Mass spectrum, of 2-butanone

The mass spectrum of 2-butanone. Note the prominent molecular ion, together with a base peak from loss of an ethyl radical to give an acylium ion. 

Using Figures 14.7 and 14.8 as a model, predict the fragmentation and mass spectrum of 2-butanone. 

Ketones undergo a reduction when treated with sodium borohydride, NaBH What is the structure of the compound produced by reaction of 2-butanone with NaBH4 if it has an IR absorption at 3400 cm-1 and M+ = 74 in the mass spectrum ... 

Example In the El mass spectrum of 3,3-dimethyl-2-butanone no fragment ion due to McLafferty rearrangement can be observed, because there is no y-hydrogen available (Fig. 6.23). Instead, the products are exclusively formed by simple cleavages as evident from their odd-numbered m/z values. The highly stable tert-butyl ion, m/z 57, predominates over the acylium ion at m/z 43 (Chap. 6.6.2). 

Treatment of 2-butanone (CHsCOCH2CH3) with strong base followed by CH3I forms a compound W, which gives a molecular ion in its mass spectrum at 86. The IR (> 1500 cm only) and NMR spectrum of W are given below. What is the structure of W ... 

Figure 18-3 shows the mass spectrum of methyl ethyl ketone (2-butanone). The molecular ion is prominent at m/z 72. The base peak at m/z 43 corresponds to loss of the ethyl group. Because a methyl radical is less stable than an ethyl radical, the peak corresponding to loss of the methyl group ( w/z 57) is much weaker than the base peak from loss of the ethyl group. 

The parent ion of 2-butanone has m/z = 72 and it can fragment on both sides of the carbonyl. One cleavage leads to daughter ions m/z = 43 and m/z = 29. Cleavage on the other side of the carbonyl leads to daughter ions m/z = 15 and m/z = 57. All five of these ions are drawn on the simulated mass spectrum. 

The results of the interpretation of the gas phase IR and low-resolution mass spectra of 4-phenyl-2-butanone are given in Figure 4. This compound, with a molecular weight of 148, is t3rpical of the size and complexity of compounds which our program handles well. The IR spectrum was taken from the EPA gas-phase IR library, and the mass spectrum from the Registry of Mass Spectral Data.(35)... 

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