See the comprehensive review on isatin chemistry: http://jbcs.sbq.org.br/imagebank/pdf/v12n3a02.pdf

I suspect that the effect of halide substitution (on the aromatic ring) on the C-3 carbonyl will not be large. Any effect will likely be due to an inductive electron-withdrawing influence imparted by the halide.  From that perspective, a modest enhancement in nucleophilic addition at the carbonyl might be anticipated.

Dear Sameer,

Halides such as F, Cl, Br and I are electron withdrawing groups. When electron withdrawing group is located at C3 of the benzene ring it is expected that the electrophicity of the carbonyl carbon of the indol derivative will be increased and hence the reactions' rates for the synthesis of pirquinozol, talnetant, tacrine, dibucaine, ciclazindol and others from isatins will be enhanced. Electron withdrawing groups can act by resonance or inductive effect depending on the nature of the group.

The extent of the reactivity enhancement is depending on the electron withdrawing group strength (Hammett's sigma value). For example, NO2- and CF3- are more potent than  halides. Thus the reactivity change with halides is expected to be lesser than NO2 or CF3.

Please note, that the withdrawal effect of halides is mixed; they donate electrons by resonance whereas inductivily they withdraw electrons. The sum of the halide's effect is electron withdrawing.

Hoping this will be helpful,

Rafik

Thank you very much Joseph Sloop sir, 

I agree that Halides will impart its minor inductive effect. I am curious to know a exact resonance effect of substituents (other than halides such as nitro or amino group present on benzene ring of isatin) on C3 carbonyl reactivity of isatin.