Question:Draw the product formed in each cycloaddition.

In a [2+2] cycloaddition reaction, 2 alkene systems react to form a 4-membered ring system. The reaction occurs under photochemical conditions.

In the case of a [2+2] cycloaddition, the bond formation occurs antarafacially since only one set of terminal carbons have the like phases facing each other. For the bond formation to occur, the molecules need to be twisted.

For this reason, photochemical conditions are required since light energy transfers an electro to the excited HOMO orbital. The overlap is shown below:

a. The reactants are redrawn, and the product is shown below:

[2+2] cycloaddition of compound a

b. The reactants are redrawn, and the product is shown below:

[2+2] cycloaddition of compound b