To 3: The third method - the direct hydrocyanation - was also developed by Du Pont. The first step, HCN addition to butadiene, gives a mixture of isomers of pentene nitriles and methylbutene nitriles, which is then isomerized predominantly to 3- and 4-pentene nitriles. In the second step, adiponitrile is formed from the anti-Markovnikov addition of HCN: