What is the Difference Between EDG and EWG

The terms EDG and EWG are used in organic chemistry to describe how a substituent (an atom or group of atoms) affects the electron density around a molecule. EDG stands for the electron-donating group, while EWG stands for the electron-withdrawing group.

What is the difference between EDG and EWG? EDG Increases electron density in the molecule, while EWG decreases electron density in the molecule.

Key Areas Covered

1. What is EDG  
      – Definition, Features 
2. What is EWG
      – Definition, Features 
3. Similarities Between EDG and EWG
      – Outline of Common Features
4. Difference Between EDG and EWG
      – Comparison of Key Differences
5. FAQ: EDG and EWG
      – Answers to Frequently Asked Questions

Key Terms

EDG, EWG, Electron Donating Group, Electron Withdrawing Group

What is EDG

EDG stands for electron donating group. These groups influence how molecules react. EDG contains electron-rich atoms or functional groups, often with a lone pair of electrons. These lone pairs are ready to be shared with other neighbouring atoms. This act pushes electron density toward the surrounding area, creating a region more susceptible to electron-deficient species (electrophiles).

Figure 1: Electron Donating Group

The structure and the ability to donate electrons determine the strength of the EDG. Strong EDGs, like alkoxide groups (-OMe) and amino groups (-NH₂), are excellent donors, significantly increasing a molecule’s reactivity towards electrophiles. Weaker EDGs, such as alkyl groups (-CH₃), contribute a smaller electron boost.

EDGs also influence the stability of reaction intermediates and the basicity (proton-accepting ability) of nearby functional groups. Applications of electron-donating groups are seen in the pharmaceutical and polymer industries, etc

What is EWG

EWGs (electron-withdrawing groups) are functional groups within a molecule that possess a high affinity for electrons. They are electron vacuums, drawing negative charge towards themselves. This creates a region of positive charge in the surrounding area. This electron-deficient zone becomes a prime target for electron-rich species, known as nucleophiles. Nucleophiles, attracted by the positive charge, readily react with the molecule containing the EWG.

Figure 2: Carboxylic Acid with Multiple Electron-Withdrawing Groups

The structure and electronegativity determine the strength of EWG. Strong EWGs, like nitro groups (-NO₂) and carbonyl groups (C=O), exert a powerful influence, significantly increasing the molecule’s reactivity towards nucleophiles. Weaker EWGs, like halogens (Cl, Br, I), have a more subtle effect.

By placing the EWGs within a molecule, the reactivity of the molecules could be manipulated easily. They can also affect the stability of reaction intermediates (temporary structures formed during a reaction) and the acidity of nearby protons (hydrogen atoms).

Similarities Between EDG and EWG

1. EDG and EWG influence the reactivity of a molecule.
2. Both are specific functional groups within a molecule.

Difference Between EDG and EWG

Definition

• EDGs (electron-donating groups) are functional groups within a molecule that have a tendency to donate electrons, thereby increasing electron density in the molecule. EWGs (electron-withdrawing groups) are functional groups within a molecule that possess a high affinity for electrons.

Function

• EDG increases electron density in the molecule by pushing electron pairs towards surrounding atoms, while EWG decreases electron density in the molecule by pulling electron pairs towards itself.

Reactivity

• While EDG makes the molecule more reactive towards electrophiles (electron-deficient species), EWG makes the molecule more reactive towards nucleophiles (electron-rich species).

Effect on Nearby Group

• EDG generally weakens nearby acidic groups (increases pKa), whereas EWG generally strengthens nearby acidic groups (decreases pKa).

Conclusion

EDGs, like electron-rich donors, push electron density outwards, making the molecule more attractive to electrophiles. In contrast, EWGs act like electron vacuums, pulling electron density towards themselves and creating a positive region that nucleophiles can target. This is the main difference between EDG and EWG.

FAQ: EDG and EWG

1. Is NO₂ an EWG or EDG?

NO₂ (nitrogen dioxide) is an electron-withdrawing group or EWG. For example, NO₂ can deactivate aromatic rings towards electrophilic aromatic substitution, making them less reactive.

2. What is EDG in organic chemistry?

EDG stands for Electron Donating Group. In organic chemistry, it refers to an atom or a group of atoms within a molecule that increases the electron density around a specific area of the molecule.

3. How to tell if EDG or EWG?

To tell if a functional group is an electron-donating group (EDG) or an electron-withdrawing group (EWG), we should consider its effect on nearby electron density. EDGs increase electron density in the molecule, while EWGs decrease electron density.

4. Is alcohol an EDG or EWG?

An alcohol group (-OH) is generally considered an electron-donating group (EDG). This is because the oxygen atom in the hydroxyl group has lone pairs of electrons that can be donated into the conjugated system of a molecule, increasing electron density around the carbon it’s bonded to.

5. Is carbon EWG or EDG?

Carbon (by itself as C) is generally considered a weak electron-donating group (EDG) in organic chemistry.

Reference:

1. “Electron withdrawing group.” Wikipedia. Wikipedia Foundation.
2. “Electron donating group.” Illustrated Glossary of Organic Chemistry. UCLA.

Image Courtesy:

1. “Carboxylic acid with multiple electron-withdrawing groups” By Chem – Libre Texts (CC BY-SA 4.0) via Commons Wikimedia
2. “Complementary selectivity with C-H functionalization reactions” By Iriidium – Own work (CC BY-SA 3.0) via Commons Wikimedia