2-Methyl-2-propanol mass spectrum

The mass spectrum of 1-butanol (Fig. 8.21) shows a very weak molecular ion peak at mie = lA, while the mass spectrum of 2-butanol (Fig. 8.22) has a molecular ion peak (rnie = 74) that is too weak to be detected. The molecular ion peak for tertiary alcohol, 2-methyl-2-propanol (Fig. 8.23), is entirely absent. The most important fragmentation reaction for alcohols is the loss of an alkyl group ... 

Figure 10.22 A mass spectrum of a tertiary alcohol, 2-methyl-2-propanol, C4H10O.

In some cases, components in a mixture can be determined quantitatively without prior separation if the mass spectrum of each component is sufficiently different from the others. Suppose that a sample is known to contain only the butanol isomers listed in Table 10.17. It can be seen from Table 10.17 that the peak at miz = 33 is derived from butanol, but not from the other two isomers. A measurement of the miz = 33 peak intensity compared to butanol standards of known concentration would therefore provide a basis for measuring the butanol content of the mixture. Also, we can see that the abundances of the peaks at m z = 45, 56, and 59 vary greatly among the isomers. Three simultaneous equations with three unknowns can be obtained by measuring the actual abundances of these three peaks in the sample and applying the ratio of the abundances from pure compounds. The three unknown values are the percentages of butanol, 2-butanol, and 2-methyl-2-propanol in the mixture. The three equations can be solved and the composition of the sample determined. Computer programs can be written to process the data from multicomponent systems, make all necessary corrections, and calculate the results. 

The library search will possibly only lead to a correct identification if the spectrum of the unknown is actually present in the library and the GC separation has been sufficiently efficient to obtain a sufficiently clean mass spectrum. When the unknown is not present in the library, the search procedure also yields valuable information in pointing out certain structural elements present in the unknown as well as structural similarities with known compounds. However, this information is only useful in combination with a proper interpretation of the mass spectrum. A fast check of the mass spectra found by the search routine against the supposed structure is advisable as well, in order to eliminate possible errors in the library. The Wiley Library, for example, contains almost identical mass spectra for 2-butanol and 2-methyl-1-propanol, while theoretically and practically, these mass spectra are distinctly different. It must also be taken into account that the vast majority of the spectra available in the library are of compounds having molecular masses between 150 and 300 Da. The number of spectra of compounds with molecular masses above 400 Da is limited, although the number... 

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