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Organic Chemistry 4 th Edition Paula Yurkanis Bruice. Chapter 16 Reactions of Substituted Benzenes. Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall. Examples of Substituted Benzenes. The relative positions of the two substituents are

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slide1

Organic Chemistry

4th Edition

Paula Yurkanis Bruice

Chapter 16

Reactions

of

Substituted Benzenes

Irene Lee

Case Western Reserve University

Cleveland, OH

©2004, Prentice Hall

slide3

The relative positions of the two substituents are

indicated by numbers or by prefixes

slide5

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

slide8

The incorporated substituent is given the 1-position; the

ring is numbered in the direction that yields the lowest

possible number

slide14

The same reagent that oxidizes the alkyl substituent will

oxidize the alcohol

Therefore, a milder oxidizing reagent is used:

slide15

Reduction of a Nitro Substituent

It is possible to selectively reduce just one nitro group

slide17

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

slide19

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

slide21

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

slide22

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

slide25

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

slide27

These substituents are powerful electron-withdrawing

groups

These substituents withdraw electrons both inductively

and by resonance

slide28

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

slide29

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
slide33

Electron withdrawal decreases reactivity toward

electrophilic substitution and increases acidity

Electron donation increases reactivity toward electrophilic

substitution and decreases acidity

slide35

Methoxy and hydroxy substituents are so strongly

activating that halogenation is carried out without Lewis

slide38

In designing a disubstituted benzene, the order in which

the substituents are to be placed on the ring must be

considered

slide45

A strongly activating substituent will win out over a

weakly activating substituent or a deactivating substituent

slide52

The Arenediazonium Ion as an Electrophile

Only highly activated benzene rings can undergo this

reaction

Substitution takes place preferentially at the para position

slide61

The electron-withdrawing substituents must be ortho or

para to the site of nucleophile attack

The electrons of the attacking nucleophile can be

delocalized

slide68

1-substituted naphthalenes are easier to form

2-substituted naphthalenes are more stable

slide69

In substituted naphthalenes, the nature of the substituent determines which ring will undergo electrophilic substitution

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