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Lecture Organic chemistry: Chapter 9 - L. G. Wade, Jr.

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Chapter 9 introduce to Alkynes. In this chapter, students will be able to: Draw and name alkynes, cycloalkynes, and their derivatives; show how to synthesize alkynes by eliminations from alkyl halides and by the additions and substitutions of acetylide ions; predict the products of the reactions of alkynes, including the orientation of the reaction (regiochemistry) and the stereochemistry;. | Chapter 9 © 2010, Prentice Hall Organic Chemistry, 7th Edition L. G. Wade, Jr. Alkynes Chapter 9 Introduction Alkynes contain a triple bond. General formula is CnH2n-2. Two elements of unsaturation for each triple bond. Some reactions resemble the reactions of alkenes, like addition and oxidation. Some reactions are specific to alkynes. Chapter 9 Nomenclature: IUPAC Find the longest chain containing the triple bond. Change -ane ending to -yne. Number the chain, starting at the end closest to the triple bond. Give branches or other substituents a number to locate their position. Chapter 9 Examples of Nomenclature All other functional groups, except ethers and halides have a higher priority than alkynes. Chapter 9 Common Names Named as substituted acetylene. methylacetylene (terminal alkyne) isobutylisopropylacetylene (internal alkyne) C H 3 C H C H 3 C H 2 C C C H C H 3 C H 3 C H 3 C C H Chapter 9 Physical Properties Nonpolar, insoluble in . | Chapter 9 © 2010, Prentice Hall Organic Chemistry, 7th Edition L. G. Wade, Jr. Alkynes Chapter 9 Introduction Alkynes contain a triple bond. General formula is CnH2n-2. Two elements of unsaturation for each triple bond. Some reactions resemble the reactions of alkenes, like addition and oxidation. Some reactions are specific to alkynes. Chapter 9 Nomenclature: IUPAC Find the longest chain containing the triple bond. Change -ane ending to -yne. Number the chain, starting at the end closest to the triple bond. Give branches or other substituents a number to locate their position. Chapter 9 Examples of Nomenclature All other functional groups, except ethers and halides have a higher priority than alkynes. Chapter 9 Common Names Named as substituted acetylene. methylacetylene (terminal alkyne) isobutylisopropylacetylene (internal alkyne) C H 3 C H C H 3 C H 2 C C C H C H 3 C H 3 C H 3 C C H Chapter 9 Physical Properties Nonpolar, insoluble in water. Soluble in most organic solvents. Boiling points are similar to alkane of same size. Less dense than water. Up to four carbons, gas at room temperature. Chapter 9 Acetylene Acetylene is used in welding torches. In pure oxygen, temperature of flame reaches 2800 C. It would violently decompose to its elements, but the cylinder on the torch contains crushed firebrick wet with acetone to moderate it. Chapter 9 Synthesis of Acetylene Heat coke with lime in an electric furnace to form calcium carbide. Then drip water on the calcium carbide: coke lime This reaction was used to produce light for miners’ lamps and for the stage. C C aO 3 + + C aC 2 C O H C C H C a( O H ) 2 C aC 2 + 2 H 2 O + Chapter 9 Molecular Structure of Acetylene Triple-bonded carbons have sp hybrid orbitals. A sigma bond is formed between the carbons by overlap of the sp orbitals. Sigma bonds to the hydrogens are formed by using the second sp orbital. Since the sp orbitals are linear, acetylene