Answer
The Diels–Alder reaction predominantly produces ring-shaped compounds due to its cycloaddition mechanism. In this reaction, a conjugated diene and a dienophile undergo a concerted cycloaddition, resulting in the formation of a six-membered cyclic structure. This reaction is highly versatile and widely employed in organic synthesis for the construction of various cyclic systems, including cyclohexenes, cyclopentenes, and more complex polycyclic structures.