© www.chemsheets.co.uk A2 019 15-Jul-12 STRUCTURE OF BENZENE Benzene = C6H6 Its structure was a mystery for many years - until Kekule’s dream. 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. © www.chemsheets.co.uk A2 019 15-Jul-12 STRUCTURE OF BENZENE H H C H C C C C H C H H STRUCTURE OF BENZENE http://www.isis.stfc.ac.uk/ HYDROGENATION OF BENZENE Energy (kJ/mol) 152 -360 -240 -208 -120 © www.chemsheets.co.uk A2 019 15-Jul-12 NAMING AROMATIC COMPOUNDS CH3 methylbenzene (toluene) Cl chlorobenzene NO2 nitrobenzene © www.chemsheets.co.uk COOH benzenecarboxylic acid (benzoic acid) A2 019 15-Jul-12 NAMING AROMATIC COMPOUNDS CH3 CH3 1,3-dimethylbenzene (m-xylene) CH3 Cl COOH 4-methyl-1-chlorobenzene COOH OH O2N 2-hydroxybenzenecarboxylic acid NO2 3,5-dinitrobenzenecarboxylic acid © www.chemsheets.co.uk A2 019 15-Jul-12 NAMING AROMATIC COMPOUNDS CH3 NH2 CH2 CH2 CH3 phenylamine (aniline) 2-phenylbutane O CH CH2 phenylethene CH3 C phenylethanone © www.chemsheets.co.uk A2 019 15-Jul-12 NAMING AROMATIC COMPOUNDS O O C O O C CH3 phenylethanoate CH3 methyl benzenecarboxylate (methyl benzoate) O NH C CH3 N-phenylethanamide © www.chemsheets.co.uk A2 019 15-Jul-12 NAMING AROMATIC COMPOUNDS OH OH OH phenol OH OH Cl benzene-1,2-diol Cl NO2 2-nitrophenol 2,4,6-trichlorophenol (TCP) Cl © www.chemsheets.co.uk A2 019 15-Jul-12 NITRATION NO2 + + HNO3 H2O nitrobenzene Conditions conc HNO3 conc H2SO4 catalyst 50ºC © www.chemsheets.co.uk A2 019 15-Jul-12 NITRATION – ELECTROPHILIC SUBSTITUTION Formation of electrophile + HNO3 + 2 H2SO4 NO2 + 2 HSO4- + H3O+ nitronium ion Reaction of electrophile with aromatic compound + NO2 + NO2 H + -H © www.chemsheets.co.uk NO2 A2 019 15-Jul-12 NITRATION CH3 CH3 NO2 Equation (name product) Conditions Mechanism © www.chemsheets.co.uk A2 019 15-Jul-12 NITRATION CH3 CH3 NO2 + HNO3 + H2O 2-methylnitrobenzene Conditions conc HNO3 conc H2SO4 catalyst 50ºC © www.chemsheets.co.uk A2 019 15-Jul-12 NITRATION Uses of nitro compounds: 1) as explosives 2) to make aromatic amines (used to make dyes) CH3 O2N NO2 NO2 1,3,5-trinitrotoluene TNT © www.chemsheets.co.uk A2 019 15-Jul-12 FRIEDEL-CRAFTS ACYLATION R O C O + R C Cl + R HCl O C O + R C O O C O R + R C OH aromatic ketone Conditions AlCl3 catalyst © www.chemsheets.co.uk A2 019 15-Jul-12 FRIEDEL-CRAFTS ACYLATION WARNING! - do not mix Friedel-Crafts acylation & other acylations (needs AlCl3) H H H N R H O R Swap H on benzene ring Swap H on O/N for acyl group for acyl group © www.chemsheets.co.uk A2 019 15-Jul-12 FRIEDEL-CRAFTS ACYLATION WARNING! - Classic question to test this NH2 NHCOCH3 CH3COCl H replaced is on N not benzene ring. This is NOT Friedel-Crafts acylation! © www.chemsheets.co.uk A2 019 15-Jul-12 FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION Formation of electrophile AlCl3 O AlCl4– + RCOCl + R C + acylium ion OR O O AlCl3 + R-C-O-C-R O O – R-C-O-AlCl3 © www.chemsheets.co.uk + R C + acylium ion A2 019 15-Jul-12 FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION Reaction of electrophile with aromatic compound O O C R C + + R H O + C -H R Regeneration of catalyst AlCl4– + H+ AlCl3 + HCl O O – R-C-O-AlCl3 + H+ or R-C-OH + AlCl3 © www.chemsheets.co.uk A2 019 15-Jul-12 FRIEDEL-CRAFTS ACYLATION CH3 CH3 C O CH2CH3 Equation Conditions Mechanism © www.chemsheets.co.uk A2 019 15-Jul-12 FRIEDEL-CRAFTS ACYLATION CH3 CH3 O + CH3CH2 C + Cl HCl C O Conditions CH2CH3 AlCl3 catalyst © www.chemsheets.co.uk A2 019 15-Jul-12