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Electrophilic Substitution

Electrophilic Substitution. Three Important things to learn for this chapter. Benzene ring is electron rich – so attractive to electrophiles (things which are looking for electrons - +ve charge). How to make a positive X. If benzene is already substituted

alexa-ratliff
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Electrophilic Substitution

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  1. Electrophilic Substitution Three Important things to learn for this chapter • Benzene ring is electron rich – so attractive to electrophiles • (things which are looking for electrons - +ve charge) • How to make a positive X • If benzene is already substituted • (a) where will the second substituent go to • (b) will the substitution be faster or slower than benzene itself • .

  2. How to make a positive X X = Br Br2 + FeBr3 (section 16.1, Fig 16.2) X = Cl Cl2 + FeCl3 (section 16.2 p 550) X= NO2 …. (section 16.2 p 552) X = SO3H …. (section 16.2, p 553) X = CH3, C2H5 (alkyl) …. (section 16.3, p 555) X = COCH3 (acyl) …..(section 16.3, p 558) Classwork 16.4, 16.5, 16.6

  3. If benzene is already substituted • (a) where will the second substituent go to • (b) will the substitution be faster or slower than benzene itself • . (a) Ortho-directing Para-directing Meta-directing (b) Deactivating – ring less electron rich Activating – ring more electron rich Summary Activating – electron donating – ortho and para directing Deactivating – electron withdrawing – meta directing Exception – halogens – deactivating – but ortho and para directing

  4. Explanation (section 16.5) 1. Inductive effect – s bond - electronegativity –short range (1-2 bonds) 2. Resonance effect – through p bonds – long range (many bonds) Two models for explaining 1. Stability of the carbocation intermediates (textbook) 2. Resonance structures of the starting benzene ring (here) • Summary • -OH, -OR, -NH2 inductive - e-withdrawing < resonance – e-donating • CH3 hyperconjugation • Carbonyl C=O inductive e-withdrawing+resonance e-withdrawing • Halides inductive e-withdrawing~resonance e-donating Classwork Work out for And 16.43, 16.41 Homework 16.42, 16.44, 16.45, 16.49, 16.50

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