O Chem Question

[tawaqul]

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If donating groups like CH3 stabilize, does this make them (when added to a benzene) more reactive or less reactive?

Because, if something acidic has lots of withdrawing groups (that's what makes it acidic, right?), that means it is destabilized and I have always thought that the less stable something is, the more reactive it is. But apparently, acidic benzenes, which are less stable, are less reactive than basic benzenes...

Is this incorrect???

I'm confusing myself!

 

[Tina324]

hmm can u give an example

 

[nixon13]

Donating groups make the ring more reactive. I have a trick that I use to help me tell if something is donating or withdrawing. Groups such as CH3 and NH2 have the C and N bonded to the ring directly. The hydrogens have a positive charge giving the C and N a negative charge which is donated to the ring making it more reactive. Now a group such as NO2, the N is bonded directly to the ring and the oxygen has a net negative charge making the N positive. This withdraws the electrons from the ring making is less reactive. Withdrawing groups make a ring more acidic where as donating groups make it basic.

 

[tawaqul]

Donating groups make the ring more reactive. I have a trick that I use to help me tell if something is donating or withdrawing. Groups such as CH3 and NH2 have the C and N bonded to the ring directly. The hydrogens have a positive charge giving the C and N a negative charge which is donated to the ring making it more reactive. Now a group such as NO2, the N is bonded directly to the ring and the oxygen has a net negative charge making the N positive. This withdraws the electrons from the ring making is less reactive. Withdrawing groups make a ring more acidic where as donating groups make it basic.

so it is NOT correct to say that just because something is more stable, it will be less reactive and vice versa?

I found another example, kind of related to my confusion with this. I was wondering why tertiary alcohols dehydrate fastest...b/c normally I think a tertiary alcohol is the most stable, which would make it least reactive. Apparently, these must not go together. I just wonder how reactivity and stability are related?

 

[doc3232]

so it is NOT correct to say that just because something is more stable, it will be less reactive and vice versa?

I found another example, kind of related to my confusion with this. I was wondering why tertiary alcohols dehydrate fastest...b/c normally I think a tertiary alcohol is the most stable, which would make it least reactive. Apparently, these must not go together. I just wonder how reactivity and stability are related?

No it IS correct to say that. For example tri-nitro benzene is not reactive at all.
Just like Noble gases are stable and mostly unreactive. Same applies for O-chem. Benzene is quite stable. As long as strong electron donating group are attached, then it becomes more reactive. Otherwise quite stable and quite unreactive.

Hope this helps
doc3232

 

[tawaqul]

No it IS correct to say that. For example tri-nitro benzene is not reactive at all.
Just like Noble gases are stable and mostly unreactive. Same applies for O-chem. Benzene is quite stable. As long as strong electron donating group are attached, then it becomes more reactive. Otherwise quite stable and quite unreactive.

Hope this helps
doc3232

aren't you saying the opposite here, though, b/c e-donating groups stabilize and should make it unreactive? Or is this an exception or something.

 

[tawaqul]

bump for the last question.

 

[Tina324]

you know, i wrote out this whole explanation right now and just deleted it b/c i confused myself. Can someone please help us with this anomaly between reactivity and stability. I know that they don't always occur together...but it doesn't make sense...it might have something to do with the PE diagram i think. dunno...SOS help! lol

 

[tawaqul]

I think I understand that it is simply a RULE now. E- withdrawing groups make things more acidic and acidity decreases reactivity.

So donators stabilize and make things more reactive.

I know it's the opp. of how I usually think about it. But I guess for aromatic compds I'll just memorize this.