exitst when molecules are composed of the same number & type of atoms but these atoms are arranged in different ways.
the atoms making up the isomers are joined up in the same order but have different arrangement in space.
The C skeletal can be rearranged differently, either as a straight chain or as a branched chain in different ways.
These ismoers ahve similar chemical properties but different physical properties because of the change in shape of the molecule.
The skeleton & functional gropu can be the same, but the group could be attached to a different carbon atom.
This leads to different chemical & physical properties.
Functional Group Isomers
The same atoms can be arranged into different functional groups, this leads to a difference in chemical properties.
There must be a C=C (double bond) and each carbon must be attached to 2 different groups.