Mass Spectroscopy, Example #5

Analysis: C5H8O2 MW = 100.12 Help with Analysis
Mass Spectrum

Mass Spectrum

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C5H8O2 MW = 100.12

From the molecular formula, the compound has "2 degrees of unsaturation" (two double bonds, carbonyls or rings).

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The spectrum shows a small molecular ion peak, and a pair of peaks at m/e = 57 and 58. The peak at m/e = 57 corresponds to loss of m/e = 43, which is the base peak and corresponds to the acylium ion (CH3CO+). The m/e = 57 fragment corresponds to C3H5O, suggesting the original compound was an ester with this molecular formula.

Fragmentation of Common Functional Groups
Common Ions and Fragments

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Structure: structure

IUPAC Name: 2-propenyl ethanoate (allyl acetate)

MS Fragments:
fragments

The spectrum shows a small molecular ion peak, and a pair of peaks at m/e = 57 and 58. The peak at m/e = 57 corresponds to loss of m/e = 43, which is the base peak and corresponds to the acylium ion (CH3CO+). The m/e = 57 fragment corresponds to C3H5O, suggesting the original compound was an allyl (-O-CH2CHCH) or methylvinyl (-O-CHCHCH3) ester. Either of these would generate the peak observed at m/e = 41. The peak at m/e = 58 corresponds to the protonated m/e = 57 cation radical. Proton or 13 C NMR would readily distinguish between the two possibile structures.

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Copyright 1996, Paul R. Young, University of Illinois at Chicago, All Rights Reserved