9. MESOMERIC EFFECT
• The mesomeric effect in chemistry is a property of substituents or functional groups in a
• The effect is used in a qualitative way and describes the electron withdrawing or releasing
properties of substituents based on relevant resonance structures and is symbolized by the
• The mesomeric effect is negative (–M) when the substituent is an electron-withdrawing
group and the effect is positive (+M) when the substituent is an electron releasing group.
• +M EFFECT ORDER :
–O− > –NH2 > –NHR > –OR > –NHCOR > –OCOR > –Ph > –F > –Cl > –Br > –I
• -M EFFECT ORDER :
–NO2 > –CN > --S(=O)2−OH > –CHO > –C=O > –COOCOR > –COOR > –COOH > –CONH2 >
10. INDUCTIVE EFFECT
• The inductive effect is an experimentally observed effect of the transmission of
charge through a chain of atoms in a molecule, giving rise to a permanent dipole
in a bond.
• It is present in a σ bond as opposed to electromeric effect which is present on a
• All halides are electron withdrawing groups, and all alkyl are electron donating.
• If the electronegative atom is then joined to a chain of atoms, usually carbon, the
positive charge is relayed to the other atoms in the chain. This is the electron-
withdrawing inductive effect, also known as the
• However, some groups, such as the alkyl group, are less electron-withdrawing
than hydrogen and are therefore considered as electron-releasing. This is
electron-releasing character and is indicated by the