electromeric effect
The electromeric effect is a concept in organic chemistry, particularly in the context of reaction mechanisms. It refers to a temporary effect observed in the distribution of electrons in a molecule when it is subjected to an external electric field, such as during a chemical reaction. Here are some key points about the electromeric effect:
- Nature of the Effect: The electromeric effect involves the complete transfer of a pair of electrons from one atom to another within a molecule. This effect is temporary and occurs only in the presence of a reagent.
- Types of Electromeric Effect:
- Positive Electromeric Effect (+E Effect): Occurs when the electron pair is shifted towards the atom to which the reagent gets attached.
- Negative Electromeric Effect (-E Effect): Happens when the electron pair is shifted away from the atom to which the reagent gets attached.
- Relation to Resonance: The electromeric effect is different from resonance. While resonance is a permanent feature of a molecule and involves delocalization of electrons, the electromeric effect is temporary and occurs only under the influence of an attacking reagent.
- Influence on Reactivity: The electromeric effect plays a significant role in determining the reactivity of organic compounds, particularly in addition reactions to double bonds, like in alkenes and carbonyl compounds.
- Example: A classic example of the electromeric effect is observed in the addition of hydrogen halides to alkenes. The pi electrons of the double bond are completely transferred to one of the carbon atoms, making it temporarily negatively charged and the other carbon positively charged, facilitating the addition of the hydrogen halide.
Understanding the electromeric effect is important for students and researchers in organic chemistry, as it helps explain the behavior of molecules during chemical reactions, particularly how electron distribution affects reactivity and mechanisms.