Alcohols Substitution Dehydration Oxidation

Substituion involves two parts:

1. Leaving Group (LG)

2. Replacement Group - (Nucleophile) N:

Substitution of alcohols is always in acid, because OH^- (hydroxide) is a BAD LG. On the other hand, H₂O, the conjugate acid of OH^-, is a good LG. The acid transforms hydroxide to water, so the substitution can take place.

If the alcohol is 3°, then the carbocation formed will be 3° and stable enough to exist on its own. The oxonium ion formed will autoionize and the substitution can take place. This process is called S_N1:

Because of the dependence of the stability of the carbocation, the order of reactivity is:

3° Alcohols: Most reactive.

2° Alcohols: Medium reactive.

1° Alcohols: Least reactive.

Actually, only the the 3° alcohols react readily @RT and no catalyst. 1° and 2° need with heat and catalysts.