Activating/Deactivating group mnemonic?

[eldoctor]

Advertisement - Members don't see this ad

Does anyone know a mnemonic? Or at least have a good way of explaining it so that it seems intuitive? The only ones I ever remember are the halogens since they are opposite of what one would expect. Thanks!

 

[pyzhou]

this should be moved to study Q section

also, anything that can donate an electron is activating (-OR, -NH2, note lone pairs on substituents, and -R due to benzene > Carbon in electronegativity, thus pulls e- into the ring)

anything that pulls electrons away is deactivating (-CF3, F draws e-through C, then C becomes partial + charged, and draws from benzene, same applies for -NO2, -COR, COOH, etc etc)

halogens are what you said

does that work?

 

[GigEm91]

It's actually simple.

Activating are Electron Donating groups. These groups have a lone pair atom bonded to the ring. i.e. NH2, OCH3 etc.

Deactivating have an atom with a double bond that is bonded to the ring i.e. C=O, N=O, S=O. groups like NO2, SO3 all have those double bonded groups.


Hope that makes it simpler!

 

[Prateek]

Another thing we were taught is this:

When looking at the group attached to a benzene ring, if the first atom is more electronegative than the second one then it's an electron DONATING group and thus an ACTIVATING group
Example: -CH3 (C more EN than H), -O-CH3(O more EN than C), -NH2 (N > H)

If the first atom is LESS electronegative than the second one then it's an electron WITHDRAWING group and thus a DEACTIVATING group
Example: -NO2 (O > N), -SO3 (O > S), -COOH (O > C), etc.

This rule seems to work for almost any group

 

[Rabolisk]

The rule fails notably for NH3+ derivatives. In NH2, nitrogen has a lone pair to donate, but in NH3+, the positive nitrogen has a strong tendency to pull electrons from the benzene ring.

 

[Prateek]

The rule fails notably for NH3+ derivatives. In NH2, nitrogen has a lone pair to donate, but in NH3+, the positive nitrogen has a strong tendency to pull electrons from the benzene ring.

Well of course the rule isn't going to be 100% proof especially when charges come into play 👎

 

[Erbium]

Way late to the game here... but isn't -NH2 also problematic because it forms complexes with Lewis Acid Catalysts thereby deactivating the ring? Struggling with a post-lab write up because of this.

 

[Cawolf]

That's why you should convert it to an amide before reacting an aniline derivative under acidic conditions.

 

[itsallgood92]

It's actually simple.

Activating are Electron Donating groups. These groups have a lone pair atom bonded to the ring. i.e. NH2, OCH3 etc.

Deactivating have an atom with a double bond that is bonded to the ring i.e. C=O, N=O, S=O. groups like NO2, SO3 all have those double bonded groups.


Hope that makes it simpler!

GigEm91's explanation is probably the easiest way to understand this. The way I learned it was: if you can delocalize electrons away from the ring (i.e. a conjugated system is formed with the ring, such as a molecule containing a double bond, then it is considered to be deactivating or "electron withdrawing" (because it can pull electrons away from the ring). In contrast, an activating group donates its electron density to the ring and usually does not form a conjugated system with the ring, as with any alkane groups attached to a benzene ring

 

[newbeginnings]

Way late to the game here... but isn't -NH2 also problematic because it forms complexes with Lewis Acid Catalysts thereby deactivating the ring? Struggling with a post-lab write up because of this.

Are EAS listed on the aamc mcat outline? I thought we didn't need to know activating/donating groups for benzenes for the new mcat..

 

[Cawolf]

No, this a five year old thread.