In the E1 reaction, leaving group leaves (taking the bonding electrons) in the first step of the reaction. Notice that the first step of this reaction is the same as the first step of the SN1 reaction. The intermediate formed in this step is a planar carbocation. More substituted carbocations are more stable, so this reaction is faster for more substituted alkyl groups. In the second step of this reaction, a base removes a hydrogen from the carbocation. Notice that the hydrogen is removed from the carbon adjacent to the one with the positive charge, forming a carbon-carbon double bond.