CHAPTER TWENTY-THREE Aryl Halides 23.5 NUCLEOPHILIC SUBSTITUTION IN NITRO-SUBSTITUTED ARYL HALIDES One group of aryl halides that do undergo nucleophilic substitution readily consists of those that bear a nitro group ortho or para to the halogen OCH NaoCH3 Nacl p-Nitroanisole(92%) Sodium chloride An ortho-nitro group exerts a comparable rate-enhancing effect. m-Chloronitrobenzene, although much more reactive than chlorobenzene itself, is thousands of times less reac- tive than either o-or p-chloronitrobenzene The effect of o- and p-nitro substituents is cumulative, as the following rate data demonstrate Increasing rate of reaction with sodium methoxide in methanol (50C O2N、 Chlorobenzene 1-chloro- 1-chloro- 2-chloro- 4-nitrobenzene 2. 4-dinitrobenzene 1.3, 5-trinitrobenzene Relative rate 1.0 7×10 24×1015 (too fast to measure) PROBLEM 23.2 Write the structure of the expected product from the reaction of 1-chloro-2, 4-dinitrobenzene with each of the following reagen (aCH3 CH2ON (b)CHSCH2 SNa ( d)CH SAMPLE SoLUTION (a)Sodium ethoxide is a source of the nucleophile CH3,O, which displaces chloride from 1-chloro-2, 4-dinitrobenzene OCHCH +CH3CH2O一 NO 1-Chloro-2 4-dinitrobenzene Ethoxide 1-Ethoxy-2, 4-dinitrobenzene Back Forward Main MenuToc Study Guide ToC Student o MHHE Website23.5 NUCLEOPHILIC SUBSTITUTION IN NITRO-SUBSTITUTED ARYL HALIDES One group of aryl halides that do undergo nucleophilic substitution readily consists of those that bear a nitro group ortho or para to the halogen. An ortho-nitro group exerts a comparable rate-enhancing effect. m-Chloronitrobenzene, although much more reactive than chlorobenzene itself, is thousands of times less reac￾tive than either o- or p-chloronitrobenzene. The effect of o- and p-nitro substituents is cumulative, as the following rate data demonstrate: PROBLEM 23.2 Write the structure of the expected product from the reaction of 1-chloro-2,4-dinitrobenzene with each of the following reagents: (a) CH3CH2ONa (b) C6H5CH2SNa (c) NH3 (d) CH3NH2 SAMPLE SOLUTION (a) Sodium ethoxide is a source of the nucleophile CH3CH2O, which displaces chloride from 1-chloro-2,4-dinitrobenzene. Cl NO2 NO2 1-Chloro-2,4-dinitrobenzene CH3CH2O Ethoxide anion OCH2CH3 NO2 NO2 1-Ethoxy-2,4-dinitrobenzene Cl Increasing rate of reaction with sodium methoxide in methanol (50°C) Cl Chlorobenzene Relative rate: 1.0 Cl NO2 1-Chloro- 4-nitrobenzene 7  1010 NO2 Cl NO2 1-Chloro- 2,4-dinitrobenzene 2.4  1015 NO2 Cl O2N NO2 2-Chloro- 1,3,5-trinitrobenzene (too fast to measure) NO2 OCH3 p-Nitroanisole (92%) CH3OH 85°C Cl NO2 p-Chloronitrobenzene NaOCH3 Sodium methoxide NaCl Sodium chloride 922 CHAPTER TWENTY-THREE Aryl Halides Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website