[smatik]

I used to check the small amount of Δ+ charge on the carbonyl carbon for deciding the reactivity. If we have and . I know that O is more electronegative than Cl and hence will increase the amount Δ+ on carbonyl carbon more than in the case of Cl also small OH molecule will provide less hinderance than large Cl. So according to me the answer should be but the correct answer is .Can you please explain me how? Thanks

[Sunil Simha]

Have you considered the role of resonance delocalization of electrons from Cl and O?

[smatik]

hmm cl will be a good donor is it O???

[Sunil Simha]

If you remember why Cl is ortho-para directing though it is deactivating (during electrophilic aryl substitution), maybe the same logic applies here too...

[smatik]

well thats because chlorine has three lone pairs of electron which go into resonance with delocalized pi electrons of benzene which increase the amount of Δ- charge on ortho and para positions but in this case if chlorine does so its nucleophillic reactivity of carbonyl carbon will decrease.
BUT Phenol is more ortho and para directing than chlorobenzene(Due to resonance) which means the Δ- charge developed in case of ch3cooh is more than that in case of ch3cocl and hence carbonyl carbon of ch3cocl becomes more favorite site for a nucleophillic attack. Thanks for the discussion..very useful and i got my answer

[Sunil Simha]

Well in addition to what you have said Cl has a stronger inductive effect than resonance effect and hence the net result is pulling away of electron toward itself, unlike oxygen.