chem 125 lecture 69 4/17/08 projected material this material is for the exclusive use of chem 125...

Chem 125 Lecture 694/17/08

Projected material

This material is for the exclusive use of Chem 125 students at Yale and may not

be copied or distributed further.

It is not readily understood without reference to notes from the lecture.

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