ALLYLIC CARBON – BENZYLLIC CARBON – VINYLLIC CARBON.

ALLYLIC CARBON – BENZYLLIC CARBON – VINYLLIC CARBON.

Let’s break down the difference between Allylic, Benzylic, and Vinylic carbons — important concepts in organic chemistry, especially in understanding reactivity and stability of molecules.

1. Allylic Carbon

Definition:

An allylic carbon is a carbon atom that is adjacent to a carbon-carbon double bond (C=C).

Structure:

$$\text{C=C–C}\text{(Allylic carbon is the single-bonded carbon next to the double bond)}$$

Example:

• In propene (CH₂=CH–CH₃), the CH₃ carbon is allylic.

Properties:

• Allylic positions are more reactive due to the possibility of resonance stabilization of intermediates (like allylic carbocations or radicals).

2. Benzylic Carbon

Definition:

A benzylic carbon is a carbon atom that is directly attached to a benzene ring, and is not part of the ring itself.

Structure:

C6H5–CH2–R(The CH₂ is benzylic)\text{C}_6\text{H}_5–CH_2–R \quad \text{(The CH₂ is benzylic)}C6​H5​–CH2​–R(The CH₂ is benzylic)

Example:

• In toluene (C₆H₅–CH₃), the CH₃ group contains a benzylic carbon.

Properties:

• Highly reactive due to resonance stabilization from the aromatic ring.

• Benzylic carbocations, radicals, and anions are all resonance stabilized.

3. Vinylic Carbon

Definition:

A vinylic carbon is a carbon atom that is directly involved in a double bond (C=C).

Structure:

$$\text{C=C}\text{(Both carbons are vinylic)}$$

Example:

• In ethene (CH₂=CH₂), both CH₂ groups contain vinylic carbons.

Properties:

• Less reactive toward many substitution reactions.

• Vinylic carbocations are not resonance stabilized, so they are less stable.

Comparison Table:

Would you like me to show resonance structures or reaction examples for each type?

ALLYLIC CARBON – BENZYLLIC CARBON – VINYLLIC CARBON.

Haloalkanes and Haloarenes

CHEM 109A – Organic Chemistry

Chapter 17 Allylic and Benzylic Reactivity