Electromeric effect refers to a molecular polarizability effect occurring by an intramolecular electron displacement (sometimes called the 'conjugative mechanism' and, previously, the 'tautomeric mechanism') characterized by the substitution of one electron pair for another within the same atomic octet of electrons

What is the Electromeric Effect?
The electromeric effect is a temporary effect observed in organic chemistry, primarily in the context of conjugated systems and polar compounds. It plays a significant role in influencing the reactivity of molecules during chemical reactions.
Definition
- The electromeric effect refers to the shift of electrons in a molecule due to the influence of an attacking reagent, resulting in a temporary polarization of the molecule.
- This effect is observed when an electrophile or nucleophile approaches a double bond or a polar bond, causing a shift of π-electrons towards one end of the molecule.
Types of Electromeric Effect
- Positive Electromeric Effect (+E)
- Occurs when electrons are donated to the attacking reagent.
- Stabilizes the intermediate formed during a reaction, enhancing reactivity.
- Negative Electromeric Effect (−E)
- Involves a withdrawal of electrons from the attacking reagent.
- This can lead to decreased reactivity of the compound.
Importance in Reactions
- The electromeric effect is crucial in electrophilic addition reactions.
- It helps in the formation of more stable carbocation or carbanion intermediates, which are essential for further reactions.
- Affects the regioselectivity and stereochemistry in various organic reactions.
Applications
- Utilized in understanding reaction mechanisms in organic chemistry.
- Plays a vital role in predicting the behavior of compounds in electrophilic aromatic substitution and nucleophilic addition reactions.
In summary, the electromeric effect is a key concept in organic chemistry that helps explain the reactivity and stability of intermediates in various chemical reactions. Understanding this effect is essential for predicting the outcomes of organic reactions.