Question

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

Answer 1

By the fragmentation pattern.

Explanation:

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.