Organic Chemistry 4 th Edition Paula Yurkanis Bruice

1. Organic Chemistry 4th Edition Paula Yurkanis Bruice Chapter 16 Reactions of Substituted Benzenes Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall

2. Examples of Substituted Benzenes

3. The relative positions of the two substituents are indicated by numbers or by prefixes

4. The two substituents are listed in alphabetical order

5. If one of the substituents can be incorporated into a name, that name is used and the incorporated substituent is given the 1-position 2-chlorotoluene ortho-chlorotoluene 4-nitroaniline para-nitroaniline 2-ethylphenol ortho-ethylphenol

6. Some disubstituted benzenes have names that incorporate both substituents

7. Naming Polysubstituted Benzenes

8. The incorporated substituent is given the 1-position; the ring is numbered in the direction that yields the lowest possible number

9. Reaction of Alkyl Substituents

10. The halogen in the benzylic position can be replaced by a nucleophile

11. A halo-substituted alkyl group can undergo elimination

12. Reduction of Unsaturated Substituents

13. Oxidation of the Alkyl Substituent

14. The same reagent that oxidizes the alkyl substituent will oxidize the alcohol Therefore, a milder oxidizing reagent is used:

15. Reduction of a Nitro Substituent It is possible to selectively reduce just one nitro group

17. Donation of electrons through a s bond is called inductive electron donation An alkyl group is more electron donating than hydrogen because of hyperconjugation Withdrawal of electrons through a s bond is called inductive electron withdrawal The NH3 group is more electronegative than a hydrogen

18. A substituent can also donate electrons into the ring by delocalizing its lone-pair electrons

19. Electron withdrawing by resonance occurs when the p electrons from the ring are delocalized onto the substituent Substituents such as CO, CN, and NO2 withdraw electrons by resonance

21. The strongly activating substituents make the benzene ring more reactive toward electrophilic substitution All the strongly activating substituents donate electrons by resonance and withdraw electrons inductively

22. The moderately activating substituents can donate electrons into the ring and away from the ring Overall, they donate electrons by resonance more strongly than they withdraw electrons inductively

24. These substituents are slightly more electron donating than they are electron withdrawing

25. These substituents donate into the ring by resonance and withdraw electrons from the ring inductively They withdraw electrons inductively more strongly than they donate electrons by resonance

26. These substituents withdraw electrons both inductively and by resonance

27. These substituents are powerful electron-withdrawing groups These substituents withdraw electrons both inductively and by resonance

28. The substituent already attached to the benzene ring determines the location of the new substituent All activating substituents and the weakly deactivating halogens are ortho–para directors All substituents that are more deactivating than halogens are meta directors

29. The relative stabilities of the carbocations formed from • the electrophilic substitution of the substituted benzene • determine the preferred reaction pathway • Any substituent that donates electrons inductively is an • ortho–para director • All substituents that donate electrons by resonance are • ortho–para directors

33. Electron withdrawal decreases reactivity toward electrophilic substitution and increases acidity Electron donation increases reactivity toward electrophilic substitution and decreases acidity

34. The ortho–para product ratio decreases with an increase in the size of the substituents

35. Methoxy and hydroxy substituents are so strongly activating that halogenation is carried out without Lewis

36. Aniline and N-substituted anilines do not undergo Friedel–Crafts reaction

37. Aniline cannot be nitrated but tertiary aromatic amines can be nitrated

38. In designing a disubstituted benzene, the order in which the substituents are to be placed on the ring must be considered

43. Synthesis of Trisubstituted Benzenes

44. Steric hindrance makes the position between the substituents less accessible

45. A strongly activating substituent will win out over a weakly activating substituent or a deactivating substituent

46. If the two substituents have similar activating properties, neither will dominate

47. Synthesis of Substituted Benzenes Using Arenediazonium Salts

48. Preparation of the Diazonium Salt

50. Consider the synthesis of para-chloroethylbenzene