《有机化学》课程PPT教学课件（Official PPT of Organic Chemistry, 7th Edition, L. G. Wade, Jr.Pearson Education）Chapter 09 Alkynes

Organic Chemistry,7th Editior L.G.Wade,Jr. H Chapter 9 Alkynes Copyright 2010 Pearson Education,Inc

Chapter 9 Copyright © 2010 Pearson Education, Inc. Organic Chemistry, 7th Edition L. G. Wade, Jr. Alkynes

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 2

Chapter 9 2 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

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 3

Chapter 9 3 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

Examples of Nomenclature H,C=C一C=C-CH3CH,一CH一C=C-H CH一C=C-CH一CH,CH CH OH OCH, IUPAC name: 2-methyl-I-penten-3-yne 3-butyn-2-ol 4-methoxy-2-hexyne new IUPAC name: 2-methylpent-1-en-3-yne but-3-yn-2-ol 4-methoxyhex-2-yne Copyright 2010 Pearson Prentice Hall,Inc. All other functional groups,except ethers and halides have a higher priority than alkynes. Chapter 9 4

Chapter 9 4 Examples of Nomenclature • All other functional groups, except ethers and halides have a higher priority than alkynes

Common Names Named as substituted acetylene. CH3-C=CH methylacetylene (terminal alkyne) CH3 CH3 CH3-CH-CH2-C=C-CH-CH3 isobutylisopropylacetylene (internal alkyne) Chapter 9 5

Chapter 9 5 Common Names Named as substituted acetylene. methylacetylene (terminal alkyne) isobutylisopropylacetylene (internal alkyne) CH3 CH CH3 CH2 C C CH CH3 CH3 CH3 C CH

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 6

Chapter 9 6 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

Acetylene Acetylene is used in welding torches. In pure oxygen,temperature of flame reaches2800°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 7

Chapter 9 7 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

Synthesis of Acetylene Heat coke with lime in an electric furnace to form calcium carbide. Then drip water on the calcium carbide: 3 C CaO CaC2 CO coke lime CaC2 2 H2O H-C≡C-H+Ca(OH)2 This reaction was used to produce light for miners'lamps and for the stage. Chapter 9 8

Chapter 9 8 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. 3 C + CaO CaC2 + CO CaC2 + 2 H2O H C C H + Ca(OH)2

Molecular Structure of Acetylene H Copyright2010 Pearson Prentice Hall,Inc. 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 will be a linear molecule. Chapter9 9

Chapter 9 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 will be a linear molecule

Overlap of the p Orbitals of Acetylene H Ho bond o bond G bond H overlap of p orbitals cylinder of clectron density EPM of acetylene Copyright 2010 Pearson Prentice Hall,Inc. Each carbon in acetylene has two unhybridized p orbitals with one nonbonded electron.It is the overlap of the parallel p orbitals that form the triple bond (2 pi orbitals). Chapter 9 10

Chapter 9 10 Overlap of the p Orbitals of Acetylene Each carbon in acetylene has two unhybridized p orbitals with one nonbonded electron. It is the overlap of the parallel p orbitals that form the triple bond (2 pi orbitals)