Return to Contents Chapter 8: Nucleophilic Substitution Ch 8 contents

Reaction of Alcohols with Hydrogen Halides
(review of chapter 4)

Substitution of alcohols using HX

Reaction type: Nucleophilic Substitution (SN1 or SN2)

Summary:

SN1 MECHANISM FOR REACTION OF ALCOHOLS WITH HBr
 

Step 1:
An acid/base reaction. Protonation of the alcoholic oxygen to make a better leaving group. This step is very fast and reversible.  The lone pairs on the oxygen make it a Lewis base. 
 
 
 

Step 2:
Cleavage of the C-O bond allows the loss of the good leaving group, a neutral water molecule, to give a carbocation intermediate. This is the rate determining step (bond breaking is endothermic) 
 
 
 
 

Step 3:
Attack of the nucleophilic bromide ion on the electrophilic carbcation creates the alkyl bromide. 
 
 
 
 
 
 


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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary