Chem 125 Lecture 694/17/08

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conrotation disrotationMöbius Hückel

21

3

4

5

6

21

3

4

5

6

1

2

3

4

1

2

3

4

O2N

X

O2N

X X

NO2

+ +

Substituent Effects on RateX

NO2

+

(from HONO2/H2SO4)

X Relative Rate (overall)

H [1] Cl 0.03 donation / withdrawal

CH3 25 OH 1000 (or ) e-donation eases

formation of cation intermediates

NO2 6 10-

8(CH3)3N+ 1 10-

8

(or ) e-withdrawal retards formation of cation intermediates

Why is -NO2 e-Withdrawing when -OH is e-Donating?

-NO2 6 10-

8

e-withdrawal retards formation of cation intermediates

-OH 1000 e-donation eases

N

O O

O

HpC

C=C pO-1

0

High HOMO; Good Overlap with Phenyl

Low OMO;Good Overlapwith Phenyl

High HOMO;

Low LUMO;Good Overlapwith Phenyl

OH is a Donor

NO2 is a Acceptor

No Overlap with Phenyl

NO2 isallylic

(willing but not able)

Substituent Effects on Orientation (p. 763)

X

NO2

+

(from HONO2/H2SO4)

X

NO2

++

+ +

HO2N

X

+++

+

H

H

X

+

+ +

NO2

X- Relative Rate (per replaceable H)

H- [1] [1] [1] Cl- 0.0008 0.03 0.13

O2N- 9 10-

8

0.6 10-8 0.03 10-8

H3C- 1 39 46 (CH3)3C- 4 6 72

DirectingActivating

Deactivating

Act

Deact

Deact

(CH3)3N- 3 10-

8

0.6 10-8 + _

ortho meta para

EtOC=O 0.006 0.0006

- 0.003

o/p

m

o/p

“e-donating”

“e-withdrawing”

(steric hindrance)?

Preparation ProblemsNO2

Cl

NO2

Cl2

FeCl3

NO2

Cl

Cl2

FeCl3

(Cl+ FeCl4-)

NH2

Cl

HNO3

H2SO4

OH

Cl

“reduction”

(Zn/HCl?)

H2O

100°C

HONO

(NaNO2/HCl)

N2

Cl

+

diazonium salt

Cl-

or :HalCNNO2

H

Cl

Yale ‘98S

Friedel-Crafts Alkylation (pp. 756-761)

“SN2”

“SN1”

Friedel-Crafts Acylation (pp. 756-761)

Ph-CH2-Rreduction

PrimaryNot

Rearranged!

Nucleophilic Aromatic Substitution (pp. 828-830)

Backwards from SN1 / SN2

H‡ ~ 3 kcal/mol

H‡ > 8 kcal/mol

H‡ ~ 4 kcal/mol

H‡ > 5 kcal/mol

H‡ > 15 kcal/mol

Allylic-Benzylic Reactivity - Cation (pp. 790 SN1)

Allylic Reactivity - Cation (p. 705 kinetic-thermodynamic)

CH3-CH-CH=CH2 CH3-CH=CH-CH2

End of Lecture 69April 17, 2009