Q. 9-9-8 P-b - Organic Chemistry (Mcmurry)

Question

Using any alkyne needed, how would you prepare the following alkenes? 

 (b) cis-3-Heptene

Step-by-Step Solution

Answer

Lindlar’s catalyst

It’s the reagent used in the reaction to convert the alkyne to an alkene by hydrogenation when 1 equivalent  When 2 equivalent  is present alkyne converts to alkane.

Formation of cis-3-Heptene

Alkyne hydrogenation to alkene occurs when a less active Lindlar’s catalyst is used which is a finely divided palladium metal with lead acetate and quinoline, an aromatic amine. The hydrogenation occurs with syn stereochemistry.

Reaction with Lindlar’s catalyst

When alkyne reacts with Lindlar’s catalyst then it breaks the three out of one bond and converts alkyne to an alkene by the addition of hydrogen to the atom and forms alkene as shown: