Question

What does it mean if the Diels alder reaction is a concerted reaction?

Answer 1

Hint: We know that Diels-Alder reaction is a pericyclic reaction. It follows a concerted mechanism. In one single step, all bond breaking and all bond forming takes place. In this reaction, a carbon-carbon triple bond is converted into a double bond. Two new carbon-carbon single bonds are formed. Also, two carbon-carbon double bonds of a conjugated diene are converted into only one double bond.

Complete answer:
In Diels-Alder reaction, an alkene and an alkadiene react to form a cyclic product. Usually six member rings are formed as five member and six member rings are stable due to minimum angle and steric strain. In the Diels-Alder reaction, the conjugated alkadiene is called diene and alkene is called dienophile. This is due to concerted bonding between two separate pi electron entities.
Sometimes, instead of alkene, you can also use alkyne as a dienophile. Diels-Alder reaction, two carbon-carbon pi bonds are broken. During the reaction, four pi electrons of conjugated diene and two pi electrons of dienophile shift. During Diels-Alder reaction, two new carbon-carbon sigma bonds are formed. In other words, during the reaction, two carbon-carbon pi bonds are converted to two carbon-carbon sigma bonds.
The Diels-Alder reaction is a concerted reaction, this means it occurs in only one step. Moreover, all of the atoms that are participating in the reaction form bonds simultaneously. This means that whenever a bridged ring is formed, the substituents bonded to the dienophile are either trans or cis to the bridge.

Note:
Remember that In Diels-Alder reaction, an alkene (dienophile) and an alkadiene (diene) reacts to form a five or six member ring. You can use the Diels-Alder reaction for the production of vitamin B six. You call the reverse reaction as the retro-Diels-Alder reaction. You can use the retro Diels-Alder reaction for industrial manufacture of cyclopentadiene.