Difference Between EDG and EWG

Thekey differencebetween EDG and EWG is that theEDG (stands for Electron Donating Groups) can increase the electron density of a conjugated pi system whereas the EWG (stands for Electron Withdrawing Groups) decreases the electron density of a conjugated pi system.

EDG and EWG are亲电aromaticdirecting groups. Both of these are forms of substituents that we can find in organic compounds.

CONTENTS

1.Overview and Key Difference
2.What is EDG
3.What is EWG
4.Side by Side Comparison – EDG vs EWG in Tabular Form
5.概括

What is EDG?

EDG stands for electron donating groups. We call them “electron releasing groups (ERG)” as well. These are substituents in organic compounds that can donate some of its electron density into a conjugated pi system. This is done via resonance effect orinductive effect。This makes the pi electron system morenucleophilic。

例如，EDG，连接到苯环时，苯环可以进行亲电取代反应。这是因为EDG增加了苯环的电子密度。然而，苯通常经历这种类型的亲电取代反应。因此，EDG可以提高反应速率。因此，我们将这些取代基称为芳香环激活组。EDG的一些示例包括苯并，初级，二元胺，乙醚，苯酚等。

What is EWG?

EWG代表电子撤回组。它与EDG在芳环上具有相反的效果。因此，它从Pi电子系统中去除电子密度。这使PI电子系统更具亲电性。因此，当这些基团附着在苯环上时，它们将降低亲电替代反应的反应速率。

Moreover, EWG can deactivate aromatic rings. This is done via resonance withdrawing effect or inductive withdrawing effect. For benzene, these groups can make the ortho and para positions less nucleophilic. Hence, the benzene ring tends to undergo electrophilic addition reactions at meta positions. Some examples of EWG includes trihalides, sulfonates, ammonium, aldehydes, ketones, esters, etc.

What is the Difference Between EDG and EWG?

EDG stands for electron donating groups while EWG stands for electron withdrawing groups. Both these are “electrophilic aromatic directing groups”. As a key difference between EDG and EWG, we can say that the EDG can increase the electron density of a conjugated pi system whereas the EWG decreases the electron density of a conjugated pi system. Basically, EDG can donate electrons while EWG can receive electrons. Moreover, EDG can increase the nucleophilicity of aromatic rings, which is the opposite function of EWG; it decreases the nucleophilicity of aromatic rings. Both these substituents show significant effects on the electrophilic substitution reactions of conjugated pi systems such as benzene ring; EDG can increase the reaction rate of electrophilic substitution reactions of aromatic rings whereas EWG can decrease the reaction rate of electrophilic substitution reactions of aromatic rings.

The below infographic lists out more details on the difference between EDG and EWG.

概括– EDG vs EWG

Both EDG and EWG are electrophilic aromatic directing groups. They show opposite functions when attached to aromatic rings. Therefore, we can denote the key difference between EDG and EWG as; EDG can increase the electron density of a conjugated pi system whereas EWG decreases the electron density of a conjugated pi system.

Reference:

1. Hunt, Ian R. “Ch12: Substituent Effects.” Ch 13 – NMR Basics.Available here
2. “Electrophilic Aromatic Directing Groups.” Wikipedia, Wikimedia Foundation, 11 July 2018.Available here

Image Courtesy:

1.”Nitrobenzene resonance”By Ed (Edgar181) – Own work, (Public Domain) viaCommons Wikimedia