What Are the Effects of Carboxyl Groups on Electron Distribution?

[pink_ele]

what are electron withdrawing groups?
please give any important advice to solve questions based on it concept.

 

[opuktun]

I like to think electron withdrawing groups as "thirsty suckers". They suck the electrons out of the ring... due to their electronegativity nature.

Take a look at many examples of ewd and electron donating group. You will see the difference. :) Just a pointer to help you: check the bond mulitiplicity in each case. You will find that unsaturated bond exist mostly in one of them.

 

[pink_ele]

thank you

 

[girimani]

can you tell me whether -OH (hydroxyl group) is electron withdrawing or electron releasing group ?

 

[opuktun]

electron withdrawing

 

[girimani]

is phenol acidic due to the presence of an electron withdrawing group .ie -OH group?

 

[Ygggdrasil]

Phenol is acidic because the negative charge formed from deprotonating the -OH is stabilized by resonance with the aromatic ring.

Whether something is electron withdrawing or electron donating is somewhat context dependent. While -OH acts as an electron withdrawing group when it is attached to an alkyl chain, -OH acts as an electron donating group when attached to an aromatic system (such as in the case of phenol). In the case of aromatic molecules, the lone pair gets donated into the aromatic system, which outweighs the electron withdrawing effect from oxygen's electronegativity.

 

[skc]

If OH on a benzene ring is actually an EDG (activating), why is it a strong acid in the meta position, and a weak acid in the para position. I understand activiting groups are O/P directing- I just don't see why OH would enhance the acidity of a benzene ring at all, if it is in fact an EDG.

 

[opuktun]

When we are discussing about meta/ortho/para positioning, we need a reference point.

What is the functional group on benzene that OH is taken with respect to?

 

[skc]

Sorry about that, its a Carboxyl group. CO2H