The removal of two atoms or groups one generally hydrogen (H^(+)) and the other a leaving group (L^(-)) resulting in the formation of unsaturated compound is known as elimination reaction. In E_(1) (elimination) reactions the C-L bond is broken heterolytically (in step 1) to form a carbocation (as inS_(N^(1)) reaction) in which (L^(-)) is lost (rate determining step). The carbocation (in step 2) loses a proton from the beta- carbon atom by a base (nucleophile) to form an alkene. E_(1) reaction is favoured in compounds in which the leaving group is at secondar (2^(@)) or tertiary(3^(@)) Position. In E_(2) (elimination) reactions two sigma bonds are broken and a pi-bond is formed simultaneously.E_(2) reactions occur in one step through a transition state. E_(2) reactions are most common in haloalkanes (particulary 1^(@)) and better the leaving group higher is the E_(2) reaction. In E_(2) reactions, both the leaving groups should be antiplaner. E_(1) cb (Elimination unimolecular conjugate base) reaction involves the removal of proton by a conjugate base (step 1) to produce carbanion which loses a leaving group to form an alkene(step 2) and is a slow step 2-Bromopentane is heated with potassium ethoxide in ethanol. The major product obtained is :