Chapter 3 provides knowledge of radical halogenation. The main contents of this chapter include all of the following: Radical halogenation and bond strength, bond dissociation energy tables, C-H bond strengths, structure of alkyl radicals, hyperconjugation, more neighboring bonds: more hyperconjugation, radical halogenation: methane and chlorine,. | Chapter 3: Radical Halogenation O O O O N 7/29/2015 © Univesity of California 1 The first free flight of NASA’s X-43A hypersonic research aircraft. Most supersonic aircraft produce exhaust gases containing molecules such as nitric oxide (NO), whose radical reactions are destructive to the Earth’s stratospheric ozone layer. In the 1970s the United States abandoned plans to build a fleet of supersonic aircraft (SSTs, or supersonic transports) for just this reason. In contrast, the X-43A is hydrogen fueled, posing no risk to stratospheric ozone, and may represent the first step toward the development of environmentally acceptable high-speed flight Radical Halogenation And Bond Strength Reactions require bond breaking and bond making Bond strengths: homolytic cleavage radicals ∆H = DHº = Bond dissociation energy (kcal mol-1) This process contrasts with heterolytic cleavage A B A B + - + A B A· B + For example: H2O + H2O H3O + OH + - · ∆H facile but H OH, DHº = +119 Example: Calculate . | Chapter 3: Radical Halogenation O O O O N 7/29/2015 © Univesity of California 1 The first free flight of NASA’s X-43A hypersonic research aircraft. Most supersonic aircraft produce exhaust gases containing molecules such as nitric oxide (NO), whose radical reactions are destructive to the Earth’s stratospheric ozone layer. In the 1970s the United States abandoned plans to build a fleet of supersonic aircraft (SSTs, or supersonic transports) for just this reason. In contrast, the X-43A is hydrogen fueled, posing no risk to stratospheric ozone, and may represent the first step toward the development of environmentally acceptable high-speed flight Radical Halogenation And Bond Strength Reactions require bond breaking and bond making Bond strengths: homolytic cleavage radicals ∆H = DHº = Bond dissociation energy (kcal mol-1) This process contrasts with heterolytic cleavage A B A B + - + A B A· B + For example: H2O + H2O H3O + OH + - · ∆H facile but H OH, DHº = +119 Example: Calculate feasibility of the reaction: CH3–OH + H–I CH3–I + H–OH ∆H° = ?? Bond Dissociation Energy Tables ∆G° = ∆H° - T ∆S° ∆H° = (sum of strength of bonds broken) – (sum of strengths of bonds made) Recall: 7/29/2015 © Univesity of California 3 First ten entries in --------------------------------------- name freq rank MARY 1 PATRICIA 2 LINDA 3 BARBARA 4 ELIZABETH 5 JENNIFER 6 MARIA 7 SUSAN 8 MARGARET 9 DOROTHY 10 JAMES 1 JOHN 2 ROBERT 3 MICHAEL 4 WILLIAM 5 DAVID 6 RICHARD 7 CHARLES 8 JOSEPH 9 THOMAS 10 CH3–OH + H–I CH3–I + H–OH 93 71 57 119 164 – 176 = –12 kcal mol-1 To functionalize alkanes, we need to break C H But: Are all C–H bonds the same ? DHº s decrease along the series: CH4 > Rprim―H > Rsec―H > Rtert―H No! Primary .
