有机化学 Organic chemistry 2010 For Undergraduates in biological science 王俊儒张继文袁茂森 应用化学系416,417室 87092187(0) By Junru Wang Email:wangjr07@163.com
Organic Chemistry,6h Edition L.G.Wade,Jr. Chapter 7 Alkyl Halides:Nucleophilic Substitution and Elimination By Junru Wang Email:wangjr07@163.com
Content Preparation and physical properties Nucleophilic substitution Factors affecting SN2 versus SN1 reactions ■Elimination Elimination versus substitution Reactions of alkyl halides Organometallic reactions
Key Notes Nucleophilic Substitution ●SN1 ●SN2 ■Elimination(E1,E2) ■Nucleophilicity .The rate of the SN2 reaction increases with the nucleophilic strength of the incoming nucleophile. .The rate of the SN1 reaction is unaffected by the nature of the nucleophile ■Leaving group
Classes of Halides Alkyl:Halogen,X,is directly bonded to sp3 carbon. Vinyl:X is bonded to sp2 carbon of alkene. Aryl:X is bonded to sp2 carbon on benzene ring.Examples: HH H H-C-C-Br C-C HH H alkyl halide vinyl halid aryl halide
Classes of Alkyl Halides Methyl halides:only one C,CH3X Primary:C to which X is bonded has only one C-C bond. Secondary:C to which X is bonded has two C-C bonds. Tertiary:C to which X is bonded has three C-C bonds
Polarity and Reactivity Halogens are more electronegative than C. Carbon-halogen bond is polar,so carbon has partial positive charge. Carbon can be attacked by a nucleophile. Halogen can leave with the electron pair. H+ HC一CI H chloromethane EPM of chloromethane
Uses of Alkyl Halides" Solvents-degreasers and dry cleaning fluid Reagents for synthesis of other compounds Anesthetic:Halothane is CFCHCIBr CHCla used originally (toxic and carcinogenic) 麻醉剂 >In 1847,the Edinburgh obstetrician James Young Simpson first used chloroform for general anesthesia during childbirth Freons,chlorofluorocarbons or CFC's Freon 12,CF2Cl2,now replaced with Freon 22, CF,CHCI,not as harmful to ozone layer. Pesticides-DDT banned in U.S
Uses of Alkyl Halides" ■杀虫剂、杀灭蚊子（疟疾) DDT1939年后广泛使用（残留高） Srilanka ●1934-1935150万(8万died) ●1963：仅15例 ●1968-1969第二季度60万例 1972:环境保护组织（EPA)废除 ■冷却液和喷气燃料推进剂
B.P&Densities Greater intermolecular forces,higher b.p. Dipole-dipole attractions not significantly different for different halides London forces greater for larger atoms Greater mass,higher b.p. Spherical shape decreases b.p. (CH3)3CBr CH3(CH2)3Br 73C 102°C ■Densities .Alkyl fluorides and chlorides less dense than water. .Alkyl dichlorides,bromides,and iodides more dense than water