Mass Spectrometry of Some Common Functional Groups

Mass Spectrometry of Some Common Functional Groups 

As each functional group is discussed in future chapters, mass-spectral fragmentations characteristic of that group will be described. As a preview, though, we ll point out some distinguishing features of several common functional groups. 

Alcohols undergo fragmentation in the mass spectrometer by two pathways alpha dcava ic and dehydration. In the a-cleavage pathway, a C-C bond nearest the hydroxyl group is broken, yielding a neutral radical plus a resonance-stabilized, oxygen-containing cation. 

In the dehydration pathw ay, water is eliminated, yielding an alkene radical cation with a mass 18 units less than 

Aliphatic amines undergo a characteristic a cleavage in the mass spectrometer, similar to that observed for alcohols. A C—C bond nearest the nitrogen atom is broken, yielding an alkyl radical and a resonance-stabilized, nitrogen-containing cation. 

In addition, ketones and aldehydes frequently undergo a cleavage of the bond between the carbonyl group and the neighboring carbon. Alpha cleavage yields a neutral radical and a resonance-stabilized acyl cation. 

416 CHAPTER 12 Structure Determination Mass Spectrometry and Infrared Spectroscopy 

The male sex hormone testosterone contains only C, H, and O and has a mass of 288.2089 amu, as determined by high-resolution mass spectrometry. What is the likely molecular formula of testosterone  

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Mass Spectrometry of Some Common Functional Groups 415... 

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