Mesomeric effect is a phenomenon in organic chemistry that describes the delocalization of electrons through a molecule by resonance. It is also known as the resonance effect.

Application of Mesomeric Effect:
The mesomeric effect has several applications in organic chemistry, including:

1. Strength of acids and bases: The mesomeric effect can influence the strength of acids and bases by stabilizing or destabilizing the resulting ion. For example, a carboxylic acid is a stronger acid than an alcohol due to the mesomeric effect of the carbonyl group that stabilizes the negative charge on the oxygen atom.

2. Dipole moment: The mesomeric effect can affect the dipole moment of a molecule by redistributing the electron density within the molecule. For example, in nitrobenzene, the mesomeric effect of the nitro group increases the dipole moment of the molecule.

3. Bond length: The mesomeric effect can influence the bond length in a molecule by changing the electron density around the bond. For example, in a benzene ring, the mesomeric effect of the pi-electrons leads to shorter carbon-carbon bond lengths than would be expected in a normal alkene.

4. Stability of intermediates: The mesomeric effect can stabilize or destabilize reaction intermediates in organic reactions. For example, in the electrophilic aromatic substitution reaction, the mesomeric effect of substituents on the aromatic ring can stabilize the intermediate carbocation, leading to a faster reaction.

In conclusion, the mesomeric effect has a wide range of applications in organic chemistry, including its influence on the strength of acids and bases, dipole moment, bond length, and stability of intermediates.