Heptanones, mass spectra

Figure 10.24 A mass spectrum of an aliphatic ketone, 3-heptanone, C7H14O.

FIGURE 2.64 Mass spectrum of 3-heptanone ethylene ketal. 

If an unknown compound were converted to an ethylene ketal and its mass spectrum recorded as that in Figure 2.64, structure elucidation would not be difficult. Subtracting 72 Da (the mass of the known portion of the molecule) from each of the two intense fragment ion peaks at miz 101 and 129 leaves 29 and 57 Da, respectively. R and R in this molecule are then ethyl and butyl, and the compound is the ethylene ketal of 3-heptanone (Equation 2.94). 

PROBLEM 12.18 In what ways will the mass spectrum of 4-heptanone be similar to and in what ways will it differ from the mass spectrum in Figure 12.11 ... 

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