CHAPTER 23 ARYL HALIDES SOLUTIONS TO TEXT PROBLEMS 23.1 There are four isomers of CH,CI that contain a benzene ring, namely, o, m, and p-chlorotoluene and benzyl chloride CH3 CH CH,CI o-Chlorotoluene m-Chlorotoluene p-Chlorotoluene Benzyl chloride Of this group only benzyl chloride is not an aryl halide; its halogen is not attached to the aromatic ring but to an sp-hybridized carbon Benzyl chloride has the weakest carbon-halogen bond, its measured carbon-chlorine bond dissociation energy being only 293 kJ/mol (70 kcal/mol) Homolytic cleavage of this bond produces a resonance-stabilized benzyl radical CH+ Benzyl chloride Benzyl radical Chlorine aton 23.2 (b) The negatively charged sulfur in C6HSCH2S: Na is a good nucleophile, which displaces SCH,CSH O2 O, 1-Chloro-2.4- Benzyl 2, 4- dinitrobenzene dinitrophenyl sulfide 656 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
CHAPTER 23 ARYL HALIDES SOLUTIONS TO TEXT PROBLEMS 23.1 There are four isomers of C7H7Cl that contain a benzene ring, namely, o, m, and p-chlorotoluene and benzyl chloride. Of this group only benzyl chloride is not an aryl halide; its halogen is not attached to the aromatic ring but to an sp3 -hybridized carbon. Benzyl chloride has the weakest carbon–halogen bond, its measured carbon–chlorine bond dissociation energy being only 293 kJ/mol (70 kcal/mol). Homolytic cleavage of this bond produces a resonance-stabilized benzyl radical. 23.2 (b) The negatively charged sulfur in is a good nucleophile, which displaces chloride from 1-chloro-2,4-dinitrobenzene. Cl NO2 NO2 1-Chloro-2,4- dinitrobenzene SCH2C6H5 NO2 Cl NO2 Benzyl 2,4- dinitrophenyl sulfide C6H5CH2S Na C6H5CH2S Na Benzyl chloride Benzyl radical CH2 Chlorine atom CH Cl 2 Cl Cl CH3 p-Chlorotoluene CH2Cl Benzyl chloride Cl CH3 m-Chlorotoluene CH3 Cl o-Chlorotoluene 656 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARYL HALIDES 657 (c) The nitrogen in ammonia has an unshared electron pair and is nucleophilic; it displaces chloride from 1-chloro-2 4-dinitrobenzene N 1-Chloro-2, 4- 2.4-Dinitroaniline (d) As with ammonia, methy lamine is nucleophilic and displaces chloride NO2 CHANH 1-Chloro-2. 4. N-Methyl- dinitrobenzene 23.3 The most stable resonance structure for the cyclohexadienyl anion formed by reaction of methox ide ion with o-fluoronitrobenzene involves the nitro group and has the negative charge on oxygen 23. 4 The positions that are activated toward nucleophilic attack are those that are ortho and para to the group. Among the carbons that bear a bromine leaving group in 1, 2, 3-tribromo-5-nitrobenzene C-2 satisfies this requirement. Br Br NaOCH, CH isniobahaenoay 23.5 Nucleophilic addition occurs in the rate-determining step at one of the six equivalent carbons of hexafluorobenzene to give the cyclohexadienyl anion intermediate. F+: oc Hexafluorobenzene Methoxide Cyclohexadienyl anion Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
ARYL HALIDES 657 (c) The nitrogen in ammonia has an unshared electron pair and is nucleophilic; it displaces chloride from 1-chloro-2,4-dinitrobenzene. (d) As with ammonia, methylamine is nucleophilic and displaces chloride. 23.3 The most stable resonance structure for the cyclohexadienyl anion formed by reaction of methoxide ion with o-fluoronitrobenzene involves the nitro group and has the negative charge on oxygen. 23.4 The positions that are activated toward nucleophilic attack are those that are ortho and para to the nitro group. Among the carbons that bear a bromine leaving group in 1,2,3-tribromo-5-nitrobenzene, only C-2 satisfies this requirement. 23.5 Nucleophilic addition occurs in the rate-determining step at one of the six equivalent carbons of hexafluorobenzene to give the cyclohexadienyl anion intermediate. Hexafluorobenzene F F F F F F Methoxide ion OCH3 Cyclohexadienyl anion intermediate F F F F F F OCH3 1,2,3-Tribromo- 5-nitrobenzene Br Br Br NO2 1,3-Dibromo-2-ethoxy- 5-nitrobenzene OCH2CH3 Br Br NO2 NaOCH2CH3 CH3O F N O O Cl NO2 NO2 1-Chloro-2,4- dinitrobenzene NHCH3 NO2 NO2 N-Methyl-2,4- dinitroaniline CH3NH2 Cl NO2 NO2 1-Chloro-2,4- dinitrobenzene NH2 NO2 NO2 2,4-Dinitroaniline NH3 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
658 ARYL HALIDES Elimination of fluoride ion from the cyclohexadienyl anion intermediate restores the aromaticity of he ring and completes the reaction. F CF OCH3 Cyclohexadienyl anion 2.3, 4.5, 6-Pentafluoroanisole Fluoride 23.6 4-Chloropyridine is more reactive toward nucleophiles than 3-chloropyridine because the anior intermediate formed by reaction of 4-chloropyridine has its charge on nitrogen. Because nitrogen is more electronegative than carbon, the intermediate is more stable. Y intermediate 23.7 The aryl halide is incapable of elimination and so cannot form the benzyne intermediate necessary for substitution by the elimination-addition pathway 2-Bromo.1.3. 23.8 The aryne intermediate from p-iodotoluene can undergo addition of hydroxide ion at the position meta to the methyl group or para to it. The two isomeric phenols are m-and p-methylphenol NaOH. H,O NaOH. H-O OH m-Methylphenol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
658 ARYL HALIDES Elimination of fluoride ion from the cyclohexadienyl anion intermediate restores the aromaticity of the ring and completes the reaction. 23.6 4-Chloropyridine is more reactive toward nucleophiles than 3-chloropyridine because the anionic intermediate formed by reaction of 4-chloropyridine has its charge on nitrogen. Because nitrogen is more electronegative than carbon, the intermediate is more stable. 23.7 The aryl halide is incapable of elimination and so cannot form the benzyne intermediate necessary for substitution by the elimination–addition pathway. 23.8 The aryne intermediate from p-iodotoluene can undergo addition of hydroxide ion at the position meta to the methyl group or para to it. The two isomeric phenols are m- and p-methylphenol. CH3 OH p-Methylphenol CH3 OH m-Methylphenol CH3 I p-Iodotoluene CH3 NaOH, H2O (elimination phase) NaOH, H2O (addition phase) CH3 Br CH3 2-Bromo-1,3- dimethylbenzene (No protons ortho to bromine; elimination is impossible.) 3-Chloropyridine N Cl Y Anionic intermediate (less stable) N Cl Y 4-Chloropyridine N Cl Y Anionic intermediate (more stable) N Y Cl 2,3,4,5,6-Pentafluoroanisole F F F F OCH3 F Fluoride ion F Cyclohexadienyl anion intermediate F F F F F F OCH3 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARYL HALIDES 659 23.9 The"triple bond"of benzyne adds to the diene system of furan Mg THF 23.10(a) dIb CICHCH (e) (f) O,N 2-Bromo-l-chloro-4. (Note: This compound is not an aryl halide. CHCI ,CI 2-Chloronaphthalene p-Bromobenzyl Cl CI (i) 9-Fluorophenanthrene 23.11 (a) Chlorine is a weakly deactivating, ortho, para-directing substituent CCH AlCI HCcI CH Chlorobenzene o-Chloroacetophenone p-Chloroacetophenone Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
23.9 The “triple bond” of benzyne adds to the diene system of furan. 23.10 (a) (b) (c) (d) (e) ( f ) (g) (h) (i) ( j) 23.11 (a) Chlorine is a weakly deactivating, ortho, para-directing substituent. Chlorobenzene Cl AlCl3 o-Chloroacetophenone Cl CCH3 O Acetyl chloride CH3CCl O p-Chloroacetophenone Cl C O CH3 9-Fluorophenanthrene F 3 2 1 10 9 8 7 6 5 4 1,8-Dichloronaphthalene Cl Cl 1 2 3 5 4 6 7 8 2-Chloronaphthalene Cl 1 2 3 5 4 6 7 8 CH2Cl Br p-Bromobenzyl chloride ClCHCH3 1-Chloro-1-phenylethane (Note: This compound is not an aryl halide.) Br O2N Cl 2-Bromo-1-chloro-4- nitrobenzene 4,4-Diiodobiphenyl I I 1 1 3 3 2 2 4 4 5 5 6 6 CH CH2 F p-Fluorostyrene OCH3 Br Br 2,6-Dibromoanisole CH3 Cl m-Chlorotoluene F Br Mg, THF heat O O ARYL HALIDES 659 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
660 ARYL HALIDES (b) Bromobenzene reacts with magnesium to give a gri H-Br diethyl ether C6HsMgBr Bromobenzene (c) Protonation of the Grignard reagent in part(b)converts it to benzene C6HSMgBr ChO Benzene bromide (d) Aryl halides react with lithium in much the same way that alkyl halides do, to form organo- lithium reagents. diethyl ether CHI C6HLi lil Iodobenzene Lithium Phenyllithium Lithium (e) With a base as strong as sodium amide, nucleophilic aromatic substitution by the elimination-addition mechanism takes place NaNH NaNH, Bromobenzene Benzyne C) The benzyne intermediate from p-bromotoluene gives a mixture of m-and p-methylaniline H3 NH, p-Bromotoluene 4-Methylbenzyn Methylaniline (g) Nucleophilic aromatic substitution of bromide by ammonia occurs by the addition-elimination NO (h) The bromine attached to the benzylic carbon is far more reactive than the one on the ring and is the one replaced by the nucleophile NaCN CH, Br Bromobenzyl bromide Bromobenzyl cyanide Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(b) Bromobenzene reacts with magnesium to give a Grignard reagent. (c) Protonation of the Grignard reagent in part (b) converts it to benzene. (d) Aryl halides react with lithium in much the same way that alkyl halides do, to form organolithium reagents. (e) With a base as strong as sodium amide, nucleophilic aromatic substitution by the elimination–addition mechanism takes place. (f ) The benzyne intermediate from p-bromotoluene gives a mixture of m- and p-methylaniline. (g) Nucleophilic aromatic substitution of bromide by ammonia occurs by the addition–elimination mechanism. (h) The bromine attached to the benzylic carbon is far more reactive than the one on the ring and is the one replaced by the nucleophile. NaCN p-Bromobenzyl bromide Br CH2Br p-Bromobenzyl cyanide Br CH2CN NH3 1-Bromo-4- nitrobenzene Br NO2 p-Nitroaniline NO2 NH2 NaNH2 NH3 NaNH2 NH3 p-Bromotoluene Br CH3 4-Methylbenzyne CH3 m-Methylaniline NH2 CH3 p-Methylaniline NH2 CH3 NaNH2 NH3 NaNH2 NH3 Bromobenzene Benzyne Br Aniline NH2 diethyl ether Iodobenzene C6H5I Phenyllithium C6H5Li Lithium 2Li Lithium iodide LiI H2O HCl Benzene C6H6 Phenylmagnesium bromide C6H5MgBr diethyl ether Bromobenzene C6H5Br Phenylmagnesium bromide Mg C6H5MgBr 660 ARYL HALIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARYL HALIDES 661 (i) The aromatic ring of N, N-dimethylaniline is very reactive and is attacked by p-chlorobenzene diazonium ion (CH,2N 》+=>c (CH3)2N N, N-Dimethylaniline p-Chlorobenzenediazonium 4-(4-Chlorophenylazo)-N, N-dimethylaniline ( Hexafluorobenzene undergoes substitution of one of its fluorines on reaction with nucleo- philes such as sodium hydrogen sulfide NaSH F F Hexafluorobenzene hydrogen sulfide 3.12 (a) Since the tert-butoxy group replaces fluoride at the position occupied by the leaving group. substitution likely occurs by the addition-elimination mechanism CH OC(CH3) + Ch3)3co OC(CH3)3 o-Fluorotoluene rt-Butoxide tert-Butyl o-methylphenyl (b) In nucleophilic aromatic substitution reactions that proceed by the addition-elimination mechanism, aryl fluorides react faster than aryl bromides. Because the aryl bromide is more reactive in this case, it must be reacting by a different mechanism, which is most likely elimination-addition OC(CH KOC(CH,) DMSO 23.13 (a) Two benzyne intermediates are equally likely to be formed. Reaction with amide ion can occur in two different directions with each benzyne, giving three possible products. They are formed in a 1: 2. 1 ratio H, Ratio: 2 Asterisk(*)refers toc Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(i) The aromatic ring of N,N-dimethylaniline is very reactive and is attacked by p-chlorobenzenediazonium ion. ( j) Hexafluorobenzene undergoes substitution of one of its fluorines on reaction with nucleophiles such as sodium hydrogen sulfide. 23.12 (a) Since the tert-butoxy group replaces fluoride at the position occupied by the leaving group, substitution likely occurs by the addition–elimination mechanism. (b) In nucleophilic aromatic substitution reactions that proceed by the addition–elimination mechanism, aryl fluorides react faster than aryl bromides. Because the aryl bromide is more reactive in this case, it must be reacting by a different mechanism, which is most likely elimination–addition. 23.13 (a) Two benzyne intermediates are equally likely to be formed. Reaction with amide ion can occur in two different directions with each benzyne, giving three possible products. They are formed in a 1:2:1 ratio. Asterisk (*) refers to 14C. NaNH2 NH3 Cl * * * : 1 : NH2 * 2 NH2 * NH2 Ratio: 1 * Bromobenzene Br tert-Butyl phenyl ether OC(CH3)3 Benzyne KOC(CH3)3 DMSO KOC(CH3)3 DMSO tert-Butoxide ion (CH3)3CO o-Fluorotoluene CH3 F F tert-Butyl o-methylphenyl ether CH3 OC(CH3)3 CH3 F OC(CH3)3 Hexafluorobenzene Sodium hydrogen sulfide NaSH F F F F F F 2,3,4,5,6-Pentafluorobenzenethiol SH F F F F F N,N-Dimethylaniline (CH3)2N 4-(4-Chlorophenylazo)-N,N-dimethylaniline (CH3)2N N N Cl p-Chlorobenzenediazonium ion N N Cl ARYL HALIDES 661 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
662 ARYL HALIDES (b) Only one benzyne interme possible, leading to two products in a 1: I ratio Nh t Ratio D refers to H(deuterium) 23. 14(a) o-Chloronitrobenzene is more reactive than chlorobenzene, because the cyclohexadienyl anion intermediate is stabilized by the nitro group CHC1‖ CH3O Comparing the rate constants for the two aryl halides in this reaction reveals that o-chloro- nitrobenzene is more than 20 billion times more reactive at 50%C (b) The cyclohexadienyl anion intermediate is more stable, and is formed faster, when the electron-withdrawing nitro group is ortho to chlorine o-Chloronitrobenzene reacts faster than m-chloronitrobenzene. The measured difference is a factor of approximately 40,000 at 50.C (c) 4-Chloro-3-nitroacetophenone is more reactive, because the ring bears two powerful electron withdrawing groups in positions where they can stabilize the cyclohexadienyl anion CHO CH O CI CH O CI (d) Nitro groups activate aryl halides toward nucleophilic aromatic ution best when they to the leavi is more reactive than 2-Fluoro-1, 3 I-Fluoro-3,5. Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(b) Only one benzyne intermediate is possible, leading to two products in a 1:1 ratio. D refers to 2 H (deuterium). 23.14 (a) o-Chloronitrobenzene is more reactive than chlorobenzene, because the cyclohexadienyl anion intermediate is stabilized by the nitro group. Comparing the rate constants for the two aryl halides in this reaction reveals that o-chloronitrobenzene is more than 20 billion times more reactive at 50°C. (b) The cyclohexadienyl anion intermediate is more stable, and is formed faster, when the electron-withdrawing nitro group is ortho to chlorine. o-Chloronitrobenzene reacts faster than m-chloronitrobenzene. The measured difference is a factor of approximately 40,000 at 50°C. (c) 4-Chloro-3-nitroacetophenone is more reactive, because the ring bears two powerful electronwithdrawing groups in positions where they can stabilize the cyclohexadienyl anion intermediate. (d) Nitro groups activate aryl halides toward nucleophilic aromatic substitution best when they are ortho or para to the leaving group. is more reactive than 2-Fluoro-1,3- dinitrobenzene F O2N NO2 1-Fluoro-3,5- dinitrobenzene O2N NO2 F CH3O Cl C N CH3 O CH3O Cl N O C CH3 CH3O Cl C N CH3 O O O O O O O CH3O Cl N O O O CH3O Cl N O D Cl D D NH2 D NH2 D NaNH2 NH3 D same as Ratio: 1 : 1 662 ARYL HALIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARYL HALIDES 663 (e) The aryl halide with nitro groups ortho and para to the bromide leaving group is more reactive than the aryl halide with only one nitro group NO N is more reactive than NO I-Bromo-2.4. 1.4-Dibromo-2. dinitrobenzene nitrobenzene 23.15(a)The nucleophile is the lithium salt of pyrrolidine, which reacts with bromobenzene by an elimination -addition mechanism Br LiN LiBr Lithium rved yield, 84%) (b) The nucleophile in this case is piperidine. The substrate, 1-bromo-2, 4-dinitrobenzene, is ver reactive in nucleophilic aromatic substitution by the addition-elimination mechanism. NO, 1-Bromo-2, 4- Piperidine N-(2, 4-Dinitrophenyl)- dinitrobenzene (c) Of the two bromine atoms, one is ortho and the other meta to the nitro group. Nitro groups activate positions ortho and para to themselves toward nucleophilic aromatic substitution, and so it will be the bromine ortho to the nitro group that is displaced. Br 1. 4.Dibromo-2 Piperidine N-(4 23. 16 Because isomeric products are formed by reaction of 1-and 2-bromonaphthalene with piperidine at elevated temperatures, it is reasonable to conclude that these reactions do not involve a common Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(e) The aryl halide with nitro groups ortho and para to the bromide leaving group is more reactive than the aryl halide with only one nitro group. 23.15 (a) The nucleophile is the lithium salt of pyrrolidine, which reacts with bromobenzene by an elimination–addition mechanism. (b) The nucleophile in this case is piperidine. The substrate, 1-bromo-2,4-dinitrobenzene, is very reactive in nucleophilic aromatic substitution by the addition–elimination mechanism. (c) Of the two bromine atoms, one is ortho and the other meta to the nitro group. Nitro groups activate positions ortho and para to themselves toward nucleophilic aromatic substitution, and so it will be the bromine ortho to the nitro group that is displaced. 23.16 Because isomeric products are formed by reaction of 1- and 2-bromonaphthalene with piperidine at elevated temperatures, it is reasonable to conclude that these reactions do not involve a common 1,4-Dibromo-2- nitrobenzene Br Br NO2 Piperidine N H N-(4-Bromo-2-nitrophenyl)- piperidine Br NO2 N 1-Bromo-2,4- dinitrobenzene Br NO2 NO2 Piperidine N H N-(2,4-Dinitrophenyl)- piperidine NO2 NO2 N Bromobenzene Br LiBr Lithium pyrrolidide LiN N-Phenylpyrrolidine (observed yield, 84%) N is more reactive than 1,4-Dibromo-2- nitrobenzene NO2 Br Br 1-Bromo-2,4- dinitrobenzene Br NO2 NO2 ARYL HALIDES 663 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
664 ARYL HALIDES intermediate and hence follow an addition-elimination pathway. Piperidine acts as a nucleophile and substitutes for bromine on the same carbon atom from which bromine is I-Bromonaphthalene Piper 2-Bromonaphthalene Piperidine Compound B When the strong base sodium piperidide is used, reaction occurs by the elimination-addition pathway via a"naphthalyne" intermediate. Only one mode of elimination is possible from 1-bromo- Br This intermediate can yield both A and B in the addition stage B Two modes of elimination are possible from 2-bromonaphthalene addition addition Compounds A and B Compound B only Both naphthalyne intermediates are probably formed from 2-bromonaphthalene because there is no reason to expect el on to occur only in one direction. Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
intermediate and hence follow an addition–elimination pathway. Piperidine acts as a nucleophile and substitutes for bromine on the same carbon atom from which bromine is lost. When the strong base sodium piperidide is used, reaction occurs by the elimination–addition pathway via a “naphthalyne” intermediate. Only one mode of elimination is possible from 1-bromonaphthalene. This intermediate can yield both A and B in the addition stage. Two modes of elimination are possible from 2-bromonaphthalene: Both naphthalyne intermediates are probably formed from 2-bromonaphthalene because there is no reason to expect elimination to occur only in one direction. Br elimination stage Compounds A and B addition stage Compound B only addition stage Compound A N Compound B N sodium piperidide piperidine Br NaBr N H N Na Piperidine N H 2-Bromonaphthalene Br Compound B N 1-Bromonaphthalene Br Piperidine N H Compound A N 664 ARYL HALIDES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARYL HALIDES 665 23.17 Reaction of a nitro-substituted aryl halide with a good nucleophile leads to nucleophilic aromatic substitution Methoxide will displace fluoride from the ring, preferentially at the positions ortho and para to the nitro group. OCH CH-OH 1,2,3 23.18 (a) This reaction is nucleophilic aromatic substitution by the addition-elimination mechanism. SCH,C6Hs NO C6HSCH2SK 4-chloro-3. 4-( Benzylthio)-3- trotoluene The nucleophile, CgHS CHIS:, displaces chloride directly from the aromatic ring. The produc in this case was isolated in 57%o yield (b) The nucleophile, hydrazine, will react with 1-chloro-2, 4-dinitrobenzene by an addition- elimination mechanism as shown H2N--NH2CI HN NO2 NO, t hNNH, -Chloro- 2.4- Hydrazine 4-Dinitrophenyl- dinitrobenzene The nitrogen atoms of hydrazine each has an unshared electron pair and hydrazine is fairly nucleophilic. The product, 2, 4-dinitrophenylhydrazine, is formed in quantitative yield (c) The problem requires you to track the starting material through two transformations. The first of these is nitration of m-dichlorobenzene, an electrophilic aromatic substitution reaction. HNO: m-Dichlorobenzene 2. 4-Dichloro- Because the final product of the sequence has four nitrogen atoms( C6H6N4O4), 2, 4-dichloro- -nitrobenzene is an unlikely starting material for the second transformation. Stepwise Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
23.17 Reaction of a nitro-substituted aryl halide with a good nucleophile leads to nucleophilic aromatic substitution. Methoxide will displace fluoride from the ring, preferentially at the positions ortho and para to the nitro group. 23.18 (a) This reaction is nucleophilic aromatic substitution by the addition–elimination mechanism. The nucleophile, , displaces chloride directly from the aromatic ring. The product in this case was isolated in 57% yield. (b) The nucleophile, hydrazine, will react with 1-chloro-2,4-dinitrobenzene by an addition– elimination mechanism as shown. The nitrogen atoms of hydrazine each has an unshared electron pair and hydrazine is fairly nucleophilic. The product, 2,4-dinitrophenylhydrazine, is formed in quantitative yield. (c) The problem requires you to track the starting material through two transformations. The first of these is nitration of m-dichlorobenzene, an electrophilic aromatic substitution reaction. Because the final product of the sequence has four nitrogen atoms (C6H6N4O4), 2,4-dichloro- 1-nitrobenzene is an unlikely starting material for the second transformation. Stepwise Cl NO2 Cl 2,4-Dichloro-1- nitrobenzene Cl Cl m-Dichlorobenzene HNO3 H2SO4 Cl NO2 NO2 1-Chloro-2,4- dinitrobenzene H2NNH2 Hydrazine 2,4-Dinitrophenylhydrazine H2N NO2 NO2 NH H Cl Cl NO2 N O O H2N NH2 C6H5CH2S C6H5CH2SK Cl NO2 CH3 4-Chloro-3- nitrotoluene SCH2C6H5 NO2 CH3 4-(Benzylthio)-3- nitrotoluene NaOCH3 CH3OH NO2 F F F F F 1,2,3,4,5-Pentafluoro- 6-nitrobenzene NO2 OCH3 F F F F 2,3,4,5-Tetrafluoro- 6-nitroanisole NO2 F F OCH3 F F 2,3,5,6-Tetrafluoro- 4-nitroanisole ARYL HALIDES 665 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website