what is the effect of velectron withdrawing and donating groups on different organic compounds

Electron withdrawing groups (EWG) have very much affinity towards electrons. When such a group is present in a molecule then most of the charge density will be partially shifted towards EWG. Eg. In nitromethane , EWG present is present and it is Nitro group(NO2) . In this molecule NO2 has partial negative charge since it attracts the charge density towards it's side. CH3 has partial positive charge since it suffers from partial loss of charge density.

The case of electron donating groups(EDG) is quite different. Alkyl groups , alkoxy groups belong to this category. In the case of toluene ( methyl group is attached to benzene) the methyl group present is electron donating. It donates the electron density to benzene ring.

The directing nature of EWG and EDG are different in aromatic substitution reactions. If we consider the electrophilic substitution reactions of substituted benzene, we can see that EWG like NO2 deactivates the ring and leads to meta product. For example , nitration of nitrobenzene gives mainly metadinitrobenzene .But this is not the case if the substituent present were EDG.

EDG substituent activates benzene to electrophilic aromatic substitution and ortho or para substituted product is formed.

For example nitration of toluene will give ortho nitro toluene and paranitro toluene.