In elimination reactions, two groups or atoms or atoms attached to adjacent carbon atoms in a molecule are removed and multiple bond is formed between the two carbon atoms. It is usually called β -elimination. Sometimes both the atoms or groups are eliminated from the same carbon atom in the molecule. It is then called α -elimination. There are three types of mechanism involved in elimination reactions. In E 1 mechanism, carbonium ion is formed by slow

ionization of the substrate. Then the carbonium ion is attacked by the strong base in the fast step to form alkene. In E 2 mechanism, proton removed from the β -carbon and the leaving of the group from α -carbon take place simultaneously. In E 1 cb mechanism, the proton is removed from β -carbon of the substrate molecule from the anion formed, alkene is obtained by the slow step by the departure of the leaving group. The structure of alkene is predicted by Saytzeff's and Hofmann rules.

(i)When 1-nitro-2-bromobutane is subjected to dehydrobromination. The major product is –