midterm iii a key 2321 f13
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Chem 2321-003 Midterm III F‘13
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Chemistry 2321-003
Organic Chemistry I
Midterm Examination III 11:00 am – 12:20 pm
Form A
November 26, 2013
J. Jeon
Name: ________________Key________________ Total /100 please print (last, first)
ID #: ______________________________________
• There are 110 points on this exam and the eight exam pages. • For the multiple choice questions 1-9, select the best answer and darken completely with a
pencil the space corresponding to that answer in scantron (form # 882-E). • Look over entire exam before starting and carefully read all instructions. • You are free to use molecular models during the exam. • For questions 10 and 13, I will not reconsider grades for answers written in pencil.
Have fun!
Chem 2321-003 Midterm III F‘13
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1. (5 pts) These problems are about the IUPAC (International Union of Pure and Applied Chemistry) nomenclature of organic compounds. Select the best name for the following molecule. d)
Me
Me
Me
a) (S)-3-methylhept-4-yne b) (R)-3-methylhept-4-yne c) (S)-5-methylhept-3-yne d) (R)-5-methylhept-3-yne e) (S)-4-methylhept-5-yne
2. (5 pts) Consider the following addition reaction. Which of the following structures is the correct structure of the intermediate B? e) > hydration of alkyne: enol-keto tautomerization
H2SO4HgSO4 (cat.)
H2O
H
A B C
O
Me
a) b) c) d) e)HgSO4 OH
OHOH
3. (5 pts) Predict the major product of the following reaction? b) > ozonolysis of alkenes
1) O3
2) Me2S
HH
Me
Me
a) b) c) d) e)
Me
MeO
Me
MeHOOH
OH
Me
O H
Me
O
Me
MeSMe
Me
Chem 2321-003 Midterm III F‘13
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4. (5 pts) Predict the major product of the following stereospecific reaction? d) > halohydrin
Br2
H2O
a) b) c) d) e)
Br Br Br Br Br HO Br
Br
5. (5 pts) Which of the following bases cannot be used to deprotonate the terminal alkyne A leading to the product B via a carbon-carbon bond formation? a) > basicity [by utilizing either pka values or comparing stabilities of conjugated bases (A.R.I.O.)]
1) base
2)
H
A MeBr
B
Me
e)a) b) c) d)ONa
Me
LiLi allNaN
H
H
(n-BuLi)(PhLi)
6. (5 pts) List the following reactions in order of decreasing rate of reaction? c) > stability of the resulting carbocation intermediates
HBr
ether (solvent) Br
HBr
ether (solvent)MeMeBr
HBr
ether (solvent)MeMeBr
Me Me
I.
II.
III.
a)
b)
c)
d)
e)
I
II
III
II
I
>
>
>
>
=
II
III
II
I
II
>
>
>
>
>
III
I
I
III
III
fastest slowest
Chem 2321-003 Midterm III F‘13
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7. (5 pts) Consider the following reactions (I and II). These two radical reactions produce a mixture of regioisomers (B/C from the reaction I and D/E from the reaction II). The energy diagram of the hydrogen abstraction step in these transformations are shown below, which constitute two individual propagation steps (1. hydrogen abstraction and 2. halogen abstraction):
I.
A
+ Cl2
B
+Cl
C
Cl
ROOR
heatingII.
A
+ Br2
D
+Br
E
Br
+ HCl
+ HBr
ROOR
heating
E
Reaction Coordinate
The hydrogen abstraction step in the chlorination reaction
E
Reaction Coordinate
The hydrogen abstraction stepin the bromination reaction
A
Eac1 Eac2
Eac3
Eac4
A
B1
C1
D1
E1
7. (5 pts) Which of the following statements is true? a)
a) The reaction II is more regioselective.
b) Based on the Hammond postulate the transition state structures of the hydrogen abstraction step in the reaction I more closely resemble intermediates generated during this step.
c) The rate of the reaction II is faster.
d) The activation energy difference (ΔEac) leading to the primary and secondary radical intermediates in the reaction I is larger than one in the reaction II.
e) The entropy of system of the reaction I is negative.
Chem 2321-003 Midterm III F‘13
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8. (5 pts) Of the following molecules, which most readily undergoes a unimolecular elimination reaction (E1)? c) > the rate of the E1 mechanism is rate = k[substrate], so that again the stability of the resulting carbocation intermediates becomes important.
a) b) c) d) e)Br
BrBr Br
Br
9. (5 pts) Of the following covalent bonds, which has the greatest bond dissociation energy? b) > this question asks about which bond is the strongest one.
Hb
Ha
Hc
Hd
Me
a) Ha b) Hb c) Hc d) Hd e) none
10. (10 pts) Draw the major organic product(s) (NO associated mechanism) of the each reaction in the boxes provided. Be sure to indicate stereochemistry if applicable.
Me H2
Lindlar's catalyst(Pd/BaSO4, quinoline)
CH3OH
1) OsO4
2) NaHSO3 H2O
Me
N
quinoline
A
B C
Me
Me
Me
Me OH
OH
Me
Me OH
OH
or
Chem 2321-003 Midterm III F‘13
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11. (15 pts) Consider the following addition reaction.
a) (10 pts) Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) for the following reaction [only step 1) A to B]. Specify the correct regio- and stereochemistry where appropriate. Draw the major product (B) in the box.
b) (5 pts) Draw the major product (C) of the following reaction [B to C] in the box (only product, no mechanism).
●Bonus (5 pts): Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) for the following reaction [only step 2) B to C].
1)
Et 2) H2O2, NaOH
A B C
BH
Et
B
HEt
OH
H
Anti-Markovnikov addition then oxidation (see pages 415 and 475)
Et
B
H
Et
B
H
B
O O HH NaOH
O OH Et
B
H
O OH
see page 415
Chem 2321-003 Midterm III F‘13
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12. (15 pts) Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) for the following reaction. Draw the major product (B) in the box.
NBS (N-Bromosuccinimide)
N
O
O
BrNBS, hv
BA
Hint: During this reaction, small quntities of molecular bromine (Br2) is generated via the reaction below. Utilize
this bromine in the above reaction.
N
O
O
Br + N
OH
O
+ BrH Br Br N
OH
O
+ Br Br NH
O
O
+ Br2
succinimide
BrHH
+ HBr
Br Br
NBS + HBrfrom hint
Br
+ BrH
free radical chain reaction
N
O
O
Brhv
N
O
O
Br+
Chem 2321-003 Midterm III F‘13
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13. (15 pts) Consider the following addition reaction.
a) (10 pts) Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) of the first step [1) Hg(OAc)2, H2O] for the following reaction [A to B] [do not provide the mechanism of the second step, i.e. 2) NaBH4]. Specify the correct stereochemistry where appropriate. Draw the major product (B).
b) (5 pts) Draw the major product (C) of the following reaction [A to C] in the box (only product, no mechanism).
1) Hg(OAc)2, H2O
2) NaBH4
A C
Me
Me
B
H2SO4, H2OMe
Me
MeMe
OH
MeOH
MeMe
Me
Me
Oxymercuration-demercuration technology (A to B) was invented to prevent the inevitable carbocation
rearrangement in an acid-catalyzed hydration reaction (A to C).
MeHg
OAc
MeMeHg
H2OHg
MeH HgOAc
H2O
Hg OAcAcO
OAc
Me Me Me MeMe Me Me Me
OAc
H
OH H OH
2) NaBH4
MeH H
MeMe
OH
no mechanismdiscussion
B
and enantiomers
OH
OH
carbocationrearrangement
minor products(racemic mixture)
nucleophilc attackMajor product
2°
3°
+OH OH
OH
H SO4H
C
A
(a similar question was discussed in our midterm II.)
***** End of Exam ***** You may pick up your exam on Thursday, December 3 (in class). Thank you!