Wanzlick equilibrium

This assertion was based on reactivity studies which they believed showed that the free carbene reacted with electrophiles (E-X).

The dimer (a substituted tetraaminoethylene) was believed to be inactive to the electrophiles (E-X), and thought to merely act as a stable carbene reservoir.

The free carbene could then either re-dimerise, regenerating the tetraaminoethylene starting material, or react with E-X (as Wanzlick originally predicted), with either route eventually giving the same reaction product, the dihydroimidazolium salt.

These studies led Böhm & Herrmann to conclude in 2000 that "the Wanzlick equilibrium between a tetraaminoethylene and its corresponding carbene did exist".

[12] Others subsequently showed that unhindered diaminocarbenes form dimers by acid-catalysed dimerisation as shown in the Lemal.

Wanzlick's proposed mechanism for the reaction of dihydroimidazol-2-ylidene with electrophiles
Dimer cross-over experiment
Lemal's mechanism for the reaction of tetraaminoethylene with electrophiles. In conditions of excess E-X, the salt (blue) is formed. In conditions of catalytic E-X, the dimer (purple) will be formed. However, this is based on the assumption that the dimer is more stable than the carbene; but this assumption has been questioned. [ 6 ] E-X may be an acid or even a metal salt e.g. LiCl .