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Chem 221 Fall 1997 Exam III
1) a) List the following alkoxide nucleophiles in order of decreasing SN2 reactivity: Me3CO-, MeO-,
MeCH2O-, Me2CHO-.
b) After answering the question above, criticize the generalization that for a given nucleophilic atom
nucleophilicity parallels basicity.
2) Draw the reaction energy diagrams (on the same graph showing relative energetic positions) for the
SN1 and SN2 mechanistic possibilities for the reaction shown. Provide structures for all transition states
and intermediates in your diagram.
CH3-Br + Na+ -OH ------> CH3-OH + Na+ Br -
3) Draw an alkyl halide (showing stereochemistry via a sawhorse projection) which will yield (E)-2phenyl-2-butene when treated with Na+ -OEt. Provide a mechanism for this reaction.
4) Provide two possible routes for preparing the ether shown below. Which method do you think would
work best and why in 1 sentence? Provide a mechanism for the method which you think is best.
O
5) Draw the 3 possible diastereomers of 2-chloro-1,3-dimethylcyclohexane and indicate which cannot
undergo E2 elimination when treated with strong base. For those that can undergo E2 provide the
expected major product and a mechanism for its formation.
6) Provide alkyl halides, nucleophiles/bases, or major products as requested for the reactions below.
Indicate whether the major reaction pathway will be SN1, SN2, E1 or E2. If stereochemistry is important,
indicate it in your drawing.
OH
H 2SO 4

K + - OtBu
tBuOH
Br
H 2O
Na + - SCH 2CH 3
CH 3CH 2CH 2CH 2I
Br
acetone
?
OCH 2CH 3
acetone
Na + - OEt
EtOH
CH 3Br + Na +
-
C
N
acetone
Na + Br - , H 2SO 4
CH 3CH 2CH 2CH 2OH
7) Provide a structure consistent with the spectroscopic data provided. Assign all peaks in the proton
NMR to protons in your proposed structure.
7) Draw meso-2,3-dibromobutane. If 1 mole of this compound was treated with 1 mole of a strong base
like sodium ethoxide, what would the major product be (show stereochemistry)? Provide a mechanism
to account for the formation of this major product and name it.
5) Could the following reactions be used to prepare the organic products indicated as the major product?
If you answer yes, what substitution or elimination reaction pathway would account for the formation of
the major product? If you answer no, what would be the major product?
6) The following are the relative rates observed for the formation of alcohols from the listed alkyl
halides in 80% water and 20% ethanol at 25oC. How would you explain this information and account
for the minimum value for (CH3)2CHBr?
CH3Br CH3CH2Br
2140
171
(CH3)2CHBr
4.99
(CH3)3CBr
1010
7) Account for the stereochemical results shown in the reactions below. Provide a mechanism for the
formation of racemic (1) and both racemic and inverted (2). Why do you think this particular secondary
halide participates in substitution reactions that lead to alot of racemization?
I give my word that I will communicate with no one in any manner through any medium about the
content of this exam until after 12:00noon Wednesday, November 30, 1994.
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