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Chemistry 332
Organic Chemistry II
Exam 5
NH
Cl
Cl
H 3 C
Sertraline (Zoloft
®
) is an antidepressant drug, a selective
serotonin reuptake inhibitor. Compared to Prozac
®
, it has a
shorter duration of action and fewer CNS activating side
effects such as nervousness and anxiety. Zoloft
®
is being
studied as an aid in treating obesity, obsessive-compulsive
disorders, and to depression-prone individuals attempting to
quit smoking.
- Draw the structure of the polymer that results from heating the following diepoxide and diamine (5 points):
O O
O O
H 2 N NH 2
- The polyurethane foam used for home insulation uses methanediphenyldiisocyanate (MDI) as the monomer. Draw the structure of a representative segment of polyurethane prepared by reaction of ethylene glycol with MDI (5 points):
O C N CH 2 N C O + HO^ OH
- Polystyrene is produced commercially by reaction of styrene with n - butyllithium as an anionic initiator. Suggest a reasonable mechanism for this chain reaction. (10 points) H 2 C CH
n
Li CH 2 CH
n
- Which of the following reactions is more likely to occur? Explain. (10 points)
H
H 2
H H
H H
a)
b)
- Identify the pericyclic reaction involved in the following transformation. Use curved arrows to show the electron rearrangement that takes place ( points)
- Dimethylacetylenedicarboxylate (DMAD) reacts with methylenecycloheptatriene to give the product shown. Tell what kind of reaction is involved and predict (with explanation) whether the reaction is thermally or photochemically allowed. (10 points)
CH 2
CH 3 OCC CCOCH 3
O O
CO 2 CH 3
CO 2 CH 3
- Draw the expected products from electrocyclic ring closure of (2 E ,4 Z ,6 Z ,8 E )- decatetraene under thermal and photochemical conditions. Explain your reasoning. (10 points)
hν
- The synthesis of the histamine H 2 -receptor antagonist cimetidine (Tagamet®) is shown below. Indicate how you would carry out the reactions indicated. ( points each)
(a) (^) (b)
(c)
HN N
S
N
C
N
CH 3
N
H H
CH 3
CN
HN N
CO 2 Et
CH 3
HN N
CH 3
OH
HN N
S
NH 2
CH 3
K 2 CO 3 HN N
S
N
C
N
H
CH 3
CN
SCH 3
N
C
CH 3 S SCH 3
CN
a) Hint: Reduction of an ester.
b) Hint: SN2 reaction.
c) Hint: Nucleophilic addition/elimination reaction.
KEY
- Draw the structure of the polymer that results from heating the following diepoxide and diamine (5 points):
O O
O O
H 2 N NH 2
+ S
N 2
O O N N
OH OH H H
n
Note that this is a nucleophilic (SN2) ring opening of an epoxide – nucleophilic attack occurs at the 1o^ carbon atom and not at the 2 o^.
- The polyurethane foam used for home insulation uses methanediphenyldiisocyanate (MDI) as the monomer. Draw the structure of a representative segment of polyurethane prepared by reaction of ethylene glycol with MDI (5 points):
O C N CH 2 N C O + HO^ OH
C
O
N
H
CH 2 N
H
C
O
O
O
n
- Epoxy adhesives are cross-linked resins prepared in two steps. The first step involves SN2 reaction of the disodium salt of bisphenol A with epichlorohydrin to form a low-molecular-weight prepolymer. This prepolymer is then “cured” into a cross-linked resin by treatment with a triamine such as H 2 NCH 2 CH 2 NHCH 2 CH 2 NH 2.
C
CH 3
CH 3
HO OH O Cl
Bisphenol A Epichlorohydrin
a) What is the structure of the prepolymer? (5 points)
n
O C CH 3
CH 3 O O C CH 3
CH 3 O
O O
OH
See: Bruice, p 1166
b) How does addition of the triamine to the prepolymer result in cross- linking? (5 points) The terminal epoxides undergo SN2 reaction with the nucleophilic amines:
n
O C CH 3
CH 3 O O C CH 3
CH 3 O
O O
OH
H 2 N N NH 2
H
H 2 N N NH 2
H
n
n
O C
CH 3
CH 3
O O C
CH 3
CH 3
O OH
O C CH 3
CH 3 O O C CH 3
CH 3 O
OH
HN NH
NH
HN
HN
NH
OH OH
OH OH
- Which of the following reactions is more likely to occur? Explain. (10 points)
H
H 2
H H
H H
a)
b)
Reaction (a) is a retro [4+2] cycloaddition and is thermally allowed. Reaction (b), on the other hand, is a retro [2+2] cycloaddition and is thermally forbidden. Therefore, reaction (a) is more likely to occur.
- Identify the pericyclic reaction involved in the following transformation. Use curved arrows to show the electron rearrangement that takes place ( points)
1
2 3
4 5
1 2
3 4 5
This is a (5,5) sigmatropic rearrangement.
- The sex hormone estrone has been synthesized by a route that involves the following step. Identify the pericyclic reactions involved, and propose a mechanism (curved arrow formalism). (10 points)
CH 3 O
O
H
O
H
H H
CH 3 O
Estrone methyl ether
electrocyclic ring-opening
O
H
CH 3 O
Diels-Alder [4+2] cycloaddition
- Vinyl-substituted cyclopropanes undergo thermal rearrangement to yield cyclopentenes. Propose a mechanism for the reaction (curved arrow formalism), and identify the pericyclic process involved. (10 points)
Vinylcyclopropane Cyclopentene
1 2
3
This is a (1,3) sigmatropic alkyl shift. Note: The reaction must proceed by an antarafacial process (inversion of configuration) at the migrating carbon atom.
- The synthesis of the histamine H 2 -receptor antagonist cimetidine (Tagamet®) is shown below. Indicate how you would carry out the reactions indicated. ( points each)
(a) (^) (b)
(c)
HN N
S
N
C
N
CH 3
N
H H
CH 3
CN
HN N
CO 2 Et
CH 3
HN N
CH 3
OH
HN N
S
NH 2
CH 3
K 2 CO 3 HN N
S
N
C
N
H
CH 3
CN
SCH 3
N
C
CH 3 S SCH 3
CN
a) Hint: Reduction of an ester.
- LiAlH 4 / THF
- H 3 O +
HS
NH 2
b) Hint: SN2 reaction.
/ H +^ cat.
CH 3 NH 2
c) Hint: Nucleophilic addition/elimination reaction.
/ K 2 CO (^3)
- The synthesis of the antidepressant drug fluoxetine (Prozac®) is shown below. Indicate how you would carry out each of the reactions. (5 points each)
Cl O Cl OH N O
H
CH 3
H
N O
H
CH 3
CF 3
(a) (b)
(c)
Fluoxetine
a) Hint: Reduction of a ketone.
- NaBH 4 / CH 3 OH
- H 3 O +
xs CH 3 NH (^2)
Note: LiAlH 4 is too powerful a reducing agent to use here – it would reduce off the Cl.
b) Hint: SN2 reaction.
/ Et 2 O
- NaH
c) Hint: Nucleophilic aromatic substitution reaction.
/ DMSO (need a strong base to deprotonate the alcohol and generate a good nucleophile)
- Cl CF (^3)
