The atoms/groups which are more charge on them and withdraw the electrons of the carbon chain towards themselves are known to exert-I Effect (pronounced as "minus I effect") electronegative than carbon gain a slight negative The atoms/groups which are more electropositive than carbon gain a slight positive charge on them and push the electrons of the carbon chain away from themselves are known to exert +I Effect (pronounced as "plus I effect") The atoms/groups in which lone pair(or electrons of negative charge) is in conjugation with double or triple bond are electron donating and gain a formal positive charge in the resonating structure in the process and are known to exert +M/+R Efect. The atoms/groups which are in conjugation with double or triple bond and are electron withdrawing and gain a formal negative charge in the resonating structure in the process and are known to exert -M/-R Effect.