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 2800C. • 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)