Differentiation of isomeric structures

Unlike NMR spectroscopy, mass spectrometry is poorly disposed in its ability to differentiate isomeric compounds. Several examples are, however, known that demonstrate the ability of mass spectrometry in unambiguous identification of isomers. Some representative examples are discussed here  

Similarly, isomeric primary, secondary, and tertiary amines are differentiated on the basis of their distinct a-cleavage products. 

As shown in Fignre 6.10, the radical cations of 3-pentanone and 3-methyl-2-butanone yield distinct a-cleavage products  

The former produces miz 57 (C2H5CO+), whereas the latter yields m/z 43 (CH3CO+). 

The McLafferty rearrangement can also provide isomer-specific data. For example, this rearrangement is able to distinguish 4-methyl-2-pentanone 

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Information about the monomeric composition and structure can be obtained with pyrolysis MS but sequence information is lost [46]. The method was used in several applications, such as structural identification of homopolymers, differentiation of isomeric structures, copolymer composition and sequential analysis, identification of oligomers formed in the polymerization reactions, and identification of volatile additives contained in polymer samples [47]. One of the main challenges of the technique is the identification of the products in the spectrum of the multicomponent mixture produced by thermal degradation. 

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