What determines the boiling point of esters of the same number of carbon atoms but different structural formula?
In this case you have consider the degree of branching of the isomer, this influences the strength of intermolecular forces. Think of how tree logs with lots of branches sticking out cannot stack together with each other as easily as a pile of logs with no branches. Branched chain isomers have less contact and therefore weaker intermolecular forces and lower boiling point and straight chained isomers have better contact and thus stronger molecular forces and higher boiling point.