The kinetic product in a reaction is the product formed faster due to a lower activation energy barrier, often under conditions such as low temperature where the reaction is irreversible and does not reach equilibrium. This contrasts with the thermodynamic product, which is more stable but forms slower and predominates under reversible, higher temperature conditions

General Mechanism for Formation of the Kinetic Product (Example:

1,2-Addition in α,β-Unsaturated Carbonyl Compounds)

1. Protonation Step:
   The electrophile (e.g., H⁺ from HX) protonates the alkene or carbonyl compound at the position that leads to the most stable carbocation intermediate (often a tertiary or resonance-stabilized carbocation). This step is fast and forms the carbocation intermediate.

2. Nucleophilic Attack:
   The nucleophile (e.g., Br⁻ in HBr addition) rapidly attacks the carbocation at the position closest to the positive charge, forming the kinetic product. This attack is faster at the site where the nucleophile is in close proximity (ion- pair effect), often leading to 1,2-addition products.

3. Product Formation:
   The product formed is the kinetic product, characterized by addition at adjacent carbons (1,2-addition), which forms faster but may be less stable than the thermodynamic product.

Key Features of the Kinetic Product Mechanism:

• The carbocation intermediate is formed at the position that yields the fastest formation (lowest activation energy), often a tertiary or allylic carbocation.
• The nucleophile attacks before any rearrangement or resonance stabilization can occur.
• The reaction conditions favor irreversibility (low temperature), preventing equilibration to the more stable product.
• The product is often a 1,2-addition product in conjugated systems, formed faster due to proximity and ion-pair effects

Simplified Mechanism Drawing Steps (Example: Addition of HBr to a

Conjugated Diene)

1. Protonation of the diene at the 1-position to form a carbocation at the 2-position (tertiary or allylic carbocation).
2. Immediate nucleophilic attack by Br⁻ at the carbocation site (2-position), yielding the 1,2-addition product (kinetic product).
3. The product is formed faster than any resonance or rearrangement can occur.

This mechanism explains why the kinetic product forms faster and predominates under kinetic control conditions, such as low temperature and irreversible reaction conditions