Induction Effect

In molecules with covalent polar bonds, i.e. bonds where the difference electronegativity (Δx) is greater than 0.4, partial charges occur. A positive partial charge arises on an atom with a lower electronegativity, a negative partial charge on an atom with a higher electronegativity. In the HCl molecule, therefore, the positive partial charge arises on the hydrogen atom (x = 1), the negative partial charge on the chlorine atom (x = 2.8). The shift of electrons along the σ bond (sigma) is called the 'induction effect. There is a positive and negative induction effect.

Positive induction effect
It occurs when the central atom of the functional group has a lower electronegativity than the carbon inside the chain. A positive induction effect is caused, for example, by the groups -PH2, -SiH3 or -SH.

ethyl mercaptan CH3δδ-←CH2δ-←SHδ+

Negative induction effect
It is caused by the higher electronegativity of the central atom of the group than the carbon inside the chain. Typical examples are halogens (-F, -Cl, -Br, -I), -OH, -NH2 or -NO.

1-chloropropane CH3δδδ+→CH2δδ+→CH2δ+→Clδ-

Source

 * interpretation of the teaching staff of the Ecclesiastical Gymnasium in Pilsen