How would #"mass spectroscopy"# differentiate between #"2-pentanone"# and #"3-pentanone"#?

1 Answer
Feb 4, 2016


By the fragmentation pattern.


As you know, the molecular ions of both 2-pentanone and 3-pentanone have identical mass. They would not have the same fragmentation pattern. How would you know which is which? Run a mass spectrum of authentic 2-pentanone under given conditions, and then authentic 3-pentanone under identical conditions. The two ketones would exhibit different fragmentation patterns in their mass spectra, and should be distinguishable even though they give identical molecular ions.

A much better means of analysis would be by #""^1H# #NMR# spectroscopy; here, the spectra could be easily differentiated.