Chapter 16 Notes PDF

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Chapter 16 Notes

Ethers, Epoxides, Sulfides

Structure and Properties    

C-O-C bond bent bond, slightly polar no H-bonding (low bp), but H-bond acceptor (slightly water-soluble) crown ethers - specific complexing agents for cations

Nomenclature IUPAC: alkoxy- substituent common: alkyl ether diethyl ether = ethyl ether = "ether" cyclic ethers have special names (and lots of different names) o epoxides (3-membered rings) : oxirane, epoxyalkane, alkene oxide o oxetane (4), oxoloane (5), oxane (6)  sulfides ( C-S-C bond ) o IUPAC uses alkylthio- substituent o common uses alkyl sulfide  disulfides: ( C-S-S-C bond )    

Preparations of Ethers  Williamson synthesis o SN2 reaction of alkoxide with alkyl halide o alkyl halide should be CH3 or 1°  dehydration of alcohols o for symmetrical ethers only, best with CH3 or 1° Preparations of Sulfides  Williamson synthesis with thiolate anion + alkyl halide  double displacement with Na2S and alkyl halide (symmetrical sulfides only)

Reactions of Ethers  generally unreactive towards oxidation, reduction, base, and most acids (make good solvents) EXCEPT for  cleavage by conc. HI or HBr R-O-R + 2 HX ---> 2 R-X + H2O reaction is either SN1 or SN2 (or both), depending on the R groups  radical autoxidation to form hydroperoxides Reactions of Sulfides  similar to ethers except S is a better nucleophile and leaving group and S is easily oxidized  sulfoxide ( S=O bond ) , sulfone ( two S=O bonds )  sulfonium ions (trivalent S+) Preparations of Epoxides  oxidation of alkenes by peroxyacids  internal SN2 in halohydrins

Reactions of Epoxides  unlike most other ethers, epoxides are reactive, because of ring strain  acid-catalyzed ring opening o protonation makes ring opening easier o always backside attack by nucleophile (like SN2) o but nucleophile attacks more substituted carbon (like SN1)  nucleophilic ring opening o direct attack without protonation requires a strong nucleophile o backside attack on less-hindered carbon (like SN2)...