Are ethyl butanoate (1) and propyl propanoate (2) metamers or functional group isomers? My book claims they are metamers, but here one group is $\ce{-CO-OR}$ and another is $\ce{-CO-OR'}$ where $\ce{R}$ is $2$ carbon and $\ce{R'}$ is $3$ carbon. Though both of them are esters, aren't the functional groups different?

1: ethyl butanoate; 2: propyl propanoate


1 Answer 1


Metamerism occurs when isomers have different alkyl chains on the sides of the functional groups. In the case of an ester, the relevant functional group is the ester (..O-C=O..) group. The length of R and R' has no bearing on the functional group in this case. An example of a functional isomer would be something like ethyl butanoate and caproic acid.


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