Chain, nuclear or skeleton isomerism:
This form of isomerism arises because of the difference in the nature of the carbon chain (that is straight or branched) which makes the nucleus of the molecule.
1. Except alkynes chain isomerism is seem while the number of carbon atoms is four or much more than four.
2. Chain isomers are different in the nature of carbon chain that is in the size of carbon chain.
3. The isomers depicting chain isomerism belong to the same homologous sequence that is functional set; class of the element remains unchanged.
4. Chain and position isomerism can't be possible together among two isomeric compounds. If two compounds are chain isomers as compared to these two will not be positional isomers.