Chemistry · Alcohols, Phenols And Ethers · NEET
Metamerism is a type of structural isomerism. Two compounds are metamers when they have the same molecular formula AND the same functional group, but the alkyl groups attached on the two sides of the functional group are different. Think of the functional group (the ether oxygen) as fixed in the middle, and the carbon chain being split between the left arm and the right arm in different ways. Diethyl ether splits 4 carbons as 2+2. Methyl propyl ether splits the same 4 carbons as 1+3. Same formula C4H10O, same ether group, different arms - so they are metamers.
An ether can show metamerism only if its total carbons can be split around the oxygen in more than one way. C2H6O (only CH3-O-CH3) cannot - one carbon on each side is the only option. C3H8O ether is only CH3-O-CH2CH3 (methyl ethyl) - splitting 3 carbons as 1+2 gives just one ether, so no metamer. C4H10O is the FIRST ether to show metamerism: you can split 4 carbons as 2+2 (diethyl ether) or 1+3 (methyl propyl ether). So the minimum is 4 carbons in the ether.
Both are structural isomerism, but they change different things. In chain isomerism the carbon skeleton itself branches differently (like n-pentane vs isopentane) and there may be no functional group at all. In metamerism the functional group is present and stays the same; only the way the alkyl groups are distributed around that functional group changes. Key clue for NEET: metamerism needs a divalent functional group in the middle (like -O- in ethers, -CO- in ketones, or the N in amines). Alkanes cannot show metamerism because they have no such functional group.
For an ether R-O-R', both R and R' must have at least one carbon. C3H8O as an ether means 3 carbons split around the O. The only split is 1+2, giving CH3-O-CH2CH3 (methyl ethyl ether). There is no second way to split 3 carbons into two non-zero pieces (a 0+3 split is not an ether, it is an alcohol). C4H10O splits 4 carbons two ways: 2+2 (diethyl ether) and 1+3 (methyl n-propyl ether), so it has metamers. Note: C3H8O still has isomers overall (propan-1-ol, propan-2-ol, methyl ethyl ether), but those are functional/positional isomers, NOT metamers.
No. Any compound with a divalent functional group sitting between two alkyl groups can show metamerism. Ethers (R-O-R') are the most common NEET example. Ketones (R-CO-R'), secondary and tertiary amines (R-NH-R'), and esters can also show it. In NEET, this concept is almost always tested using ethers, so learn the ether case first - especially that C4H10O is the smallest ether that shows metamerism.
The compound which shows metamerism is:
The pair of molecules that are metamers among the following is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Four. C4H10O is the smallest ether that shows metamerism, existing as diethyl ether (2+2 split) and methyl n-propyl ether (1+3 split). Ethers with 2 or 3 carbons have only one possible structure each, so they have no metamer.
Metamerism is a type of structural (constitutional) isomerism. The atoms are connected in a different order around the functional group. It is not stereoisomerism, where the connectivity is the same but the 3D arrangement differs.
Yes. Both have the molecular formula C4H10O and both are ethers, but diethyl ether splits the carbons as ethyl+ethyl (2+2) while methyl propyl ether splits them as methyl+propyl (1+3). Different alkyl groups around the same -O- makes them metamers.
No. Metamerism needs a divalent functional group between two alkyl groups (like -O- in ethers). An alcohol has -OH at the end of a chain, not between two groups, so alcohols show chain, positional, or functional isomerism instead, but not metamerism.
