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CH 391
Fall 2003
Professor Bauld
1st Quiz
__________________________________
Name (Last, First)
I.
II.
III.
IV. __________
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I. Acid-Catalyzed Hydration of Alkenes.
1. [7 pts] Write the detailed mechanism for the acid-catalyzed hydration of
isobutene (methylpropene).
H3C
H
H3C
H
(H3O )
+ H2O
2. [7 pts] Using resonance theory, develop a TS model for the rate-determining
step of this reaction, summarize it as a single DL/PC structure, and carefully
characterize this TS.
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3. [7 pts] Draw a reaction path diagram for this reaction and use it to illustrate
and explain the two requirements for a step to be rds.
4. [3 pts] State the Hammond Principle in its most succinct form and apply it to
the rds of this reaction to refine your characterization.
5. [6 pts] Use the method of competing TS’s to rationalize the regiochemistry of
this reaction. Recall that this requires you to write down (not derive) the TS
for both of the regiochemical modes and to characterize each one.
6. [6 pts] Use the method of competing transition states (2 TS’s and characters)
to predict the relative rates of hydration of propene and isobutene.
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II. Hoffmann Eliminations
1. [7 pts] Using resonance theory, develop a TS model for the generalized E2
elimination reaction shown below, summarize as a DL/PC structure, and fully
characterize the TS model.
H
C
C
+ OH
NMe3
2. [6 pts] Use the method of competing TS’s (2 TS’s) to develop a prediction of
the results of the following elimination and explain in terms of your TS
models.
H3C
NMe3
+ OH
3. [4 pts] Explain why the dominant character of the TS for Hoffmann
eliminations is different from that in Zaitsev eliminations of alkyl chlorides.
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III. Miscellaneous Mechanistic Questions
A. 1. [7 pts] Provide a resonance theoretical treatment of the epibromonium ion
intermediate involved in the addition of bromine to propene, summarize as a single dotted
line/partial charge structure, and characterize this intermediate.
Br
H3C
H
H
H
2. [5 pts] Indicate at which carbon the carbocation character is greater and explain
why, using resonance theory.
3. [5 pts] Apply the Hammond principle to the transition state for the reaction of this
epibromonium ion with methanol. What kind of bonding is primarily involved in the
reaction with the methanol nucleophile? Indicate where the nucleophile reacts and
explain why.
B. 1. [3 pts] Indicate what provides the thermodynamic driving for the elimination
reaction shown below.
H
C
+ OH
C
C
C
+ H2O
Cl
2. [5 pts] Provide an estimate of the amount of this driving force in kcal/mol. It is not
important for this exam question that you get the answer exactly right, but that you use a
valid approach to obtaining the approximate result.
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IV. Hydroboration
1. [7 pts] Use resonance theory to develop a TS model for the hydroboration of
propene, summarize as a DL/PC, and carefully characterize the TS.
H3C
H
H
H
+ R2BH
2. [6 pts] Use this TS model and character and the method of competing TS’s
(two TS’s and characters) to rationalize the regiochemical result in the
hydroboration of propene.
3. [3 pts] Mention and explain one other factor which also tends to favor the
same regiochemical mode.
4. [3 pts] What is the appropriate phraseology which is used to describe the
reaction stereochemistry?
4. [3 pts] Predict the regio- and stereochemistry of the hydroboration/oxidation
product of the following substrate.
CH3
1. R2BH
2. H2O2, OH