Here's why:

* Stearate refers to the stearic acid molecule, which has a long hydrocarbon chain with a carboxylic acid group (-COOH) at one end.

* Methyl indicates the presence of a methyl group (-CH3) attached to the molecule.

* Ester is formed when a carboxylic acid reacts with an alcohol, with the removal of water. In this case, the carboxylic acid group of stearic acid reacts with the alcohol group of methanol (CH3OH), forming the ester linkage (-COO-) between the stearate and methyl groups.

Therefore, methyl stearate has the following structure:

CH3(CH2)16COO-CH3

The -COO- group is the ester functional group.