Advices For Studying Organic Chemistry

6.11 A MECHANISM FOR THE SN 1 REACTION

A Mechanism for the SN1 Reaction

Reaction:

(CH 3 ) 3 CCl + 2 H 2 O acetone (CH 3 ) 3 COH + H 3 O+ + Cl−

Mechanism:
Step 1

C

CH 3

CH 3

CH 3

slow

H 2 O C

CH 3

H 3 C Cl −

CH 3

+ +

Aided by the polar solvent

achlorinedepartswith

the electron pair that

bonded it to the carbon.

Cl

This slowstepproducesthe relatively stable

3 carbocation and a chloride ion. Although

not shown here,theionsare slovated (and

stabilized) by water molecules.

o

Step 2

+ OH

H

OH

H

fast C +

CH 3

H 3 C

CH 3

C

CH 3

H 3 C

CH 3

+

A water molecule acting as a Lewis

base donates an electron pair to the

carbocation (a Lewis acid). This gives

the cationic carbon eight electrons.

The product is a

tert-butyloxonium

ion (orprotonated

tert-butyl alcohol).

Step 3

A water molecule acting as a

Bronstedbaseacceptsa proton

from the tert-butyloxonium ion.

The products are tert-butyl

alcohol and a hydronium ion.

+ OH

H

OH OH +

H

+ OH

H

fast C + H

CH 3

H 3 C

CH 3

C

CH 3

H 3 C

CH 3

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