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Electrophiles vs. Nucleophiles

MermaidWonders

Active member
Feb 20, 2018
113
Stupid question here, but why wouldn't it be possible for $C{H}_{3}Cl$ to act as a nucleophile also since it has a nucleophilic site at the chlorine due to it being negatively-polarized when attached to methyl group?
 

Klaas van Aarsen

MHB Seeker
Staff member
Mar 5, 2012
8,780
Stupid question here, but why wouldn't it be possible for $C{H}_{3}Cl$ to act as a nucleophile also since it has a nucleophilic site at the chlorine due to it being negatively-polarized when attached to methyl group?
With the chlorine bound to the methyl group, it's single valence electron is near the methyl group.
Consequently, on the outside of the molecule, the chlorine is slightly positive charged, and attracts an electron.
It makes the molecule as a whole an electrophile.

If the chlorine atom would actually bind a lose electron, it would detach itself and form a $\ce{Cl-}$ ion, which is a nucleophile.
 

MermaidWonders

Active member
Feb 20, 2018
113
With the chlorine bound to the methyl group, it's single valence electron is near the methyl group.
Consequently, on the outside of the molecule, the chlorine is slightly positive charged, and attracts an electron.
It makes the molecule as a whole an electrophile.

If the chlorine atom would actually bind a lose electron, it would detach itself and form a $\ce Cl^-$ ion, which is a nucleophile.
Wait... doesn't the polar bond between C and Cl result in Cl being negatively-polarized?
 

Klaas van Aarsen

MHB Seeker
Staff member
Mar 5, 2012
8,780
Wait... doesn't the polar bond between C and Cl result in Cl being negatively-polarized?
A $\ce{Cl}$ atom on its own is neutrally charged.
When it bonds to $\ce C$, the electron in its outer shell moves to the $\ce C$ atom.
So it's indeed negatively polarized near the $\ce C$-atom, but at the same time it is positively polarized on the other side, which is the outside of the molecule.
Attractions to other particles happen on the outside of the molecule.
 

MermaidWonders

Active member
Feb 20, 2018
113
A $\ce Cl$ atom on its own is neutrally charged.
When it bonds to $\ce C$, the electron in its outer shell moves to the $\ce C$ atom.
So it's indeed negatively polarized near the $\ce C$-atom, but at the same time it is positively polarized on the other side, which is the outside of the molecule.
Attractions to other particles happen on the outside of the molecule.
Ah, I see now. :) So if the whole molecule is an electrophile overall, is there a case where the Cl atom serves as the electrophilic site? It's just that with the problems I've encountered so far, I'm used to seeing the C atom acting as the electrophilic site and Cl the nucleophilic site but never the Cl atom yet....
 

Klaas van Aarsen

MHB Seeker
Staff member
Mar 5, 2012
8,780
Ah, I see now. :) So if the whole molecule is an electrophile overall, is there a case where the Cl atom serves as the electrophilic site? It's just that with the problems I've encountered so far, I'm used to seeing the C atom acting as the electrophilic site and Cl the nucleophilic site but never the Cl atom yet....
A $\ce{Cl}$ atom doesn't (normally) occur on its own. If it does we call it a radical, meaning it will immediately react with anything that comes nearby.

Instead we'll either have a $\ce{Cl2}$ molecule, which is electrophilic.
Or we'll have a $\ce{Cl-}$ ion, which is nucleophilic.
 

MermaidWonders

Active member
Feb 20, 2018
113
A $\ce{Cl}$ atom doesn't (normally) occur on its own. If it does we call it a radical meaning it will immediately react with anything that comes nearby.

Instead we'll either have a $\ce{Cl2}$ molecule, which is electrophilic.
Or we'll have a $\ce{Cl-}$ ion, which is nucleophilic.
Yeah, OK, got it. Thanks!