DF 9 notes 

==Isomerism === molecules that have the sake molecular formulae but differ in the way their atoms are arranged. They are distinct compounds with different physical and often different chemical properties,

==Structural isomers== – the atoms are bonded together in a different order

==Stereoisomers== – the order of bonding is the same but the arrangement of the atoms in the space is different

==Chain isomerism== – with 4 or more carbon atoms in a chain, different arrangements are possible

==Positional isomerism== – occurs when a functional group is situated on different positions in the molecules

==Functional group isomerism== – compounds with the same molecular formular that have different functional groups. Therefore belong to a different homologous series

==Stereoisomer== – E/Z isomerism can be used when the two groups that are the same are H

-       Cis/trans isomerism can be used when the 2 groups that are the same are not H