Chemistry · General Principles Of Organic Chemistry · NEET
No. In position isomerism the functional group is the SAME but sits at a different carbon (propan-1-ol vs propan-2-ol - both alcohols). In functional isomerism the functional group ITSELF changes (propan-1-ol, an alcohol, vs methoxyethane, an ether). Rule: same group, different place = position; different group = functional.
Yes. Both have the general formula CnH2n+2O. For C3H8O, propan-1-ol (CH3CH2CH2OH, an alcohol) and methoxyethane (CH3OCH2CH3, an ether) have the same molecular formula but different functional groups (-OH vs -O-). This is one of the most common functional isomer pairs asked in NEET.
Both aldehydes and ketones contain the carbonyl (>C=O) group and share the formula CnH2nO. The formula C3H6O represents propanal, CH3CH2CHO (an aldehyde, -CHO), and propanone, CH3COCH3 (a ketone, >C=O in the chain). Same formula, different functional group, so they are functional isomers.
In functional isomerism the functional group changes (alcohol vs ether). In metamerism the functional group stays the same (for example both are ethers) but the alkyl groups on either side of it differ in size, like CH3-O-C3H7 vs C2H5-O-C2H5. Metamerism is really a sub-type where only the alkyl distribution changes, not the group.
Common NEET pairs: alcohols and ethers (CnH2n+2O), aldehydes and ketones (CnH2nO), carboxylic acids and esters (CnH2nO2), and cyanides and isocyanides (R-CN vs R-NC). Learning these general formulas lets you spot functional isomers quickly in the exam.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is when two compounds have the same molecular formula but different functional groups, so they belong to different families and behave differently in reactions - for example an alcohol and an ether from the same formula C3H8O.
C3H6O gives propanal (CH3CH2CHO, an aldehyde) and propanone (CH3COCH3, a ketone, also called acetone). Same formula, different functional group, so they are functional isomers.
No. Because the functional group is different, functional isomers usually have different boiling points, reactivity and chemical tests. For example an alcohol gives effervescence with sodium metal, while its ether isomer does not.
Yes. Functional group isomerism is one type of structural (constitutional) isomerism, along with chain, position and metamerism. All of these involve the same molecular formula but a different arrangement of atoms.
