Chem 2301 (Organic Chemistry I) Hour Exam 2

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					                                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)
     a                                                                                  mechanism

         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,
                       Cl                                                               individually.
            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.
           Menthyl chloride

             OH      H2SO4 (cat)
                                               +             +
     d                   heat
                                         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.