Electromeric Effect
Electromeric Effect (E Effect)
Electromeric effect is a temporary effect which operates in unsaturated molecules containing >C=C< and >C=O, etc. group in the presence of an attacking reagent. The electrometric effect is denoted by letter 'E'.
Electromeric effect is of two types-
1. Positive Electromeric Effect (+E)
2. Negative Electromeric Effect(−E)
1. Positive Electromeric Effect (+E)
When the π electron is transferred towards the attacking reagent, it is called positive electrometric effect (+E Effect).
When an electrophile (E+) approaches an alkene (>C=C<) molecule, the π electrons are instantaneously shifted to the electrophile and a new bond is formed between carbon atom and electrophile consequently other carbon atom aquires +ve charge.
2. Negative Electromeric Effect (−E)
When the π electron is transferred away from the attacking reagent, it is called negative electrometric effect (−E Effect).
The attack of Nu– on a carbonyl carbon is an example of –E effect.
When a nucleophile (Nu−) approaches the carbonyl compound (>C=O), the π electrons between C and O is instantaneously shifted to the more electronegative atom oxygen consequently carbon atom aquires +ve charge and thus facilitating the formation of a new bond between the incoming nucleophile and the carbonyl carbon atom.