Here's why:

* Isopentyl acetate is an organic compound with the formula CH₃COOCH₂CH₂CH(CH₃)₂.

* Esters are formed by the reaction of a carboxylic acid and an alcohol. They have the general structure R-COOR', where R and R' are alkyl or aryl groups.

In the case of isopentyl acetate:

* R-CO corresponds to the acetyl group (CH₃CO-) from acetic acid.

* OR' corresponds to the isopentyl group (CH₂CH₂CH(CH₃)₂) from isopentyl alcohol.

Therefore, the presence of the -COOR' group in isopentyl acetate makes it an ester.