1. When an electrophile such as W approaches an alkene molecule, the π electrons are instantaneously shifted to the electrophile and a new bond is formed between carbon and hydrogen. This makes the other carbon electron deficient and hence it acquires a positive charge.
2. When the it electron is transferred towards the attacking reagent, it is called positive electromeric (+E) effect.
3. Whèn the t electron is transferred away from the attacking reagent it is called negative electromenc (-E) effect.
For example : The attack of CN⊖ on a carbonyl carbon.
