9: Alkynes - An Introduction to Organic Synthesis — Read

From LibreTexts, under CC BY-NC-SA 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

Learning Objectives

After you have completed Chapter 9, you should be able to

fulfillall of the detailed objectives listed under each individual section.
solve road-map problems involving any of the reactions introduced to this point.
design multistep syntheses using any of the reactions introduced to this point, and determine the viability of a given synthesis.
define, and use in context, the key terms introduced.

Addition reactions not only dominate the chemistry of alkenes, they are also the major class of reaction you will encounter. This chapter discusses an important difference between (terminal) alkynes and alkenes, that is, the acidity of the former; it also addresses the problem of devising organic syntheses. Once you have completed this chapter you will have increased the number of organic reactions in your repertoire, and should be able to design much more elaborate multistep syntheses. As you work through Chapter 9, you should notice the many similarities among the reactions described here and those in Chapters 7 and 8.

9.0: Why This Chapter?
9.1: Preparation of Alkynes - Elimination Reactions of Dihalides
Alkynes can be a useful functional group to synthesize due to some of their antibacterial, antiparasitic, and antifungal properties. One simple method for alkyne synthesis is by double elimination from a dihaloalkane.
9.2: Reactions of Alkynes - Addition of HX and X₂
9.3: Hydration of Alkynes
As with alkenes, hydration (addition of water) to alkynes requires a strong acid, usually sulfuric acid, and is facilitated by mercuric sulfate. However, unlike the additions to double bonds which give alcohol products, addition of water to alkynes gives ketone products ( except for acetylene which yields acetaldehyde ). The explanation for this deviation lies in enol-keto tautomerization.
9.4: Reduction and Oxidation of Alkynes
Reactions between alkynes and catalysts are a common source of alkene formation. Because alkynes differ from alkenes on account of their two procurable π bonds, alkynes are more susceptible to additions. Aside from turning them into alkenes, these catalysts affect the arrangement of substituents on the newly formed alkene molecule. Depending on which catalyst is used, the catalysts cause anti- or syn-addition of hydrogens. Alkynes can readily undergo additions because of their availability of tw
9.5: Alkyne Acidity - Formation of Acetylide Anions
Terminal alkynes are much more acidic than most other hydrocarbons. Removal of the proton leads to the formation of an acetylide anion, RC=C:-. The origin of the enhanced acidity can be attributed to the stability of the acetylide anion, which has the unpaired electrons in an sp hybridized orbital. The stability results from occupying an orbital with a high degree of s-orbital character.
9.6: Alkylation of Acetylide Anions
The alkylation of acetylide ions is important in organic synthesis because it is a reaction in which a new carbon-carbon bond is formed; hence, it can be used when an organic chemist is trying to build a complicated molecule from much simpler starting materials.
9.7: An Introduction to Organic Synthesis
9.8: Chemistry Matters—The Art of Organic Synthesis
9.A: Alkynes - An Introduction to Organic Synthesis (Summary)
9.B: Additional Problems

This page titled 9: Alkynes - An Introduction to Organic Synthesis was last modified on Wed, 10 Jul 2024 16:42:58 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Sol Parajon Puenzo (Cañada College) via source content that was edited to the style and standards of the LibreTexts platform.

Contents

Text

Learning Objectives