The major product formed in the reaction of cyclopentadiene with a mixture of dichloroacetyl chloride and triethylamine is a Diels-Alder adduct. The Diels-Alder reaction is a type of cycloaddition reaction in which two molecules, one with a diene and one with a dienophile, react to form a six-membered ring. In this case, the diene is cyclopentadiene and the dienophile is dichloroacetyl chloride. The reaction proceeds through a concerted mechanism, with the two molecules forming a six-membered ring in a single step. The product of the reaction is a 1,4-cyclohexadiene derivative.
The following is a diagram of the Diels-Alder reaction between cyclopentadiene and dichloroacetyl chloride:
The major product of the reaction is the endo product, which is formed when the diene and dienophile react in such a way that the two double bonds in the product are on the same side of the six-membered ring. The endo product is more stable than the exo product, which is formed when the diene and dienophile react in such a way that the two double bonds in the product are on opposite sides of the six-membered ring.
The following is a diagram of the endo and exo products of the Diels-Alder reaction between cyclopentadiene and dichloroacetyl chloride:
The endo product is the major product of the reaction because it is more stable. The endo product is more stable because it has less steric strain. The exo product has more steric strain because the two bulky chlorine atoms are in close proximity to each other in the product.
The following is a diagram of the steric strain in the exo product of the Diels-Alder reaction between cyclopentadiene and dichloroacetyl chloride:
The steric strain in the exo product makes the product less stable than the endo product. The endo product is more stable because it does not have any steric strain.