How to differentiate between nucleophilic addition reaction and electrophilic addition reaction?

[jasoncurious]

Hi there!

 

As long as I can remember, an addition reaction consists of both an electrophile and nucleophile. Everytime, the nucleophile is "the one attacking" and the electrophile is "the one attacked". If nucleophilic addition reaction is named in such a way that the reaction is initiated by a nucleophile (it attacks), then electrophilic addition reaction must be occurring in such a way that the electrophile is the one that initiates the reaction.

 

My question is, how does an electrophile initiate an addition reaction when it's always "attacked"?

 

Thank you.

[CarbonCopy]

Everytime, the nucleophile is "the one attacking" and the electrophile is "the one attacked".

 

Not necessarily. What you are taking about is nucleophillic addition reaction and not addition in general.

In electrophillic add reaction, this is reversed. In this case the substrate ( the one being attacked ) is the one that is nucleophillic and the electrophille is the reagent ( the attacker ).

For eg, -C=C- is a nucleophillic center ( so it is substrate ) which can give electrons to an electrophile ( reagent ), like H+, and this adds to the double bond. This is nucleophillic addition.

But, in a C=O group, the carbon is an electrophillic center due to action of oxygen. So, a nucleophile adds to it. This is nucleophillic add.

Edited April 1, 2013 by CarbonCopy

[hypervalent_iodine]

Not necessarily. What you are taking about is nucleophillic addition reaction and not addition in general.

In electrophillic add reaction, this is reversed. In this case the substrate ( the one being attacked ) is the one that is nucleophillic and the electrophille is the reagent ( the attacker ).

For eg, -C=C- is a nucleophillic center ( so it is substrate ) which can give electrons to an electrophile ( reagent ), like H+, and this adds to the double bond. This is nucleophillic addition.

But, in a C=O group, the carbon is an electrophillic center due to action of oxygen. So, a nucleophile adds to it. This is nucleophillic add.

 

I would disagree with this. If something is 'attacked' we are really talking about the movement of electrons. Since the negatively charged electrons will always attack positively charged centres, you would never say that an electrophile is the substrate doing the attacking.