Electrophilic addition


by garytse86
Tags: addition, electrophilic
garytse86
garytse86 is offline
#1
Nov11-03, 06:54 AM
P: 310
When ethene undergoes electrophilic addition with bromine water Br2(aq), at the second stage the water reacts with the second carbon,and a hydroxyl group bonds with the carbon across the double bond instead of the bromide ion. Why doesn't water intervene at the first stage, i.e. when the first electrophile bonds with the first carbon atom?
Phys.Org News Partner Chemistry news on Phys.org
Patented research remotely detects nitrogen-rich explosives
Pocket-sized anthrax detector aids global agriculture
Structure of sodium channels different than previously believed
Chemicalsuperfreak
Chemicalsuperfreak is offline
#2
Nov11-03, 10:09 AM
P: 324
Originally posted by garytse86
When ethene undergoes electrophilic addition with bromine water Br2(aq), at the second stage the water reacts with the second carbon,and a hydroxyl group bonds with the carbon across the double bond instead of the bromide ion. Why doesn't water intervene at the first stage, i.e. when the first electrophile bonds with the first carbon atom?
Are you asking why it is a stepwise process? Why water attacks after formation of the bromonium ion? This is because ethylene (not ethene, btw) needs to be activated by the bromine for water to attack.

Or are you asking why there is a bromonium ion instead of a full carbocation?
garytse86
garytse86 is offline
#3
Nov11-03, 10:40 AM
P: 310
Yes like what you have said the reaction has to be started by bromine, so why shouldn't both carbon be bonded to OH-, not just one OH-?

Chemicalsuperfreak
Chemicalsuperfreak is offline
#4
Nov11-03, 12:06 PM
P: 324

Electrophilic addition


Originally posted by garytse86
Yes like what you have said the reaction has to be started by bromine, so why shouldn't both carbon be bonded to OH-, not just one OH-?
Well, for starters, you can't have five bonds to carbon. Which is what would happen if you have a bridged hydroxide ion, which you appear to be suggesting.
garytse86
garytse86 is offline
#5
Nov14-03, 11:15 AM
P: 310
I mean as soon as the bromide ion reacts with the carbon, can't the hydroxide take its place so that no bromide ions join, since the surrounding is all water?
Chemicalsuperfreak
Chemicalsuperfreak is offline
#6
Nov14-03, 01:21 PM
P: 324
Originally posted by garytse86
I mean as soon as the bromide ion reacts with the carbon, can't the hydroxide take its place so that no bromide ions join, since the surrounding is all water?
Understand that it's not the bromide ion, but the bromonium ion, it's an electrophile, it's got a positive charge. Hydroxide is negative, it's nucleophilic, you can exchange it with the bromonium ion, too many valence electrons for starters.


Register to reply

Related Discussions
Electrophilic/Nucleophilic aromatic substitutions Biology, Chemistry & Other Homework 1
Electrophilic Substitution Biology, Chemistry & Other Homework 1
Electrophilic addition, elimination and stuff like that Biology, Chemistry & Other Homework 2
electrophilic addition of bromine Chemistry 1
Help needed with Aryl Carbocation stability and Electrophilic Aromatic Substitution Chemistry 11