CHEM 112B
Spring 2014
Instructor: Felix Fischer
Midterm Examination I Answer Key
Thursday, February 20, 2014
Name:
__________________________________
Student ID:
__________________________________
GSI:
__________________________________
(1)
16 points
(2)
16 points
(3)
20 points
(4)
16 points
(5)
12 points
(6)
10 points
(7)
10 points
Total
100 points
YOUR EXAM SHOULD HAVE 17 PAGES
NOTE 1: PLEASE START BY WRITING YOUR NAME AND STUDENT ID ON THE
COVER PAGE AND YOUR INITIALS ON THE TOP RIGHT OF EACH OF THE OTHER
PAGES.
NOTE 2: PLEASE WRITE ALL ANSWERS IN THE SPACES PROVIDED. ONLY
THESE WILL BE GRADED. IF YOU NEED MORE SPACE USE THE THREE
SCRATCH PAPERS PROVIDED ON PAGE 15-17.
NOTE 3: PLEASE WRITE AND DRAW CLEARLY.
CHEM 112B
Spring 2014
Initials: _______________
1) (16 points) Draw the major 1,2- and 1,4-addition products of the following reactions?
For each reaction indicate the kinetic and the thermodynamic products.
(a)
Cl
HCl
Cl
H
H
kinetic
thermodynamic
(b)
Cl
Cl
Cl
Cl
Cl 2
kinetic
thermodynamic
(c)
H
H
Cl
HCl
Cl
kinetic
thermodynamic
(d)
H
H
HBr
Br
kinetic
2
Br
thermodynamic
CHEM 112B
Spring 2014
Initials: _______________
2) (16 points) Suggest a reaction mechanism for each of the following reactions that
accounts for both products. Use clear arrow pushing and draw all intermediates, and
resonance structures. Indicate the minor and major product.
(a)
H 2O, acetone
Cl
OH
+
reflux
OH
+
Cl
O
H
H
H
O
H
H
O
H
-H
OH
-H
HO
minor
major
H
O
3
H
HCl
CHEM 112B
Spring 2014
Initials: _______________
(b)
Br
HO
HBr, H 2SO 4
C
HO
C
60 °C
Br
H
H O
H
C
C
-H2O
C
C
Br
Br
1pt
Br
C
Br
major
minor
+
4
CHEM 112B
Spring 2014
Initials: _______________
3) (20 points) Draw all the products formed in the following Diels-Alder reactions. Clearly
indicate the stereochemistry in the products. If a racemic mixture of products is formed
you only need to draw one enantiomer. Indicate the racemic mixture with a “(+/–)” sign.
(a)
CH3
H
CN Diels-Alder
+
CH3
H
CN
CH3
CH3
CN
CN
CN
CN
CH3
CH3
5
CHEM 112B
Spring 2014
Initials: _______________
(b)
O
Diels-Alder
+
O
O
H
H
H
H
6
CHEM 112B
Spring 2014
Initials: _______________
(c)
Br
+
O
KNH 2
O
C11H10 O
O
7
CHEM 112B
Spring 2014
Initials: _______________
(d)
S
Diels-Alder
a bicyclic product
Et
O
H
H
H
H
SEt
O
O
H
H
H
H
SEt
O
O
exo products not required for credit
SEt
8
SEt
CHEM 112B
Spring 2014
Initials: _______________
4) (16 points) Using the Hückel rules determine whether each of the following
compounds is aromatic, antiaromatic, or non-aromatic.
Explain your choice in less than 20 words.
(a)
NO 2
aromatic
planar
conjugated
O
6π→4n+2π
(b)
non-aromatic
planar
N
not conjugated: N atom is sp3 hybridized
4nπ antiaromaticity avoided
(c)
aromatic
planar
conjugated
6π→4n+2π
(d)
aromatic
N
planar
S
conjugated
6π→4n+2π
9
CHEM 112B
Spring 2014
Initials: _______________
5) (12 points) Predict the major products of the following reactions.
(a)
H 2SO 4
SMe
2 major monosubstitution products
HNO 3
SMe
SMe
O 2N
NO 2
(b)
N
O
AlCl3
Cl
CH 2Cl 2
+
O
N
O
O
10
1 major product
CHEM 112B
Spring 2014
Initials: _______________
(c)
OH
H 2SO 4
2 products resulting from
electrophilic aromatic substitutions
11
CHEM 112B
Spring 2014
Initials: _______________
6) (10 points) Identify the products of the following reactions. Draw a detailed curved
arrow mechanism that leads to the major product. Clearly indicate resonance structures,
and charges in the intermediates
(a)
Cl
Product:
NO 2
H 3C
CH3NH 2
NH
NO 2
Br
Br
Mechanism:
H H
H 3C N Cl
Cl
H 2N CH3
NO 2
Br
NO 2
Br
-H
H 3C NH Cl O
N
H 3C NH Cl
O
Br
NO 2
H 3C NH Cl
Br
Br
-Cl
H 3C
NH
NO 2
Br
NO 2
12
H 3C NH Cl
NO 2
Br
CHEM 112B
Spring 2014
Initials: _______________
(b)
O
Product:
HO
CH3SO3H *
or
Mechanism:
H
O
O
H
O
H
HO
HO
HO
HO
H
H
H
H
HO
H
HO
HO
-H
H
H
H O
-H2O
-H
H
H
hint: * is a strong acid that is soluble in organic solvents
13
CHEM 112B
Spring 2014
Initials: _______________
7) (10 points) Propose a reasonable synthesis of 3-ethylbenzonitrile starting from
benzene and any other inorganic or organic reagent with two or less carbon atoms.
CN
3-ethylbenzonitrile
O
HNO 3
H 2SO 4
Cl
NO 2
AlCl3
O
amine reduction
NH 2
O
ketone reduction
NH 2
O
HONO
H 2SO 4
N
N
CuCN
HSO 4
14
CN
CHEM 112B
Spring 2014
Initials: _______________
Scratch Paper:
15
CHEM 112B
Spring 2014
Initials: _______________
Scratch Paper:
16
CHEM 112B
Spring 2014
Initials: _______________
Scratch Paper:
17