Advices For Studying Organic Chemistry

A Mechanism for the Reaction

Formation of a Rearranged Alkene During Dehydration of a Primary Alcohol

CCCOH

H

+ HA O

H

H HA

H

R H

R

H

E2 + +

Primary alcohol

(R may be H)

The initial alkene

The primary alcohol initially undergoes

acid-catalyzed dehydration by an E2 mechanism

CC

H

H

R

C

R

H

HA protonation + H + A−

The π electrons of the initial alkene can then be used to form a bond with a

proton at the terminal carbon, forming a secondary or tertiary carbocation.

CC

H

H

R

C

R

H CC

H

H

R

C

R

+ H

A− + H deprotonation H + H A

Final alkene

A different β-hydrogen can be removed from the carbocation, so as to

form a more highly substituted alkene than the initial alkene. This

deprotonation step is the same as the usual completion of an E1

elimination. (This carbocation could experience other fates, such as further

rearrangement before elimination or substitution by an SN1 process.)

+CC

H

H

R

C

R

H CC

H

H

R

C

R

(^)