Butyraldehyde mass spectrum

These model studies permitted demonstration of metabolic a-hydroxylation of NPy by isolating 2-hydroxytetrahydrofuran as a metabolite of NPy. This was accoitplished by trapping 4-hydroxy-butyraldehyde as its 2,4-dinitrophenylhydrazone (DNP) derivative. For in vitvo studies, NPy-2,5-l C was incubated with rat liver microsomes, 02i and an NADPH generating system. After the incubation was complete, DNP reagent was added to the mixture and the products were extracted and examined by preparative TLC. A radioactive band corresponding to the DNP of 4-hydroxybutyralde-hyde was observed. This band was not present in controls in which NADPH was omitted or in which boiled enzyme was used. The mass spectrum was identical to that of a reference sairple. In addition, a minor metabolite with mass spectrum identical to that of the DNP of 2-butenal was also isolated. These results showed conclusively that NPy underwent metabolic a-hydroxylation in this in vitro system. 

McLafferty Rearrangement of Ketones and Aldehydes The mass spectrum of butyraldehyde (Figure 18-4) shows the peaks we expect at m/z 72 (molecular ion), m/z 57 (loss of a methyl group), and m/z 29 (loss of a propyl group). The peak at m/z 57 is from cleavage between the /3 and y carbons to give a resonance-stabilized carbocation. This is also a common fragmentation with carbonyl compounds like the other odd-numbered peaks, it results from loss of a radical. 

The mass spectrum of butyraldehyde shows the expected ions of masses 72, 57, and 29. The base peak at m/z 44 results from the loss of ethylene via McLafferty rearrangement. 

The peak due to the loss of one hydrogen atom is very characteristic of aldehydes. This peak is observed at m/e = 71 in the mass spectrum of butyraldehyde (Fig. 8.28). Thepeakdue to the formation of HCO" can be observed at mle = 29 this is also a very characteristic peak in the mass spectra of aldehydes. 

Coincidentally, the fragment ion also occurs at m/e = 29 in the mass spectrum of butyraldehyde. However, in higher aldehydes it occurs at higher m/e values. At any rate, the mass of this peak is 43 mass units less than that of the molecular ion. 

The fragment ion formed in this rearrangement has m/e = 44. A peak at m/e = 44 is considered to be quite characteristic of the mass spectra of aldehydes. It is the most intense peak in the mass spectrum of butyraldehyde. Note that this rearrangement occurs only if the chain attached to the carbonyl group has three or more carbons. 

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