Chem 216, S07 E2
Name_____KEY____________________
Page 1
I. (14 points) The Grignard reagent C6H5-MgBr is prepared from bromobenzene (C6H5-Br) and
Mg. Answer in the boxes below the following questions.
(1) (2 points) Is the carbon atom associated with the bromine atom in bromobenzene electrophilic or
nucleophilic?
electrophilic
nucleohpilic
[circle one]
(2) (2 points) Is the carbon atom associated with magnesium in the Grignard reagent electrophilic or
nucleophilic?
electrophilic
nucleohpilic
[circle one]
(3) (2 points) Is the magnesium atom oxidized or reduced during the formation of the Grignard
reagent?
oxidized
reduced
[circle one]
(4) (4 points) Explain why the Grignard reaction has to be carried out in an anhydrous solvent.
Because the Grignard reagent formed would be destroyed by its reaction
with water present in a non-anhydrous solvent.
(5) (4 points) Write the conjugate carbon acid (i.e., C-H) of the C6H5–MgBr and explain why
Grignard reagents are strong bases.
structure:
explanation:
The pKa value of benzene H is
extremely high (around 45). Therefore, its
conjugate base is strongly basic.
II. (6 points) Acetaldehyde [CH3C(=O)H] sometimes is present in technical-grade diethyl ether. If
this grade of diethyl ether were used, what effect, if any, would the acetaldehyde have on a
Grignard reagent used? Explain through the use of a chemical equation using C6H5–MgBr as an
example.
explanation based upon the reaction mechansim:
The Grignard reagent formed would be destroyed by its reaction with acetaldehyde.
H
O
BrMg
H3C
BrMg
O
H3C
H
Chem 216, S07 E2
Name_____KEY____________________
Page 2
III. (14 points) For the reaction below, draw in the box provided the structure of the expected
major product and propose a step-wise mechanism for its formation using the curved-arrow
convention. Make sure not to combine more than one mechanistic steps.
O
O
O-Na+
HO
O
CH3
CH3
NaOH (1.1 mol equiv)
H2O, !
H3CO
+ enantiomer
H3CO
4
Na salt
Mechanism:
O
Na
O
O
O
OH
CH3
OH
H
CH3
O
H
Na
H3CO
O
O
OH
CH3
Na
H3CO
H
H3CO
O
HO
OH
O
O
CH3
O
CH3
HO
H3CO
Na
H3CO
10
IV (14 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.
(1)
-O
(2)
NH3+ CH3
2C
H3C
CH3
O
O
O
6
CH3
OH
OH
4
(5)
H
H3C
O
H3C
O
H3C
O
H3C
O
6
5
(7) H C
3
(6)
O
N
N+
CH3 I-
6
(4)
(3)
O
OH
4
H3C
at room temperature
CH3
6
Chem 216, S07 E2
Name_____KEY____________________
Page 3
V. (12 points) For each of the following Diels-Alder reactions, provide in the boxes given the
expected major products. Make sure to indicate stereochemistry of the products.
(1)
O
O
H3C
O
O
O
O
+
CH3
!
O
O
H
H O
O
O
O
O
H O
H
4
endo-product
(2)
CN
NC
NC
CN
!
+
4
+ enantiomer
(3) [Org. Lett. 2007, 9, 517]
O
O
O
+
O
H
O
benzene
100 °C
H
H
O
O
O
H
O
O
H
H
O
O
4
endo-product
VI. (4 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 6, 6, and 9 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 =
6
3
:
6
2
:
9
6
2 : 3 : 1.5
4
:
6
:
3
Chem 216, S07 E2
Name_____KEY____________________
Page 7
VIII. (continued)
(1) (1 points) What is(are) the unit(s) of unsaturation of this compound?
____0________
(2) (2 points) What does the IR spectrum tell you in terms of the
N-containing functional group in this molecule?
____NH2_____
(3) (1 points) How many groups of chemically equivalent carbons
does this compound have?
_____4_______
(4) (1 points) How many methyl groups does this
compound have?
____2_______
(5) (3 points) What is the structure of this compound?
NH2
H3C
CH3
3
(6) (6 points) Assign all 1H and 13C chemical shifts to the structure. Note: This compound may
have a pair of diastereotopic Hs. However, these Hs might have virtually identical chemical
shifts.
2.8 ppm (sextet)
32.5 ppm (C)
NH2 1.67 ppm (broad singlet)
H
10.4 ppm (C)
H3C
0.9 ppm
(triplet)
C
C
H
H
48.2 ppm (C)
CH3
1.05 ppm (doublet)
23.1 ppm (C)
1.35 ppm
(apparent quintet)
6
Chem 216, S07 E2
Name_____KEY____________________
Page 9
IX. (continued)
(1) (1 points) What is(are) the unit(s) of unsaturation of this compound?
_____3______
(2) (3 points) What do the IR and C-13 NMR spectra tell you in terms of the
N-containing functional group in this molecule?
_cyano (or nitrile) group____
(3) (1 points) How many groups of chemically equivalent carbons
does this compound have?
___5_________
(4) (1 points) How many methylene carbon peaks does this
compound have?
___2_________
(5) (3 points) What is the structure of this compound?
H3C
O
C
O
N
3
(6) (6 points) Assign all 1H and 13C chemical shifts to the structure.
164 ppm (C)
3.4 ppm (singlet)
62 ppm (C)
1.2 ppm (triplet)
H3C
12 ppm (C)
H
H
O
C
H
H
114 ppm (C)
C
C
C
O
N
24 ppm (C)
4.2 ppm (quartet)
6
Chem 216, S07 E2
Name_____KEY____________________
Page 11
X. (continued)
(1) (1 points) What is(are) the unit(s) of unsaturation of this compound?
____4________
(2) (2 points) What does the IR spectrum tell you in terms of the
O-containing functional group in this molecule?
____OH______
(3) (1 points) How many groups of chemically equivalent carbons
does this compound have?
_____7_______
(4) (1 points) How many sp2 carbon peaks does this
compound have?
_____6_______
(5) (3 points) What is the structure of this compound?
CH3
OH
3
(6) (6 points) Assign all 1H NMR peaks to the structure.
6.74 ppm (doublet)
H
7.10 ppm (triplet) H
H
6.62 ppm (doublet)
CH3
2.3 ppm (singlet)
H
6.65 ppm (singlet)
O
H
5.4 ppm (singlet)
6