Question

What is +I and - I effect?

Answer 1

-I Effect

When an electronegative atom, such as a halogen, is introduced to a chain of atoms (generally carbon atoms), the resulting unequal sharing of electrons generates a positive charge which is transmitted through the chain.

This causes a permanent dipole to arise in the molecule wherein the electronegative atom holds a negative charge and the corresponding effect is called the electron withdrawing inductive effect, or the -I effect.

+I Effect

When a chemical species with the tendency to release or donate electrons, such as an alkyl group, is introduced to a carbon chain, the charge is relayed through the chain and this effect is called the +I Effect