Further chemistry of alkenes and alkynes is described in this chapter, with emphasis on addition reactions that lead to reduction and oxidation of carbon- carbon multiple bonds. First we explain what is meant by the terms reduction and oxidation as applied to carbon compounds. Then we emphasize hydrogenation, which is reduction through addition of hydrogen, and oxidative addition reactions with reagents such as ozone, peroxides, permanganate, and osmium tetroxide. We conclude with a section on the special nature of 1-alkynes, their acidic behavior, and how the conjugate bases of alkynes can be used in synthesis to form carbon-carbon bonds.
- 11.1: Oxidation-Reduction of Organic Compounds
- An organic compound commonly is said to be "reduced" if reaction leads to an increase in its hydrogen content or a decrease in its oxygen content. The compound would be "oxidized" if the reverse change took place.
- 11.2: Hydrogenation with Heterogeneous Catalysts
- Addition of hydrogen to a multiple bond is hydrogenation. It is applicable to almost all types of multiple bonds and is of great importance in synthetic chemistry, particularly in the chemical industry.
- 11.3: Heats of Hydrogenation
- Catalytic hydrogenation is useful for analytical and thermochemical purposes. The analysis of a substance for the number of carbon-carbon double bonds it contains is carried out by measuring the uptake of hydrogen for a known amount of sample. Measurement of the heat evolved in the hydrogenation of alkenes gives information as to the relative stabilities of alkenes.
- 11.4: Hydrogenation with Homogeneous Catalysts
- Hydrogen addition to multiple bonds is catalyzed by certain complex metal salts in solution. This may be described as homogeneous catalysis and, compared to heterogeneous catalysis, is a relatively new development in the area of hydrogenation reactions. Rhodium and ruthenium salts appear to be generally useful catalyst.
- 11.5: Hydrogenation with Diimide
- There are alternative ways to add hydrogen to a multiple bond besides the catalytic methods described in the previous sections. For example, hydrogen can be added to a multiple bond via homogeneous reactions utilizing diimide and diborane.
- 11.6: Addition of Boron Hydrides to Alkenes. Organoboranes
- Hydroboration and the many uses of organoboranes in synthesis were developed largely by H. C. Brown and co-workers. In our discussion, we shall give more detail on hydroboration itself, and then describe several useful transformations of organoboranes.
- 11.7: Oxidation Reactions
- Most alkenes react readily with ozone, even at low temperatures, to yield cyclic peroxidic derivatives known as ozonides. Ozonization of alkenes has been studied extensively for many years, but there is still disagreement about the mechanism (or mechanisms) involved because some alkenes react with ozone to give oxidation products other than ozonides. Several oxidizing reagents react with alkenes under mild conditions to give, as the overall result, addition of hydrogen peroxide.
- 11.8: Terminal Alkynes as Acids
- A characteristic and synthetically important reaction of ethyne and terminal alkynes is salt (“acetylide”) formation with very strong bases. In such reactions the alkynes behaves as an acids in the sense that they give up protons to suitably strong bases.
- 11.E: Alkenes and Alkynes II (Exercises)
- These are the homework exercises to accompany Chapter 11 of the Textmap for Basic Principles of Organic Chemistry (Roberts and Caserio).
Contributors and Attributions
John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."