Elimination Reactions

E1cB Mechanism

The base abstracts a proton from the alkyl halide resulting in a carbanion which is the conjugate base of the alkyl halide and in the next step the negative charge forms a π-bond pushing out the leaving group. This is termed as E1cB (E1 conjugate base).

1. Less common because the anion formed is so unstable that it breaks down as the proton is being removed.
2. A two step process.
3. E1cB is favored if the anion is stabilized and has a poor leaving group and a strong base is used.

Nitro group stabilizes the carbanion and the PhO group is a poor leaving group.

• –OH is a bad leaving group.
• Anion formed  is stabilized ( aromatic 14 electron system)
• Rare example of a –OH as leaving group(without protonation)