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Chemsheets AS006 (Electron arrangement)
24/04/2017 AROMATIC CHEMISTRY © A Jul-12
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STRUCTURE OF BENZENE Benzene = C6H6
Its structure was a mystery for many years - until Kekule’s dream.
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STRUCTURE OF BENZENE Problems with Kekule’s structure:
1) C-C bonds are all the same length (between C-C and C=C length). 2) Benzene does not undergo addition reactions readily (e.g. with bromine water). 3) H hydrogenation about 152 kJ mol-1 less than expected. © A Jul-12
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STRUCTURE OF BENZENE
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STRUCTURE OF BENZENE
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HYDROGENATION OF BENZENE
© A Jul-12
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NAMING AROMATIC COMPOUNDS benzenecarboxylic acid
methylbenzene (toluene) chlorobenzene nitrobenzene benzenecarboxylic acid (benzoic acid) © A Jul-12
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NAMING AROMATIC COMPOUNDS
1,3-dimethylbenzene (m-xylene) 4-methyl-1-chlorobenzene 2-hydroxybenzenecarboxylic acid 3,5-dinitrobenzenecarboxylic acid © A Jul-12
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NAMING AROMATIC COMPOUNDS
phenylamine (aniline) 2-phenylbutane phenylethene phenylethanone © A Jul-12
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NAMING AROMATIC COMPOUNDS methyl benzenecarboxylate
phenylethanoate methyl benzenecarboxylate (methyl benzoate) N-phenylethanamide © A Jul-12
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NAMING AROMATIC COMPOUNDS
phenol benzene-1,2-diol 2-nitrophenol 2,4,6-trichlorophenol (TCP) © A Jul-12
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NITRATION Conditions conc HNO3 conc H2SO4 catalyst 50ºC nitrobenzene
© A Jul-12
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NITRATION – ELECTROPHILIC SUBSTITUTION
Formation of electrophile HNO3 + 2 H2SO4 + 2 HSO4- + H3O+ NO2 + nitronium ion Reaction of electrophile with aromatic compound NO2 + NO2 + NO2 -H H + © A Jul-12
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NITRATION Equation (name product) Conditions Mechanism
© A Jul-12
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NITRATION Conditions conc HNO3 conc H2SO4 catalyst 50ºC
2-methylnitrobenzene Conditions conc HNO3 conc H2SO4 catalyst 50ºC © A Jul-12
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NITRATION Uses of nitro compounds: 1) as explosives
2) to make aromatic amines (used to make dyes) 1,3,5-trinitrotoluene TNT © A Jul-12
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FRIEDEL-CRAFTS ACYLATION
aromatic ketone Conditions AlCl3 catalyst © A Jul-12
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FRIEDEL-CRAFTS ACYLATION
WARNING! - do not mix Friedel-Crafts acylation & other acylations (needs AlCl3) Swap H on benzene ring for acyl group Swap H on O/N for acyl group © A Jul-12
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FRIEDEL-CRAFTS ACYLATION
WARNING! - Classic question to test this H replaced is on N not benzene ring. This is NOT Friedel-Crafts acylation! © A Jul-12
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FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
Formation of electrophile O AlCl3 + RCOCl AlCl4 – + R C + acylium ion OR O O O O – R-C-O-AlCl3 + AlCl3 + R-C-O-C-R R C + acylium ion © A Jul-12
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FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION
Reaction of electrophile with aromatic compound + C O R O O C R + C R -H H + Regeneration of catalyst AlCl4 – + H+ AlCl3 + HCl or O O – R-C-O-AlCl3 + H+ R-C-OH + AlCl3 © A Jul-12
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FRIEDEL-CRAFTS ACYLATION
Equation Conditions Mechanism © A Jul-12
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FRIEDEL-CRAFTS ACYLATION
Conditions AlCl3 catalyst © A Jul-12
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