OWLS: Electrophilic Aromatic Substitution Solutions - UCLA

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4. (c) (d) (e) (f) (g) H 3C OCH 3 H OSO 3H or O NH 2 Cl CH 3 SO 3 H 2SO 4 Cl AlCl 3 NO 2 benzene aq. HONO 2 aq. H 2SO 4 HO 3S AlCl 3 1. NaNO 2, aq. HCl 2. PhOH H 3C H 3C OWLS: Electrophilic Aromatic Substitution Solutions 4 CH 3O O 2N O N NO 2 Consider arenium ion stability plus steric effects. N OH H OSO 3H 5. In each case, electrophilic attack on the aromatic ring gives the more stable arenium ion. Draw all of the resonance contributors if necessary to convince yourself. (a) aq. HONO 2 aq. H 2SO 4 NO 2
(b) (c) OCH 3 SO 3 H 2SO 4 OWLS: Electrophilic Aromatic Substitution Solutions 5 OCH 3 The major product choice is based on the assumption that a benzene ring offers more steric hindrance than a methoxy group. O + CH 3 O Cl AlCl 3 6. Remember that Ph = phenyl = C 6H 5 = monosubstituted benzene ring. 7. O N O H OH 2 O N OH H OH 2 Ph NH2 N O Ph N N O Ph N Ph N N OH Ph N N OH H OH 2 NH 2 CH 3 excess Br 2 H NH 2 Br Br CH 3 O O CH 3 SO 3H H OH 2 O N OH2 O N + OH 2 H OH 2 H N O H OH 2 Ph N H N OH Ph N N OH2 Ph N N Ph N N excess CH 3I K 2CO 3 N(CH 3) 3 Br Br Br The NH 2 and CH 3 (electron-donating) substituents of 4-methylaniline give its benzene ring enough nucleophilicity so that it can react with Br 2 in the absence of a Lewis acid catalyst such as FeBr 3. The reactivity is also enhanced by the increased stability imparted to the arenium ion by the NH 2 and CH 3 groups. Potassium carbonate is a weak base that is necessary to convert all of the amine to the ammonium salt. (Work out the mechanism to see how this happens.) Other weak bases could also be used. Bromination must be conducted before alkylation because the R 3N + substituent is a meta directing group. When there are multiple directing groups on the benzene ring, the strongest electron donor dominates. (In this case a methyl group is a stronger electron donor than an ammonium group, which is not an electron donor at all! For more on this concept ask Dr H for the EAS Supplemental Reading.) CH 3
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OWLS: Electrophilic Aromatic Substitution Solutions - UCLA

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