Phenol Dissociation: O-H Bond Weaker?

[crays]

Hi, my teacher told me that the oxygen in phenol would be delocalized into the benzene ring's electron and thus, making the O-H bond weaker, thus easing the release of the H proton. But i would like to know, since a benzene consist of 3 double bonds, shouldn't the electrons from the benzene itself already occupied most of the shield, thus making it harder for any other electrons to be joined in? Wouldn't the Oxygen, O's electron be repel if they try to merge into the benzene's electron cloud?

 

[Ygggdrasil]

Try drawing resonance structures for phenol. You'll see that in some of them, the oxygen will have a positive charge and thus want to get rid of its proton. Alternatively, if you draw resonance structures for the phenolate ion, you should see that the negative charge from the oxygen gets delocalized to carbons on the ring.

 

[Blueshift5]

Hello,

Thank you for your question. I am a scientist and I would be happy to provide a response to the content you mentioned.

Firstly, let me clarify that phenol is a molecule that contains a benzene ring with a hydroxyl group (OH) attached to it. The O-H bond in phenol is indeed weaker compared to the O-H bond in a simple alcohol molecule like ethanol. This is because in phenol, the oxygen atom is attached to a benzene ring, which has a delocalized electron system. This means that the electrons in the benzene ring are not localized to a specific bond, but rather spread out over the entire ring. This delocalization of electrons in the benzene ring makes it less reactive and more stable.

Now, coming to your question about the delocalization of the oxygen atom's electrons into the benzene ring's electron cloud. Yes, it is true that the benzene ring's electrons are already occupying most of the space and shielding the nucleus. However, this does not mean that the oxygen atom's electrons will be repelled if they try to merge into the benzene ring's electron cloud. In fact, the oxygen's electrons can easily merge into the electron cloud of the benzene ring, as they are attracted to the positively charged carbon atoms in the ring.

Furthermore, the delocalization of the oxygen's electrons into the benzene ring's electron cloud actually makes the O-H bond weaker, as you mentioned. This is because the delocalization of electrons reduces the effective nuclear charge experienced by the oxygen atom, making it easier for the O-H bond to break and release the H+ ion.

In summary, the delocalization of electrons in the benzene ring does make the O-H bond in phenol weaker, and the oxygen atom's electrons are not repelled when trying to merge into the benzene ring's electron cloud. I hope this explanation helps to clarify your doubts.

Best regards,