Advices For Studying Organic Chemistry

A Mechanism for the SN2 Reaction

Reaction:

HO− ++CH 3 Cl CH 3 OH Cl−

Mechanism:

H O − H O H O

δ−

C Cl

HH

H

δ+ δ−

C

HH

H

+

Transtion state

C Cl Cl −

HH

H

δ−

The negative hydroxide ion

pushes a pair of electrons

into the partially positive

carbon from the back side.

The chlorine begins to

move away with the pair of

electrons that have bonded

it to the carbon.

In the transition state, a

bond between oxygen and

carbon is partially formed

and the bond between

carbon and chlorine is

partially broken. The

configuration of the

carbon begins to invert.

Now the bond

between the oxygen

and carbon has

formed and the

chloride has

departed. The

configuration of the

carbon has inverted.

6.8 TRANSIITION STATE THEORY: FREE-ENERGY DIAGRAMS

1. Exergonic and endergonic:
   
   
   1. A reaction that proceeds with a negative free-energy change is exergonic.
   
   
   2. A reaction that proceeds with a positive free-energy change is endergonic.
   
   
   
   


2. The reaction between CH 3 Cl and HO– in aqueous solution is highly exergonic.
   
   
   1. At 60 °C (333 K), ∆G° = –100 kJ mol–1 (–23.9 Kcal mol–1).
   
   
   2. The reaction is also exothermic, ∆H° = –75 kJ mol–1.
   
   
   
   

HO−

+CH 3 Cl CH 3 OH +Cl− ∆G° = –100 kJ mol–1