10: Alkynes

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learning objectives

After reading this chapter and completing ALL the exercises, a student can be able to

apply bonding theories to the structure of alkynes and distinguish between internal and terminal triple bonds - refer to section 10.1
predict relative physical properties of alkynes, such as relative boiling points and solubilities - refer to section 10.1
predict the products and specify the reagents for the synthesis of alkynes from the double elimination of dihaloalkanes refer to section 10.2
predict the products and specify the reagents for the Electrophilic Addition Reactions (EARs) of alkynes with HX and X₂ - refer to section 10.3
predict the products and specify the reagents for the Markovnikov-products of alkyne hydration - refer to section 10.4
predict the products and specify the reagents for the anti-Markovnikov-products of alkyne hydration - refer to section 10.5
predict the products and specify the reagents for the full or partial reduction of alkynes - refer to section 10.6
predict the products and specify the reagents for the oxidation of alkynes - refer to section 10.7
explain why alkynes are more acidic than alkanes and alkenes - refer to section 10.8
predict the products and specify the reagents to generate nucleophilic acetylide ions and heavy metal acetylides - refer to section 10.8
predict the products and specify the reagents to synthesize larger alkynes with acetylide ions - refer to section 10.9
use retrosynthetic analysis to design a multi-step synthesis with correct regiochemistry and stereochemistry using the reactions studied to date - refer to section 10.10

Please note: IUPAC nomenclature and important common names of alkynes were explained in Chapter 3.

10.1: Structure and Physical Properties
Alkynes are unsaturated hydrocarbons with carbon-carbon triple bonds. As hydrocarbons, they are non-polar similar to alkanes. However, the two pi bonds create chemical reactivity similar to alkenes.
10.2: Synthesis 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.
10.3: Reactions of Alkynes - Addition of HX and X₂
The two pi bonds of alkynes allow them to undergo electrophilic addition reactions (EARs) similar to alkenes.
10.4: Hydration of Alkynes for Markovnikov Products
Hydration of alkynes can produce the Markovnikov products with a slight modification to the oxymercuration-demercuration reaction system for alkenes. Enol-keto tautomerism is explained and applied to the alkyne hydration mechanism.
10.5: Hydration of Alkynes for Anti-Markovnikov Products
The hydroboration-oxidation reaction we learned for alkenes is modified slightly for reactions with alkynes to produce anti-Markovniknov products. This mechanism also includes enol-keto tautomerism.
10.6: 10.6 Reduction of Alkynes
Alkynes can be fully reduced to alkanes or specialty reagents can be used to stop the reduction at the alkene. The specialty reagents are distinguished by their reaction mechanism stereochemistry to produce cis or trans alkenes.
10.7: Oxidation of Alkynes
Similar to alkenes, alkynes can be oxidized using gentle or strong reaction conditions to produce different products.
10.8: Acidity of Terminal Alkynes
Terminal alkynes are much more acidic than most other hydrocarbons. Removal of the alkyne proton is possible to form a strong nucleophile, the acetylide anion, RC=C:-, which can be used in subsequent reactions, particularly SN1 and SN2.
10.9: Synthesis of Larger Alkynes from Acetylides
The alkylation of acetylide ions is important in organic synthesis because it is a reaction in which a new carbon-carbon bond is formed building larger organic molecules.
10.10: An Introduction to Multiple Step Synthesis
Integrating the different reactions from the first 10 chapters of this text into multiple step synthetic pathways is an important skill in mastering organic chemistry.
10.11: Additional Exercises
This section has additional exercises for the key learning objectives of this chapter.
10.12: Solutions to Additional Exercises
This section has the solutions to the additional exercises from the previous section.

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