Organic Chemistry CHM 252 and CHM 254L
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CHM 252 Organic Chemistry II
Spring 2001
Workshop #6

1.  Discuss your answers to the four model systems that I introduced on the blackboard in lab on Thursday (nitration of toluene, chlorobenzene, anisole, and nitrobenzene).  Focus on step III in order to determine whether the ortho/para products or the meta product is/are formed.

2.  Celestolide, a perfuming agent with a musk odor, is prepared by the following sequence of reactions.

  1. Give the curved-arrow mechanism for both reactions.
  2. Draw the structure of celestolide and rationalize its structure by critical examination of your proposed reaction mechanism.

3.  Draw reaction free energy profiles in which substitution on benzene by a general electrophile (E+) is compared with substitution at BOTH the meta and para positions of aniline.

  1. Before you begin writing out the mechanism for the reactions, discuss the FOUR STEPS involved in EAS.
  2. Be sure to describe whether the ring system is activated or deactivated (relative to benzene). Provide support by evaluating the inductive and resonance effects of the ring substituent.
  3. For the anisole reactions, indicate which will be fastest and which will be slowest and determine where you expect E+ to be directed (meta or para) --- this will require you to write out the full mechanism for meta and para (like we did in lab with the 4 model systems) and evaluate ALL potential resonance structures (Step III) in order to determine which series is most "effective".

4.  Repeat question #3 using benzaldehyde as your starting material instead of aniline.  Be sure to compare with the standard, benzene.

5.  Complete the following reactions by drawing the structure(s) of the product(s) and be prepared to explain your answer (you might have a mixture of major and minor products). You’ll probably want to work through the mechanisms for each reaction in order to predict the relative stability of the resonance stabilized C+ intermediates. A weighing of the relative importance of resonance structures will enable you to predict the directing effect of ring substituents.

 

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Timm A. Knoerzer
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Naz Chem. Dept.
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Last Updated Thursday, March 01, 2001 07:33:15 PM