What does'electron releasing' group means in chemistry?

Question

For example- methyl group is the one.


Please give scientific explanation....

Answer 1

The Inductive effect in chemistry is an experimentally observable effect of the transmission of charge through a chain of atoms in a molecule by electrostatic induction (IUPAC definition). The net polar effect exerted by a substituent is a combination of this inductive effect and the mesomeric effect.

The electron cloud in a σ-bond between two unlike atoms is not uniform and is slightly displaced towards the more electronegative of the two atoms. This causes a permanent state of bond polarization, where the more electronegative atoms has a slight negative charge(δ-) and the other atom has a slight positive charge(δ+).

If the electronegative atom is then joined to a chain of atoms, usually carbon, the positive charge is relayed to the other atoms in the chain. This is the electron-withdrawing inductive effect, also known as the -I effect.

Some groups, such as the alkyl group are less electron-withdrawing than hydrogen and are therefore considered as electron-releasing. This is electron releasing character is indicated by the +I effect.

As the induced change in polarity is less than the original polarity, the inductive effect rapidly dies out, and is significant only over a short distance. The inductive effect is permanent but feeble, as it involves the shift of strongly held σ-bond electrons, and other stronger factors may overshadow this effect.

The inductive effect may caused by some molecules also. Relative inductive effects have been experimentally measured with reference to hydrogen.

Relative strengths of the inductive effect of various molecules


Inductive effects can be measured through the Hammett equation.
[edit]

Applications

* (a) Aliphatic carboxylic acids

The strength of an carboxylic acid depends on the extent of its ionization-the more the ionization, the stronger is the acid. The strength of an acid is denoted by the numerical value of pKa. In aliphatic acids, the electron releasing inductive effect of the methyl group, increases the electron density on oxygen and thus hinders the breaking of the O-H bond, which consequently reduces the ionization.

Greater ionization in formic acid when compared to acetic acid makes formic acid(pKa=3.75) stronger than acetic acid(pKa=4.76). Monochloroacetic acid(pKa=2.82) is stronger than formic acid since the electron-withdrawing effect of chlorine promotes ionization.

* (b) Aromatic carboxylic acids

In benzoic acid, the carbon atoms which are present in the ring are sp2 hybridised.As a result, benzoic acid(pKa=4.20) is a stronger acid than cyclohexane carboxylic acid(pKa=4.87). Also, electron-withdrawing groups substituted at the ortho and para positions, enhance the acid strength.

* (c) Dioic acids

Since the carboxyl group is itself an electron-withdrawing group, the dioic acids are, in general, stronger than their monocarboxyl analogues.


The Polar effect or electronic effect in chemistry is the effect exerted by a substituent on modifying electrostatic forces operating on a nearby 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 a alkoxide anion the presence of the substituent has a stabilizing effect.

Examples of electron withdrawing groups are:

* halogens (F, Cl),
* nitriles CN,
* carboxylic acids COOH

An electron releasing group or ERG releases electrons into a reaction center and as such stabilizes electron deficient carbanions.

Examples of electron releasing groups are:

* alkyl 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.

Answer 2

it is a group that have number of electrons on the outmost level that is more than zero and less than 4, these electrons can be easilly released by this atom to achieve a stable outmost layer of 8 electrons

Answer 3

The Electro-Valence Elements Group.

Answer 4

you're supposed to do your own homework and not ask us to do it for you.