Chem 2301 (Organic Chemistry I)
Hour Exam 2
April 21, 2009
1. Consider the following two-step synthetic scheme designed for preparation of t-butyl methyl
ether from isobutane. (60 pts)
Step 1 Step 2
CH3 Br2 CH3 CH3OH CH3
H3 C H H3C Br H3 C OCH3
CH3 heat CH3 heat CH3
(a) What would be a role of “heat” in the step 1? How does it work?
(b) Write a reasonable mechanism for the formation of t-butyl bromide in the step 1. You should be able
to explain all the events (reactions) from the start to the end of the reaction.
(c) Draw the structures of all the possible monobromination products in the step 1 and indicate which
one would be the major product and why that would be so.
(d) Write a reasonable mechanism for the formation of t-butyl methyl ether in the step 2.
(e) Another possible product in the step 2 is isobutylene (2-methylpropene). And it was found that the
reaction rates for the formation of alkene products are similar from (CH3)3CBr or (CD3)3CBr. Explain.
(f) It is tempting to substitute the bromination (step 1) by cheaper chlorination in the step 1 during this
economic crisis. Explain in detail what the consequences of the change would be?
2. Explain. (50 pts)
Rank the following alkene isomers (C5H10) in the
decreasing order of the heat of combustion and explain
why the order should be like that: 1-pentene, 2-methyl-2-
butene, cis-2-pentene, trans-2-pentene
Explain the following 2 facts,
Neomenthyl chloride 1. The products in the two reactions
c are different.
NaOC2H5 2. The reaction of neomenthyl
chloride is 200 times as fast as
Cl menthyl chloride.
OH H2SO4 (cat)
3% 33% 64%
OH H3PO4 O One should be able 1) to clarify the
+ Reaction 1 dramatic difference in products
depending on the use of different
e acid catalysts and 2) to provide a
OH HBr Br method of reaction by which the
Reaction 2 formation of dicyclohexyl ether is
minimized in the reaction 1.