Mesomeric Effect | Easy Trick of Mesomeric Effect | Organic Chemistry

Summary

This video explains the mesomeric effect, a special type of resonance where functional groups donate or withdraw electrons through resonance in conjugated systems. The script walks through the concept of resonance, its importance, and how different functional groups, such as hydroxyl or aldehyde, exhibit positive or negative mesomeric effects. It contrasts mesomeric effect with inductive effect, describing how electron donation or withdrawal happens in various compounds. The video concludes with practical tips for identifying the effects in organic compounds, using a simple trick to differentiate positive and negative mesomeric and inductive effects.

Takeaways

• 😀 Resonance is the possibility of shifting Pi electrons within a molecule, resulting in different resonance structures.
• 😀 Mesomeric effect is a special case of resonance, where resonance involves a functional group (the 'sister') donating or withdrawing electrons.
• 😀 In mesomeric effect, if resonance occurs between two brothers (carbon atoms) and a sister (functional group), it is called mesomeric effect.
• 😀 Functional groups that donate electrons through resonance are known as positive M effect (e.g., hydroxyl group).
• 😀 Functional groups that withdraw electrons through resonance are known as negative M effect (e.g., aldehyde group).
• 😀 Conjugated systems, which contain alternating single and double bonds, are essential for resonance and mesomeric effects.
• 😀 Positive M effect happens when a functional group donates electron pairs through resonance, while negative M effect occurs when the functional group withdraws electrons.
• 😀 Inductive effect is different from mesomeric effect: it refers to the shifting of electron density due to the electronegativity of atoms or groups.
• 😀 Positive I effect involves electron-releasing groups (e.g., alkyl groups), while negative I effect involves electron-withdrawing groups (e.g., functional groups).
• 😀 To determine the effect in an organic compound, consider the presence of lone pairs and the electronegativity of the atoms or groups involved.

Q & A

What is resonance in organic chemistry?

Resonance refers to the possibility of shifting Pi electrons in a molecule, which creates different structures known as resonance structures. These structures represent alternative electron distributions within a molecule.

What is the mesomeric effect?

The mesomeric effect is a special case of resonance that occurs when a functional group either donates or withdraws electrons through resonance in a conjugated system. This effect impacts the distribution of electrons in the molecule.

What is the difference between mesomeric effect and resonance?

While resonance refers to the overall shifting of Pi electrons within a molecule, mesomeric effect specifically occurs when a functional group is involved in donating or withdrawing electrons through resonance in a conjugated system.

How can the mesomeric effect be explained using an analogy?

An analogy used to explain the mesomeric effect involves three brothers exchanging a football (representing Pi electrons). If resonance occurs between two brothers and a sister, the effect is called mesomeric. The 'sister' represents a functional group in this analogy.

What conditions are necessary for resonance to occur?

For resonance to occur, a molecule must have a conjugated system, meaning alternating single and double bonds that allow for the movement of Pi electrons between atoms.

What is the significance of conjugated systems in resonance and mesomeric effects?

Conjugated systems, where single and double bonds alternate, are essential for resonance because they provide the necessary environment for the shifting of Pi electrons. For mesomeric effects, the functional group in the conjugated system must either donate or withdraw electrons.

How do functional groups affect the mesomeric effect?

Functional groups can either donate electrons (positive mesomeric effect) or withdraw electrons (negative mesomeric effect) through resonance in a conjugated system, influencing the overall electron distribution within the molecule.

What is the relationship between mesomeric effect and inductive effect?

The mesomeric effect involves the donation or withdrawal of electrons via resonance, while the inductive effect refers to the shifting of electron density due to electronegativity differences. The mesomeric effect generally dominates over the inductive effect.

What is the significance of electron-donating and electron-withdrawing groups in mesomeric effects?

Electron-donating groups, like hydroxyl (-OH) and amine (-NH2) groups, enhance the electron density in the conjugated system through resonance, contributing to a positive mesomeric effect. Conversely, electron-withdrawing groups, like aldehyde (-CHO) and nitro (-NO2) groups, pull electron density away, causing a negative mesomeric effect.

Can a compound show both mesomeric and inductive effects simultaneously?

Yes, a compound can exhibit both mesomeric and inductive effects, but the mesomeric effect typically dominates. For example, an amine group (NH2) can donate electrons through resonance (positive mesomeric effect) while also withdrawing electrons inductively due to its electronegativity.