Constitutional (structural) isomers of esters
Constitutional (structural) isomers are compounds that have the same molecular formula but a different atom-to-atom bonding sequence. Since constitutional isomers have different physical properties, usually they can be separated easily from each other.
Constitutional isomers of esters that have the formula C5H10O2 are used below to illustrate different atom-to-atom bonding sequences.
(1)
(2)
(2)
Constitutional (structural) isomers may have the same functional group and the same carbon skeleton (The carbon skeleton shows the arrangement of carbon atoms.), but the functional group is attached to a different carbon atom.
Examples of this type are the constitutional isomers (1) and (2).
This type of constitutional isomerism is also known as positional isomerism.
This type of constitutional isomerism is also known as positional isomerism.
(3) 
(4)
(4)
Constitutional (structural) isomers may have the same functional group and different carbon skeletons.
Constitutional isomer (3) is a C5H10O2 isomer with a carbon skeleton different from that of (1) and (2).
Constitutional (structural) isomers may a different functional group.
Constitutional (structural) isomers may a different functional group.
Constitutional isomer (4) is a C5H10O2 isomer with a functional group different to that of (1) and (2).