Application of Mesomeric Effect

A large percentage of the carbon, oxygen and nitrogen atoms in organic molecules are not bonded to each other; hence the bond energy within a given molecule is significantly lower than the total bond energy of that molecule. The mechanism of such reactions is called “mesomerism” or “intermolecular dissociation”.

The mesomeric Effect is responsible for adding an electron-donating group to a benzene ring or ketone to favour the cyclic pi bond over the lone pair of electrons on the adjacent carbon atom. The major difference between Inductive And Mesomeric Effect

It is such that resonance interacts with bonds, and mesomeric interacts with the functional group.

Difference Between Inductive And Mesomeric Effect

The inductive Effect and the mesomeric Effect are two electronic effects that can occur in polyatomic molecules. The inductive effect arises due to the polarization of σ bonds. The mesomeric effect can be explained by ortho-para or sigma-pi interactions due to electron-donating or withdrawing elements(functional groups) present in a molecule. Both types of Effect are applicable in some complex molecules, having more than one functional group (not explaining the entire molecule).

Difference Between Inductive And Mesomeric Effect, you will learn how inductive and mesomeric effects are different. Also, their difference in bond polarity, examples of two different molecules of each type and the difference between inductive and mesomeric will be clearly described.

Mesomeric Effect operates in unsaturated compounds with conjugated systems such as aldehydes, ketones, carbanions etc. It operates via an electron pair of π bonds or the lone pair of electrons. The induction occurs due to a slightly displaced electron pair of – bonds in saturated compounds.

Difference Between Mesomeric Effect And Resonance

Resonance and mesomeric Effect are two important chemical concepts that determine the structure of an organic molecule. The resonance results from interactions between lone electron pairs on atoms, whereas the mesomeric Effect arises due to the presence of substituents or functional groups.

The difference between mesomeric Effect and resonance lies in their definitions and causes of occurrence. Resonance and mesomeric effects are two weird quantum chemical phenomena. When a molecule contains lone pairs (of electrons) on some of its atoms, it may have more than one possible structure. The possibilities can be reduced to only one structure using the concepts of resonance and mesomeric Effect.

However, the mesomeric Effect distorts the electron density distributions on the molecule, whereas resonance depends on interactions between bond electrons and lone electron pairs. The interaction may be repulsive or attractive.

In chemistry, two theories are responsible for the stabilization of molecules. These are resonance and mesomeric effects. While resonance affects the polarity of a molecule, the mesomeric Effect has no considerable effect on it. Furthermore, the presence of lone electron pairs at the double bond in a molecule is the cause of resonance. In contrast, electron-donating or withdrawing substituent groups causes the mesomeric Effect.

In chemistry, resonance is a phenomenon that occurs when the charges in the atoms of a molecule become distributed over several atoms so that the molecule has an overall neutral electrical charge. It can occur when the positive charge from one end of the molecule is balanced by a negative charge from the other end. The mesomeric effect refers to certain types of stabilization of molecules having functional groups or different substituent groups on both sides of a double bond. The mesomeric Effect causes these molecules to be bent and not linear.

Examples Of Mesomeric Effect

Given below are various examples of the Mesomeric Effect

1. +M Effect

When a conjugated system increases electron density, then the +M Effect

The substitutes are –NHCOR, -NR₂, -OH, -OR

2.-M Effect 

When Pi bongs get transferred to a group, the density of the conjugated system decreases. It is the – M effect. 

The substitutes are –CN, -SO₃H, -COR, COOR, CONH₂, COOH, etc.

Conclusion

The mesomeric effect is a feature of resonance in pi systems. This Effect will be displayed as the correlation between the delocalized electrons and unshared pairs of electrons that are diffused in the ring—delocalization results when there is significant overlap between these occupied and unoccupied orbitals. As far as the atoms are concerned, substituents result in each bond being attached to two atoms on opposite sides of the ring.

The positive and negative mesomeric effect influences the overall bond energy in conjugated systems. In ethylene, a methyl substituent can function as an electron-withdrawing or electron-donating group, causing a significant change in the electron density.