Chemistry · General Principles Of Organic Chemistry · NEET
| What changes | Carbon skeleton (straight vs branched) | Position of group/bond on same skeleton |
| Molecular formula | Same | Same |
| Functional group | Same | Same |
| Example (C5H12 / C3H7OH) | pentane, isopentane, neopentane | propan-1-ol vs propan-2-ol |
No. Structural isomerism is the big family. Chain isomerism is only ONE type inside it. Other types are position, functional and metamerism. So every chain isomer is a structural isomer, but not every structural isomer is a chain isomer. In chain isomerism only the carbon skeleton (chain shape) changes.
In chain isomerism the CARBON SKELETON changes (straight chain becomes branched). In position isomerism the skeleton stays the same but the position of a substituent, double bond, or functional group moves along the chain. Rule of thumb: chain = skeleton changes; position = only the location on the same skeleton changes.
C5H12 has three chain isomers, as given in NCERT: n-pentane (straight chain), isopentane which is 2-methylbutane, and neopentane which is 2,2-dimethylpropane. All three have the same formula C5H12 but different carbon skeletons.
Yes. Pentane is CH3CH2CH2CH2CH3 (a straight five-carbon chain) and neopentane is C(CH3)4, that is a central carbon with four methyl groups (a highly branched skeleton). Same formula C5H12, different skeleton, so they are chain isomers.
No. In chain isomerism the functional group stays the same. Only the arrangement of carbon atoms in the chain changes. If the functional group itself changes (for example alcohol vs ether), that is functional isomerism, not chain isomerism.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is when compounds have the same molecular formula but their carbon atoms are joined in a different chain shape, such as a straight chain versus a branched chain.
Butane, C4H10. It has two chain isomers: n-butane (straight chain) and isobutane, which is 2-methylpropane (branched).
NEET often asks you to count isomers or to tell isomer types apart. Knowing that chain isomerism only changes the skeleton helps you separate it quickly from position and functional isomerism and avoid over-counting.
Yes, slightly. More branching lowers the boiling point because branched molecules pack less closely, so neopentane boils lower than n-pentane even though both are C5H12.
