View source for Polar effect

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{{for|polar effect in genetics|polar effect (genetics)}}
==Overview==
The '''Polar effect''' or '''electronic effect''' in [[chemistry]] is the effect exerted by a [[substituent]] on modifying [[electrostatic force]]s operating on a nearby [[chemical reaction|reaction]] center. The main contributors to the polar effect are the [[inductive effect]], [[mesomeric effect]] and the through-space electronic field effect.

An '''electron withdrawing group''' or '''EWG''' draws electrons away from a reaction center. When this center is an electron rich [[carbanion]] or an [[alkoxide]] anion the presence of the substituent has a stabilizing effect.

Examples of electron withdrawing groups are: 
* [[halogen]]s (F, Cl), 
* [[nitrile]]s CN, 
* [[carboxylic acid]]s COOH
* [[carbonyl|carbonyls]] CO
 
An '''electron releasing group''' or '''ERG''' (otherwise called electron donating groups or EDG) releases electrons into a reaction center and as such stabilizes electron deficient [[carbocation]]s.

Examples of electron releasing groups are: 
* [[alkyl]] groups
* [[alcohol]] groups
* [[amine|amino]] groups

The total substituent effect is the combination of the polar effect and the combined steric effects.

In [[electrophilic aromatic substitution]] and [[nucleophilic aromatic substitution]] substituents are divided into activating groups and deactivating groups where the direction of activation or deactivation is also taken into account.

==External links==
* Polar effect definition by the IUPAC [[Gold Book]] [http://www.iupac.org/goldbook/P04709.pdf Link]

[[Category:Physical organic chemistry]]

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