Inductive effect:
Inductive effect involves displacement of σ-electrons which forms a covalent bond are seldom shared equally between two atoms. This is due to different electronegativity value. Consequently, electrons are displaced towards the more electronegative atom. This induces a certain degree of polarity in the bond. The more electronegative atom acquires a small negative charge (δ−) and the less electronegative atom acquires a small positive charge (δ+). For example, carbon-chlorine bond, chlorine becomes negative charge with respect to carbon atom. Therefore,
The inductive effect (I-effect) refers to the polarity produced in ma molecule as a result of higher electronegativity of one atom compared to another.
——C—›—C—››—C—›››—C—››››—Cl
The carbon-hydrogen bond is used as a standard. Atoms or groups which lose electron towards carbon atom are said to have +I-effect. Such groups are called electron releasing group. e.g. —CH3, CH3-CH2—, (CH3)2CH—, (CH3)3C—, etc. whereas those atoms or groups of atoms which withdraw electron away from carbon atom are said to have a –I-effect. Such groups are refers to an electron-attracting groups. e.g. —NO2,—F, —Cl, —Br, —OH, C6H5—, —CN, —COOH, —OCH3, etc.