slide1
Download
Skip this Video
Download Presentation
Aryl Halides - Bonding, Physical Properties and Reactions

Loading in 2 Seconds...

play fullscreen
1 / 24

Aryl Halides - Bonding, Physical Properties and Reactions - PowerPoint PPT Presentation


  • 149 Views
  • Uploaded on

Aryl Halides - Bonding, Physical Properties and Reactions Nucleophilic Aromatic Substitution of Chlorobenzene Nucleophilic Aromatic Substitution: Addition-Elimination. What’s the Difference Between Ar- and Ph-?. Bonding in Aryl Halides. Aryl Halides.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Aryl Halides - Bonding, Physical Properties and Reactions' - asasia


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1
Aryl Halides - Bonding, Physical Properties and Reactions

Nucleophilic Aromatic Substitution of Chlorobenzene

Nucleophilic Aromatic Substitution: Addition-Elimination

slide4

Aryl Halides

Aryl halides are halides in which the halogen is attached directly to an aromatic ring.

Carbon-halogen bonds in aryl halides are shorter and stronger than carbon-halogen bonds in alkyl halides.

slide5

H2C

CHX

sp2

452 (108)

368 (88)

sp2

469 (112)

406 (97)

X

Dissociation Energies of Selected Compounds

Bond Energy:kJ/mol (kcal/mol)

X = H

X = Cl

sp3

410 (98)

339 (81)

slide6

Resonance Picture

C-X bonds in aryl halides have more double bond character than C-X bonds in alkyl halides

slide8

Preparation of Aryl Halides

Halogenation of arenes (Section 12.5)

electrophilic aromatic substitution

slide10
resemble alkyl halides

are essentially insoluble in water

less polar than alkyl halides

Cl

Cl

 2.2 D

 1.7 D

Physical Properties of Aryl Halides

slide12

Reactions Involving Aryl Halides

Electrophilic aromatic substitution (Section 12.14)

halide substituents are ortho-para directing & deactivating

slide13

Substitution Reactions Involving Aryl Halides

Nucleophilic substitution on chlorobenzene occurs so slowly that forcing conditions are required.

slide14

Nucleophilic Substitution of Chlorobenzene

This reaction does not proceed via SN2……..

slide15
the SN2 is not reasonable because the aromatic ring blocks back-side approach of the nucleophile. Inversion is not possible.

Why is Chlorobenzene Unreactive?

slide16

SN1 Also Unlikely:

Aryl Cations are Highly Unstable

SN1 not reasonable because:

C—Cl bond is strong; therefore, ionization to a carbocation is a high-energy process

aryl cations are highly unstable

slide17

SN1 Reaction is Possible with Very

Powerful Leaving Groups such as Dinitrogen

This is a unique case: halides are not good enough leaving groups for this process to occur.

slide21

1.0

7 x 1010

2.4 x 1015

too fast to measure

The More Electron-Deficient the

Haloarene, the Faster the Substitution

slide23

Kinetics of Nucleophilic Aromatic Substitution

follows second-order rate law:

rate = k [aryl halide] [nucleophile]

inference:

both the aryl halide and the nucleophile are involved in rate-determining step

slide24
Reaction Rate Depends on X: I > Br > Cl > F

Effect of Leaving Group Upon Rate of SN2

During SN2 reactions, the C-X bond breaks during the rate-determining step

C-F (485 kJ/mol), C-Cl (327 kJ/mol)

C-Br (285 kJ/ml, C-I (213 kJ/mol)

ad