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TA Name:
Hour Exam #3
5.13 Fall 2006
KEY
Organic Chemistry II
November 15, 2006
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1.
Make sure your exam has 9 numbered pages plus a periodic table.
2.
Write your initials on each page.
3.
Look over the entire exam before you begin to familiarize yourself with its
length. Do what you know first, then attempt the harder problems.
4.
Show all of your work. Partial credit receives points!
1. (4 pts) When N,N-dimethylaminopyridine reacts with one equivalent of acid,
the sp2 nitrogen becomes protonated.Why don't you see protonation at the sp3
nitrogen when you know that the more p character an orbital has, the more stable
it is with a positive charge?
H
H3C N CH3
H3C
N
CH3
H3C
H+
N
CH3
H+
N
N
N
H
conjugate acid
not formed
The Sp3 Nitrogen is actually Sp2. The lone pair on nitrogen is in a P orbital
&can delocalize into the pyridine ring. The lone pair of electrons on the Nitrogen
atom in the ring are orthogonal to the ring & cannot delocalize .Those electrons
are more available for bonding and more basic.
2. (4 pts) Rank the following molecules in order of electrophilicty(1= most electrophilic )
O
CH3
Me
N
CH3
4
O
Me
O
Cl
1
Me
S
2
CH3
O
Me
O
CH3
3
Figure by MIT OCW.
3. (18 pts) Provide the missing products for each reaction. Indicate no reaction with N.R.
H3C
(a)
(b)
CH3
N
CH3
H3C
CH3
O
H3C
NH2
H2O2
D
NaBH4
NR
1.CH3l(excess)
2.Ag2O
3. D
CH3 1.CH3l(excess)
2.Ag2O
3. D
N
(c)
H3C
(d)
O
H3C
(e) H3C
H
O
Cl
+ HNMe2
+
NaBH3CN
H+
1. HNMe2,pyridine
2.LiAlH4
3. H2O
N
+
:N(Me)3
CH3
Me
N
H3C
Me
H
N
H3C
CH3
CH3
2
Figure by MIT OCW.
4. (21 pts) Provide the missing reagents for each reaction. Several steps may be needed for
some transformations.
1.LiAlH4
2. H2O
(a) H C C N
3
H 3C
(b)
H3C
H 3C
H
Pr
HO
OEt
1. H3O+/H2O, D
2. EtLi (2 eq.)
O
(d)
H 3C
MeMgBr
2 eq.
Pr
Me
Me
1.H2N OH,H+
2. LiAlH4
3. H2O
O
NH2
CH3
H3C
or 1. POCl3 2.EtMgBr
NH2
H3C
CH3
3. H3O+/H2O
1.SOCl2
2. NH3
3. NaOH, Br2
O
1.LiAlH4
2. PCC
O
OH
O
(c)
or
1. SOCl2
2.LiAl(OtBu)3H
O
NH2
NH2
OH
(e)
1. NaN3
(f)
H3C
Br
2. LiAlH4
3. H2O
or
1.
2.
O
N K
H2N
NH2
H3C
+
O
NH2
Figure by MIT OCW.
3
(1 2 pts) Consider the labeling experiment outlined below. What level of 18O
incorporation do you expect in the recovered anhydride (high or low)? Your
answer should include a mechanism of hydrolysis and a detailed explanation.
5.
O
O
O
Me
O
O
O
+
Me
k1
OH
*
stop at 50% conversion
of acetic anhydride
*
OH/H
*
2O
O
*
OH
O
Pt
O
k-1
O
O
O
+
k-1
O
O
*
O
k1
k2
k2
O
O
*
O
HO
O
*
OH
*
OH
+
O
O
O
18
O Incorporation is expected to be low in recovered anhydride.
O
OH. There fore, k2 >> k-1, or elimination of
O
is a better leaving group than
faster than revesal to starting material. Most of the
O
18
O will be found in the acetic acid product.
Figure by MIT OCW.
4
6. (10 pts) Provide a mechanism for the following transformation.
O
MeO
O
MeO
Me
+
OH
Me
O+/H
OH H3
2O
Me
O
Me
Me
O H
H OH2
MeO
Me
Me
O
Me
OH
Me
MeO
MeO H
OH
Me
PT
OH
O
O
H
Me
Me
O H
Me
+ OH2
O
OH2
Me
O
O
+ H3O
Me
Me
Figure by MIT OCW.
5
(10 pts) Under basic hydrolysis conditions, a nitrile goes through a primary
amide intermediate before becoming a carboxylate. Show the mechanism for this
reaction and explain why it is NOT a facile method for converting nitriles into
carboxylates.
7.
R
R
C
C
N
-
R
O
+ NH3
N H
N
N
R
OH
C
+
H OH
R
O
H
+
OH
OH
N H
O
R
O
OH/H2O
HO
H
N H
NH2
R
R
O
O
HO
O
R
OH
NH2
O
O
R
O
H
NH2
+
R
O
+ NH3
Base catalyzed hydydrolysis of nitriles is not a facile process because NH2
is not good leaving group( -OH is better!) There, fore, the reaction is slow.
Figure by MIT OCW.
6
8. (9 pts) Provide a synthesis for the following compound.
OH
Cl
HNO3
NO2
H2SO4
NO2
Cl2
AlCl3
Cl
H2, Pd
OH
Cl
H2SO4
N N
NH2
NaNO2
HCl
Cl
Cl
Cl
Figure by MIT OCW.
7
9. (12 pts) Provide a selective synthesis for ONE of the following compounds. Circle the
molecule that you want graded. All of the carbon atoms of the product should come from
either ethanol or compounds that contain just one carbon atom.
A
B
O
Me
N Me
Me
OH
Me
NH2
B
OH
Mg
PBr3
0
MgBr
Br
OH
1. CO2
2. H2O
O
SOCl2
Cl
LiAl(OtBu)3H
H
HCN
CN
O
O
OH
1. LiAlH4
2. H2O
OH
NH2
O
OR
1. H
MgBr
H
OH
O
2. H2O
O
OR
Jones
OH
A
O
O
MeOH
EtOH
H
PCC
PBr3
PBr3
EtBr
MeBr
1. NaN3
2. LiAlH4
3. H2O
OR
MeOH
PBr3
MeBr
SOCl2
OH
1. Mg
2. CO2
3. H2O
0
Et
1. NaN3
2. LiAlH4
3. H2O
OH
SOCl2
Cl
O
pyridine
N
O
NH2
1. H
H ,H+
2. LiAlH4
3. H2O
N
H
O
Me
NH2 +
Cl
8
pyridine
H
1. LiAlH4
N
O
2. H2O
H
N
Figure by MIT OCW.
8
EXTRA CREDIT
(5 pts) Synthesize methamphetamine (crystal meth) from benzene and any other reagents.
All the carbon atoms in the product should come from reagents that only contain one
carbon atom.
H
N
Me
1. Mg
2.CO2
Br2
FeBr3
Me
O
OH
3.H2O
1.LiAlH4
OH
2.H2O
PBr3
OH
O
1.MeLi
OH
O
2.H2O
1. Mg
2.CO2
3.H2O
Br
H2NMe
H
+
OH
N
1.LiAlH4
2.H2O
H
N
Figure by MIT OCW.
9