Chem 2300
Exam 3
November 21, 2014
Name:
(Please print)
(First)
(Last)
Last 4 digits of
A Number
Score
I. Multiple Choice
(
/90
/30)
II
/10
III
/10
Total score
/110
Note: Periodic Table, pKa, and pKb values are on pages 14 and 15.
1
I. Multiple choice questions. (3 points each). Please put your answers on Scantron sheet. Your score will
be graded based only on your answers from Scantron sheet.
1. What could be the substitution product for the following reaction?
2. What could be the substitution product for the following reaction?
3. Which statements are true for SN2 reaction of alkyl halides?
I. Both of the alkyl halide and nucleophile are involved in the transition state.
II. Reaction proceeds with inversion of configuration at the substitution center.
III. Reaction proceeds via the formation of carbocation intermediate.
IV. The order of reactivity is 1°>2°>3°.
V. The nucleophile must have an unshared electron pair and bear a negative charge.
VI. Protic solvents favor SN2 reaction.
(a) II, IV, V
(b) I, II, V, VI
(c) III, V, VI
(d) I, II, IV
(e) None of the above
2
4. Which of the following alcohol would be least soluble in water?
5. What could be the product for the following reaction?
6. What could be the product for the following reaction?
3
7. What could be the product for the following reaction?
8. What is the possible mechanism for the reaction in Q.7?
(a) SN1
(b) SN2
(c) E1
(d) E2
(e) None of the above
9. What could be the major product for the following reaction?
10. What is the name for the following compound?
(a) (E)-N-ethyl-3-pentenamide
(b) (Z)-N-ethyl-3-pentenamide
(c) (E)-N-ethyl-4-pentenamide
(d) (Z)-N-ethyl-4-pentenamide
(e) None of the above
4
11. What is the name for the following compound?
(a) (R)-3-methylhexanoic acid
(b) (S)-3-methylhexanoic acid
(c) (R)-3-methylhexyl acid
(d) (S)-3-methylhexyl acid
(e) None of the above
12. What is the name for the following compound?
(a) cyclopentylcarbonyl chloride
(b) cyclopentanecarbonyl chloride
(c) cyclopentylacyl chloride
(d) cyclopentaneacyl chloride
(e) None of the above
13. What is the name for the following compound?
(a) benzoyl chloride
(b) benzyl chloride
(c) benzene chloride
(d) phenyl chloride
(e) None of the above
14. The active ingredient in Tylenol is acetaminophen. Which of the following reagent cannot be used
for the preparation of acetaminophen from 4-hydroxyaniline?
(a) CH3COCl, N(CH2CH3)3
(b) (CH3CO)2O, N(CH2CH3)3
(c) CH3CO2CH3, heating
(d) CH3CONH2, N(CH2CH3)3
(e) None of the above
5
N,N-Diethyl-meta-toluamide, abbreviated DEET, is a slightly yellow oil. DEET is the most common
active ingredient in insect repellents developed by the United States Army, following the experience of
jungle warfare during World War II. DEET can be prepared using m-toluic acid (3-methylbenzoic acid)
as the starting material. Answer questions 15 - 16 based on the following scheme for the synthesis of
DEET.
15. What should be the structure of I?
16. What could be reagent A?
(a)
(b)
(c)
(d)
(e)
Methylamine
Dimethylamine
Ethylamine
Diethylamine
None of the above
17. n-Octyl acetate is a commonly used artificial flavor to mimic orange flavor. What are the compounds
required for the preparation of n-octyl acetate?
(a)
OH
OH
and
O
(b)
OH
and
OH
O
(c)
OH
and
OH
O
(d)
OH
OH
and
O
(e) None of the above
6
18. One of the esters found in beeswax has the chemical formula of C15H31CO2C30H61. Which of the
following synthetic scheme can be used to prepare this specific beeswax?
19. What could be the product for the following reaction?
O
NH
(a)
O
HCl, H2O, heat
Product?
(c)
(b)
OH
O
H3 N
(d)
NH2
OH
HO
H2N
Cl-
O
O
(e) None of the above
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O
2,4-Dichlorophenoxyacetic acid (2,4-D) is a common systemic pesticide/herbicide for controlling the
growth of broadleaf weeds, such as dandelion. It can be synthesized from 2,4-dichlorophenol and
chloroacetic acid. Answer questions 21-22.
20. What is the most likely reaction/mechanism for the synthesis of 2,4-D?
(a)
(b)
(c)
(d)
(e)
SN1
SN2
Electrophilic aromatic substitution
Nucleophilic acyl substitution
None of the above
21. What is the role of K2CO3 in the synthesis of 2,4-dichlorophenol?
(a)
(b)
(c)
(d)
(e)
electrophile
nucleophile
base
solvent
None of the above
Based on the following reaction scheme, answer question 22 – 24.
CN
Br
H
H3C
H
H3C
+
CN-
H
+ H3C
CN
I
+
Br-
II
22. If this reaction goes through SN1 mechanism exclusively, what will be the ratio of compound I vs.
compound II?
(a)
(b)
(c)
(d)
(e)
I/II = 50/50
I/II = 100/0
I/II = 0/100
I/II = 30/70
None of the above
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23. If this reaction goes through SN2 mechanism exclusively, what will be the ratio of compound I vs.
compound II?
(a)
(b)
(c)
(d)
(e)
I/II = 50/50
I/II = 100/0
I/II = 0/100
I/II = 30/70
None of the above
24. If 40% of the reaction goes through SN1 mechanism and 60% of the reaction goes through SN2
mechanism, what will be the ratio of compound I vs. compound II?
(a)
(b)
(c)
(d)
(e)
I/II = 80/20
I/II = 60/40
I/II = 40/60
I/II = 20/80
None of the above
Answer Q. 25-27 based on the following scheme:
25. What is compound I?
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26. What is compound II?
27. What is compound III?
28. What could be the product for the following reaction?
10
29. What could be the product for the following reaction?
30. What could be the product for the following reaction?
Continue to the Next Page
11
II. Bio-diesel can be prepared by reacting fats or oils, for example, tripalmitoylglycerol with alcohols
(methanol) under the catalysis of acids, a reaction known as transesterification. Propose an electronpushing mechanism for the formation of the bio-diesel shown in the following scheme. Note: you only
need to show the conversion of one ester group. (10 points)
O
C
H2C
O
O
(CH2)14CH3
O
H2C
O
O
OH
HC
OH
H2C
OH
H+
C
HC
H2C
(CH2)14CH3
+ 3 CH3OH
C
C
(CH2)14CH3
glycerol
tripalmitoylglycerol
12
O
+ 3 CH3O
(CH2)14CH3
a bio-diesel
III. (Bonus) Soaps can be prepared by hydrolysis of fats or oils, for example, tripalmitoylglycerol with
base (NaOH), a reaction known as saponification. Propose an electron-pushing mechanism for the
formation of the soap shown in the following scheme. Note: you only need to show the conversion of
one ester group. (10 points)
Next Pages: Periodic Table, pKa, and pKb Values
13
pKa Values for Selected Organic and Inorganic Acids
Acid
Formula
pKa
Conjugate Base
Ethane
CH3CH3
51
CH3CH2Ammonia
NH3
38
NH2Ethanol
CH3CH2OH
15.9
CH3CH2OWater
H2O
15.7
HO+
Methylammonium ion
CH3NH3
10.64
CH3NH2
Bicarbonate ion
HCO310.33
CO32Phenol
C6H5OH
9.95
C6H5OAmmonium ion
NH4+
9.24
NH3
Carbonic acid
H2CO3
6.36
HCO3Acetic acid
CH3CO2H
4.76
CH3CO2Benzoic acid
C6H5CO2H
4.19
C6H5CO2Phosphoric acid
H3PO4
2.1
H2PO4Hydronium ion
H3O+
-1.74
H2O
Sulfuric acid
H2SO4
-5.2
HSO4Hydrogen chloride
HCl
-7
ClHydrogen bromide
HBr
-8
BrHydrogen iodide
HI
-9
I-
14
pKb Values for Selected Amines and pKa Values for Their Conjugate Acids
Amine
Formula/Structure
pKb
Conjugate Acid
methylamine
CH3NH2
3.36
CH3NH3+
ethylamine
CH3CH2NH2
3.19
CH3CH2NH3+
dimethylamine
(CH3)2NH
3.27
(CH3)2NH2+
diethylamine
(CH3CH2)2NH
3.02
(CH3CH2)2NH2+
trimethylamine
(CH3)3N
4.19
(CH3)3NH+
triethylamine
(CH3CH2)3N
3.25
(CH3CH2)3NH+
NH2
pKa
10.64
10.81
10.73
10.98
9.81
10.75
NH3
aniline
9.37
4.63
NH2
4-methylaniline
NH3
8.92
H3C
5.08
H3C
NH2
4-chloroaniline
NH3
9.85
Cl
4.15
Cl
NH2
4-nitroaniline
NH3
13.0
O 2N
1.0
O 2N
H
N
pyridine
N
8.75
H
N
H
N
imidazole
5.25
7.05
6.95
N
N
H
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