2 Page 3
Name _______Key_______________
IV. (16 points) For the following reaction sequence, draw the correct structures in the boxes provided.
+
Ph3P:
CH3
Br
(C18H15P)
benzene, reflux
O
CH3
Ph3P
Br
O
4
"salt"
trans
H
H
O
NaOC2H5 /C2H5OH
CH3
H
H
4
major isomer: C12H12O
+
H
H
O
H
O
O
dichloromethane
room temperature
H
CH3
Ph3P
H
cis
H
H
4
C21H19PO (ylide)
+ NaBr + C2H5OH
CH3
4
minor isomer: C12H12O
+
note: Ph = C6H5
Ph3P=O
V (12 points) Show how many peaks you would expect to observe in the proton-decoupled 13C NMR
spectrum of each of the following compounds. Indicate your answers in the boxes provided.
O
(1)
(2)
CH3
H3C
-OOC
chiral center!
O
(3)
S
S
NH3+
HO
7
6
(4)
COOH
(5)
7
(6) H3C
COOH
180°
rotation
cis
CO2H
CO2H
CH3
COOH
6
COOH
5
O
CH3
O
CH3
O
H3C
5
216 S11-E2 Page 4
Name ________Key_____________
VI. (5 points) The proton NMR spectrum of a mixture of acetonitrile (CH3C≡N), methylene chloride,
(CH2Cl2) and benzene (C6H6) is integrated and results in step heights of 15, 6, and 18 mm for the
signals at δ 2.10, 5.30, and 7.26 ppm, respectively. In what mole ratio are the three substances present?
No explanation required. No partial credit will be given to this problem.
acetonitrile : methylene chloride : benzene =
15
:
3
6
2
:
5
18
:
6
:
3
3
VII. (8 points) For each of the reactions given below, draw in the box the structure of the expected
product. Make sure to indicate the stereochemistry of the product whenever applicable.
(1)
O
OCH3
+
O
H
CH3O
CH2Cl2
(solvent)
H
O
+ enantiomer
O
room temperature
H
O
O
endo product
(2)
H
H
O
H
+
O
CH2Cl2
(solvent)
H
room temperature
H 3C
4
CH3
+ enantiomer
H
CH3
H
or
HO
endo product
4
VIII. (10 points) Provide in the box below a step-by-step, curved-arrow mechanism for the formation
of hydroxy acid 2 from diketone 1. Make sure to include the mechanism for the acidic workup as well.
O
O
mixture of stereoisomers here
KOH ( 4 mol equiv)
H2O
H3O+
reflux
to pH = 1.0
OH
OH
1
2
mech arrows: 1 pt
O
O
O
1
O
O
mech arrows: 1 pt
interm str: 1 pt each
2
H
mech arrows: 1 pt
OH
O
O
1
H
H O
O
OH
OH
This is fine, too.
O
O mech arrows: 2 pts
O
O
OH
H
O mech arrows: 1 pt
O
OH
H
O
H
O
H
216 S11-E2 Page 5
Name ________Key_____________
216 S11-E2 Page 6.
Name __________________________
IX. (continued)
O
A
O
C
O
O
E
O
B
D
O
F
G
Br
O
H
O
O
O
X. (15 points) On the basis of its spectroscopic information provided below, propose the structure for
the compound, C5H12O. Draw the proposed structure in the box on page 7 and give a brief explanation
as to how the structure is deduced from the spectroscopic information provided.
Structure:
H
H3C
H
C
C
H3C
OH
CH3
chiral center!
diastereotopic
methyls
5
0 unit of unsaturation
Explanation (just assign the IR peak at 3368 cm-1 and all H-1 peaks right next to the
corresponding functional group/H-1 nuclei):
3.55 ppm
(multiplet)
3368 cm-1
H
H3C
0.92 ppm
(doublet)
0.88 ppm
(doublet)
H
H3C
C
C
O
CH3
H
1.92 ppm
1.3 ppm (doublet)
1.6 ppm
(octet)
10
216 S11-E2 Page 8
Name ________Key_____________
XI. (15 points) On the basis of its spectroscopic information provided below, propose the structure of
the compound, C10H16O4. Draw the proposed structure in the box on page 9 and give a brief
explanation as to how the structure is deduced from the spectroscopic information provided. Make
sure to assign all proton and C-13 NMR peaks.
216 S11-E2 Page 9
Name ________Key_____________
XI.
(continued)
Structure:
H 3C
H 3C
CH3
CH3CH2O
O
OCH2CH3
O O
OCH2CH3
O
CH3CH2O
H 3C
OCH2CH3
CH3
H3C
O
OCH2CH3
O
These should show only one sp2
alkene C-13 peak. => -1 point
5
Explanation (just assign the strongest IR peak and all H-1 and C-13 peaks right next to the
corresponding functional group/H-1, C-13 nuclei): Units of unsaturation: 3; only 6 C-13 peaks!
2.0 ppm
H 3C
1725 cm-1
4.2
125 ppm
ppm 14 ppm
156
O
ppm
1.2 ppm
OCH2CH3
22 ppm
60 ppm
H 3C
2.0 ppm
OCH2CH3
O
1725 cm-1 167
ppm
14 ppm
4.2 ppm
10