Ch 6 - alkyl halides

Ch 6 - Alkyl Halides
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Unformatted text preview: 6 Al kyl Halides: N ucleoph i l Ic Su bstitutIon and E l i m i ¡aTIo¡ 6-1 I ntrod uction 212 Our study of organic chemIstry Is organized Into fam¡lies of compounds classiFed by theIr functional groups. ¢n this chapter, we consIder the propertIes and reactions of alkyL halIdes£ We use theIr reactions to Introduce substItution and elImInatIon¤ two of the most important types of reactions In organIc chemistry¥ Stereochemistry (Chapter 5) wiL¦ p¦ay a major ro¦e In our study of these reactIons. Many other reactions show sImI- larItIes to substItution and elImination, and the techniques Introduced in thIs chapter wIll be used throughout our study of organic reactions£ There are three major classes of organoha¦ogen compounds: the a¦kyL ha¦ides§ the vInyl halIdes¨ and the aryl halIdes© An alkyl halide sImply has a ha¦ogen atoª bonded to one of the sp 3 hybrid carbon atoms of an alkyl group£ A vinyl halide has a haLogen atom bonded to one of the sp 2 hybrId carbon atoms of an alkene£ An aryl halide has a halogen atom bonded to one of the sp 2 hybrId carbon atoms of an aromatIc Ring£ The chemistry of vInyl haLides and «Ryl halIdes Is di¬erent from that of alkyl ha¦ides because their bondIng and hybrIdIzation are di¬erent­ We consIder the reactions of vinyl ha¦ides and aryL halIdes in ¦ater chapters. The s®ructures of some representatIve a¦ky¦ halides, vInyl halIdes, and aryl halIdes are shown here¯ with theIr most common names and uses. Alkyl haLideS CHCl3 CHC°±2 CC¦3 ²CH3 C±3 ³ CHClBr chlorofoRm Freon-22 ® 1 , 1 ¡ L¢trich£oroethane Ha£othane solvent refrIgeraNt cleaNI¤g fl uId noNflammable anesthetIc VinYl halides C \ / H ± " / ± C=C C=C ´ ' H H ´ ' ± ± vINyl chlorIde monomer for poly( v ¥ nyl ch¦orIde) tetrafluoroethylene §TFE) moNome¨ ©or Teflon ª Ar¡l halideS ( C° Cµ PA«A¬dIch­oroBenzene mothBalls h NH¶ H·- _ · y ¸ ' CH¹² ¢ H²COOH º ¢ thyroxIne thyro¥d hormone 6-2 N o m e n c lat ur e of ALkyL H ali des 213 H ,8+ 8- H "¡ I¢C-Cl , H chlOrOmethane EPM OF chlOrOmethane The carbon£haLogen bond ¤n an aLKyl ha¥¤de ¦s polar because halogen atoms are more eLectronegat¤ve than carbon atoms. Most react¦ons of alKyl haL¦des resuLt from breaK¤ng th¦s po§ar¦zed bond¨ The eLectrostat¦c potent¤aL map of chloromethane (F¦gure 6-1) shows h¤gher electron dens¦ty ©red) around the chLor¤ne atom and reLaª t«vely low electron dens¤ty (blue) around the carbon and hydrogen atoms. The carbon atom has a part¤aL pos¦t¤ve charge, maK¤ng ¤t somewhat eLectroph¤L¦c¨ A nucleoph¦le can attacK th¤s electroph¤L¤c carbon, or the haLogen atom can §eave as a hal¤de ¤on¬ taK­ ¦ng the bond¦ng pa¦r of electrons w¤th ¤t¨ By serv¤ng as a Leav¤ng group¬ the haLogen can be el¦m¦nated fro® the alKyl hal¤de, or ¦t can be repLaced (subst¤tuted for) by a w¤de var¤ety of funct¤onal groups. Th¤s versat¤L¤ty allows alKyl haL¤des to serve as ¤nter®ed¦ates ¤n the synthes¤s of many other funct¦ona¯ groups° ...
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