Question

Draw the product obtained when trans-2-butene is treated first with br2 in ch2cl2, second with nanh2 in nh3, and then finally with h2/lindlar's catalyst.

Answer 1

Trans-2-butene undergoes halogenation to form 2,3-dibromobutane. It then undergoes the Hoffmann elimination to form trans-2-butene. Finally, it undergoes hydrogenation to form butane.

Step-by-step explanation:

When trans-2-butene is treated with Br2 in CH2Cl2, it undergoes a halogenation reaction where the double bond is replaced with two bromine atoms. The product obtained is 2,3-dibromobutane.

When the resulting 2,3-dibromobutane is treated with NaNH2 in NH3, it undergoes an elimination reaction known as the Hoffmann elimination. The product formed is trans-2-butene.

Finally, when trans-2-butene is treated with H2 in the presence of Lindlar's catalyst, it undergoes hydrogenation and produces butane.

Answer 2

In order to do this, you have change the alkene into an alkyne. That is the aim of Br2/CH2Cl2 trailed by NaNH2. The Br2 with form a vic dihalide (3,4-dibromo octane). Adding of NaNH2 will execute two E2 reactions. -NH2 will eliminate an H from carbons 3 and 4. This double elimination will make the alkyne. Then handling the alkyne with H2/Lindlar will form the cis alkene. The final product will be CIS-3-octene.