A polar molecule is a molecule that has a net dipole moment due to its having unsymmetrical polar bonds. There are two factors that go into determining if a molecule is polar or not. To determine if a molecule (or ion) is polar or non-polar, you must determine both factors.
The polarity of the individual bonds in the molecule. The shape or geometry of the molecule.
First, to determine if a given individual bond is polar, you need to know the electronegativity of the two atoms involved in that bond. To find the electronegativities of all the elements, look at the periodic table (follow the link below this answer under Web Links).If the electronegativity of the two atoms has a difference of 0.3 or less, then the bond is non-polar. If the electronegativity difference is greater that 0.3 but less than 1.7, then the bond is polar. If the two values have a difference greater than 1.7, then the bond is ionic, which is just very very polar.Once you know which bonds in the molecule are polar and which are non-polar, you must use the shape of the molecule. You need the shape because two polar bonds, if oriented correctly can cancel each other out.
Methyl Oleate is ester of stearic acid and its non polarbecause stearic acid is composed of 18 carbon and the unique polar function which is COOH is esterified with the methyl.