Chem220 - Organic Chemistry

Problem Set 4

Chapter 5: Alkenes: Addition Reactions

Due: Monday, October 10, 2011


In 1840, Christian Friedrich Schönbein (1799-1868) discovered ozone (Gr.; odorant), the sharp odor produced by electrical discharges. Seven years later (1847) he observed that ozone oxidizes organic compounds but not to their ultimate products of oxidation, carbon dioxide and water. [Two years prior, he had spilled nitric and sulfuric acid on his Frau's apron in her kitchen. The apron, made of cotton, combusted and thus was discovered gun cotton, nitrocellulose. Schönbein also observed that hydrogen peroxide (Threnard; 1818) is oxidized to oxygen gas in the presence of hemoglobin. ] In the period 1903-1916, Carl Dietrich Harries (1866-1923), an assistant to both Hofmann (of the eponymous elimination and rearrangement) and Fischer (of projection and carbohydrate fame) at Berlin, published some 80 papers on the reactions of ozone with organic compounds. His interest was stimulated by the reaction of ozone with rubber, a process that causes rubber to become hard and brittle. These studies led to the analytical and synthetic uses of ozone. From 1904-1916 he was a professor at Kiel. Disenchanted with academic life, he became Director of Research for Siemens and Halske, the German company co-founded by the electrical pioneer, Werner von Siemens, his father-in-law. Not surprisingly, Siemens went into the business of producing ozone generators. The studies of Rudolf Criegee (1902-1975; Karlsruhe) produced a unified mechanism for the process of ozonolysis.

M. Rubin, Bull. Hist. Chem., 2001, 26, 40.

M. Rubin, Helv. Chem. Acta, 2003, 86, 930.

Reading Assignments:

a)The alkane and alkene modules in ORGO will help with this Problem Set.. [Note that some of the problems in the alkene module deal with stereochemical issues. We will get there.]

b) Ozonolysis module.

 

Rudolf Criegee

(1904 - 1975)

1) Predict the major product in each of the following reactions. Use the curved arrow formalism to illustrate how each intermediate is formed.

 

2) Study problem #1 in the Alkane Module in ORGO. Using bond dissociation energies, calculate the heat of each propagation step and the heat of the overall reaction. Now determine the heat of formation of 2-chloro-2-methylbutane using the heats of formation table.

3) There are four possible constitutional isomers arising from the free radical monochlorination of 2-methylbutane. The relative reactivity of C-H bonds sp3 hybridized alkanes toward chlorine atoms is: primary, 1; secondary, 4.5; tertiary, 5.5. What are the structures of these monochloro compounds (C5H11Cl)? How much of each one is formed? Show work.

4) Hydroboration and oxidation of either (E)- or (Z)-3-hexene forms 3-hexanol efficiently. Why? Can the 2-hexenes be substituted for 3-hexene? Explain.

5) Provide reaction conditions for each of the following reactions. Provide commentary.