686 PHENOLS (b) The same principle applies here as in part(a). p-Nitrophenyl acetate reacts faster than m- nitrophenyl acetate(by about 45%) largely because p-nitrophenoxide is less basic and thus a better leaving group than m-nitrophenoxide O O Resonance in p-nitrophenoxide is particularly effective because the p-nitro group is directly conjugated to the oxyanion; direct conjugation of these groups is absent in m-nitrophenoxide (c) The reaction of ethyl bromide with a phenol is an SN2 reaction in which the oxygen of the phe nol is the nucleophile. The reaction is much faster with sodium phenoxide than with phenol, because an anion is more nucleophilic than a corresponding neutral molecule Faster reaction CH Arg: CH2c Br ArOCH, CH3 bi Slower reaction CH ArO: Ch,7Br AroChch,+ B (d) The answer here also depends on the nucleophilicity of the attacking species, which is a pl noxide anion in both reactions ArOCH.Cho The more nucleophilic anion is phenoxide ion, because it is more basic than p-nitrophenoxide )00N More basic: Better delocalization of negative better nucleophile harge makes this les Rate measurements reveal that sodium phenoxide reacts 17 times faster with ethylene oxide in ethanol at 70C)than does its p-nitro derivative (e) This reaction is electrophilic aromatic substitution. Because a hydroxy substituent is more activating than an acetate group, phenol undergoes bromination faster than does phenyl -CCH CCH Resonance involving ester group reduces tendency of oxygen to donate electrons to ring Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website(b) The same principle applies here as in part (a). p-Nitrophenyl acetate reacts faster than m￾nitrophenyl acetate (by about 45%) largely because p-nitrophenoxide is less basic and thus a better leaving group than m-nitrophenoxide. Resonance in p-nitrophenoxide is particularly effective because the p-nitro group is directly conjugated to the oxyanion; direct conjugation of these groups is absent in m-nitrophenoxide. (c) The reaction of ethyl bromide with a phenol is an SN2 reaction in which the oxygen of the phe￾nol is the nucleophile. The reaction is much faster with sodium phenoxide than with phenol, because an anion is more nucleophilic than a corresponding neutral molecule. Faster reaction: Slower reaction: (d) The answer here also depends on the nucleophilicity of the attacking species, which is a phe￾noxide anion in both reactions. The more nucleophilic anion is phenoxide ion, because it is more basic than p-nitrophenoxide. Rate measurements reveal that sodium phenoxide reacts 17 times faster with ethylene oxide (in ethanol at 70°C) than does its p-nitro derivative. (e) This reaction is electrophilic aromatic substitution. Because a hydroxy substituent is more activating than an acetate group, phenol undergoes bromination faster than does phenyl acetate. Resonance involving ester group reduces tendency of oxygen to donate electrons to ring. O O CCH3 O O CCH3  More basic; better nucleophile O Better delocalization of negative charge makes this less basic and less nucleophilic. O2N O ArO ArOCH2CH2O H2C CH2 O  ArOCH2CH3  Br CH Br 2 CH3 H H ArO ArO ArOCH2CH3  Br CH Br 2 CH3 O O O  N O  N O O 686 PHENOLS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website