Question

what is I and R effect in chemistry?

Answer 1

Hey friend

here is your answer

In most of the cases, resonance effect is stronger and outweighs inductive effect.

For example, the -OH and -NH2 groups withdraw electrons by inductive effect (-I). However they also release electrons by delocalization of lone pairs (+R effect). Since the resonance effect is more stronger than inductive effect the net result is electron releasing to rest of the molecule. This is clearly observed in phenol and aniline, which are more reacting than benzene towards electrophilic substitution reactions.

Whereas the inductive effect is stronger than the resonance effect in case of halogen atoms. These are electronegative and hence exhibit -I effect. However at the same time they also release electrons by delocalization (+R effect) of lone pair.

This is evident in case of reactivity of halobenzenes, which are less reactive than benzene towards electrophilic substitution due to -I effect of halogens.

But it interesting to note that the substitution is directed at ortho and para positions rather than meta position. It can be ascribed to the fact that the electron density is increased at ortho and para positions due to +R effect of halogens as shown below.

Thanks

don't forget to mark as braintlist answer