Organic Chemistry
novocaine

Professor Carl C. Wamser

Chem 334 - Fall 2003

Workshop 6

Chapter 6 Workshop Problems
Alkene Reactions and Eliminations

1. All of the following reactions occur by analogous mechanisms. Write a single, general mechanism that explains all of these reactions. Make a table listing the electrophiles and the nucleophiles, reaction by reaction, for the first mechanistic step and also for the second mechanistic step.

RCH=CH2 + Cl2 ---> RCHClCH2Cl

RCH=CH2 + Cl2 (in H2O) ---> RCH(OH)CH2Cl

RCH=CH2 + Br2 ---> RCHBrCH2Br

RCH=CH2 + Br2 (in CH3OH) ---> RCH(OCH3)CH2Br

RCH=CH2 + HCl ---> RCHClCH3

RCH=CH2 + HBr ---> RCHBrCH3

RCH=CH2 + HI ---> RCHICH3

RCH=CH2 + H2SO4 --->

RCH=CH2 + H2SO4 (in H2O) ---> RCH(OH)CH3

RCH=CH2 + H2SO4 (in CH3OH) ---> RCH(OCH3)CH3

RCH=CH2 + Hg(O2CCH3)2 (in H2O) ---> RCH(OH)CH2-HgO2CCH3

RCH=CH2 + Hg(O2CCF3)2 (in CH3OH) ---> RCH(OCH3)CH2-HgO2CCF3

2. a. The reaction of 3-methyl-2-butanol with HBr gives 2-bromo-2-methylbutane. Write a complete mechanism that explains why this is the major reaction product. The "expected" product, 2-bromo-3-methylbutane, can be formed by adjusting the reaction conditions to include a large excess of NaBr. Show how you would modify the mechanism to include a pathway to this product.

b. The reaction of 3-methyl-2-butanol with hot H3PO4 gives three elimination products, in yields of 64%, 33% and 3%. Write a complete mechanism, which should start out analogously to part (a) above, and predict the structures of the three products. Why are substitution products formed in part (a) but are not formed in this case?

3. Elimination from 1-chloro-2-isopropylcyclohexane can give different products, as shown below. Write good chair forms for the two conformations of the cis isomer and write a detailed electron-pushing mechanism to predict the preferred product in this case.

Do the same with the trans isomer. Explain the distinctive differences in the two cases.

One of the isomers reacts much faster than the other. Predict which is faster and explain the difference.

Materials adapted from:

Peer-Led Team Learning: Organic Chemistry, 1/e
Jack A. Kampmeier, University of Rochester
Pratibha Varma-Nelson, St. Xavier University
Donald Wedegaertner, University of the Pacific
Prentice-Hall, 2001, ISBN 0-13-028413-0

http://www.sci.ccny.cuny.edu/~chemwksp/OrganicChem.html