In the Classroom
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Electrophilic Additions to Alkenes Thomas M. Bertolini* and Phuc D. Tran Department of Chemistry, University of California, Irvine, CA 92697-2025; *
[email protected] This worksheet was designed for second-year undergraduate students who are learning alkene electrophilic addition reactions. We have used it as both a homework assignment and as a nongraded problem set for several quarters with excellent feedback from students. The puzzle format alleviates the anxiety that many students feel toward learning organic chemistry and motivates them to work the problems (1). When we spoke to students, who overwhelmingly enjoyed the worksheet, several mentioned the reward of solving the riddle was an incentive for them to work through the problems. A puzzle is fun to solve but a problem set does not have this sort of appeal to students. We in-
clude a paragraph with the worksheet both as a brief introduction to alkene chemistry and as instructions to solve the puzzle. The answer is also included. W
Supplemental Material
The worksheet, on one page, is available in this issue of JCE Online. Literature Cited 1. Bertolini, Thomas. J. Chem. Educ. 2002, 79, 828.
Worksheet Compared to alkanes, which only react with halogens and molecular oxygen, alkenes (or olefins) are much more reactive. The following 18 reactions illustrate the variety of electrophilic addition reactions to alkenes. To solve the puzzle below, complete the reactions (paying attention to stereochemistry) and match each reaction number with the letter of its product. Some of the products are used more than once. In the 18 spaces at the end of the worksheet, write the letter of the product in the blank corresponding to the reaction number.
Reactions: 3
CH3
O 1. RCOH
7
H 2 SO4 H2O
11
4
H2, Ni
CH3 1. OsO4 2. NaHSO3, H 2O
CH3OH
CH3
10
1. O3
CH3
1. Hg(OAc)2, H 2O
15
CH3 Br2
2. NaBH4
CH3
17
1. BH3
H2O
CH3
1
HBr
2. H2O2, NaOH, H2O
8
Br2 CH2Cl2
5
H2SO4
2. CH 3 SCH3 ,
6
CH3
2. CH3MgBr, + then H3O
3 atm
18
2
CH3 HBr
peroxides, ∆
13
H2SO4
16
HBr
CH3
H3O+
H2O
14
CH3
9
H2, Ni 3 atm
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Journal of Chemical Education
CH3
12
CH3
Br2
CH3OH
CH3OH
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H2SO4
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In the Classroom
Answers of the Reactions: Br
A
Br
OH CH3
B
OH
C
OCH3 CH3
HO
D
CH3
CH3 OH
E
CH3 OCH3
F
HO(CH2)4CHCH3 + enantiomer
+ enantiomer
Br
OH CH3
G
HO
CH2OH
H
I
Br
OH CH3
L
+ enantiomer
+ enantiomer
O
+ enantiomer
CH3 Br
CH3
R
S
O
Br
M
CH3
+ enantiomer
T
O
Br
Br
Br
N
CH3
+ enantiomer
CH3
V
Br
OCH3 CH3
HO
CH3
+ enantiomer
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HO
OH CH3
HC(CH2)4CCH3 4 stereoisomers
+ enantiomer
+ enantiomer
Fill in the blanks to answer the riddle. Question:
How was the alkene able to learn all of its electrophilic reactions?
Answer:
Because an
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
!
Answer: Because an olefin never forgets!
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Journal of Chemical Education
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