Internal Elimination Reaction

Internal/Intramolecular Elimination (E_i) Reaction

E_i is also known as a thermal syn elimination or a pericyclic syn elimination. In this type of elimination reaction, two vicinal (adjacent) substituents on an alkane leave simultaneously via a cyclic transition state to form an alkene in a syn elimination. That's why this reaction is also called pericyclic syn or thermal syn elimination. This type of elimination takes place in the presence of heat only and does not require any reagents.

Internal elimination reaction follows first order kinetics, concerted mechanism where two groups leave simultaneously. Thus, involves a five, or six-membered cyclic transition state.
Rate ∝ [Substrate]
Rate = k [Substrate]

Compounds containing at least one β-hydrogen atom in cis-position shows E_i reaction. Esters, Xanthate esters (Chugaev Elimination), 3° amine oxide undergoes internal elimination reaction upon heating. Cope elimination is also an example of E_i reaction.

Internal Elimination Reaction Mechanism

The elimination must be syn and the atoms coplanar for four and five-membered transition states, but coplanarity is not required for six-membered transition states.

Also read E₁ Reaction | E₂ Reaction | E₁cB Reaction