Editing Structural isomer (section)

==Functional isomerism==
'''Functional isomers''' are structural isomers which have different [[functional group]]s, resulting in significantly different chemical and physical properties.<ref name=hinw1997/>

An example is the pair [[propanal]] H<sub>3</sub>C–CH<sub>2</sub>–C(=O)-H and [[acetone]] H<sub>3</sub>C–C(=O)–CH<sub>3</sub>: the first has a –C(=O)H functional group, which makes it an [[aldehyde]], whereas the second has a C–C(=O)–C group, that makes it a [[ketone]].

Another example is the pair [[ethanol]] H<sub>3</sub>C–CH<sub>2</sub>–OH (an [[alcohol (chemistry)|alcohol]]) and [[dimethyl ether]] H<sub>3</sub>C–O–CH<sub>2</sub>H (an [[ether]]). In contrast, [[1-propanol]] and [[2-propanol]] are structural isomers, but  not functional isomers, since they have the same significant functional group (the [[hydroxyl]] –OH) and are both alcohols.

Besides the different chemistry, functional isomers typically have very different [[infrared spectroscopy|infrared spectra]].  The infrared spectrum is largely determined by the vibration modes of the molecule, and functional groups like hydroxyl and esters have very different vibration modes. Thus 1-propanol and 2-propanol have relatively similar infrared spectra because of the hydroxyl group, which are fairly different from that of methyl ethyl ether.{{citation needed|date=August 2020}}