2-Methyl-2-butanol mass spectrum

Three of the most intense peaks in the mass spectrum of ] 2 methyl 2 butanol appear at m/z 59 70 and 73 Explain the origin of these peaks J... 

The mass spectra of alcohols often completely lack a peak corresponding to the parent ion. This is due to extremely rapid loss of neutral fragments following initial ionization. For example, the mass spectrum of 2-methyl-2-butanol lacks a parent peak and contains strong peaks at M-15 (loss of CH3O and M-18 (loss of H2O). 

The molecular weight of 2-methyl-2-butanol is 88. A peak in its mass spectrum at m/z 70 corresponds to loss of water from the molecular ion. The peaks at m/z 73 and m/z 59 represent stable cations corresponding to the cleavages shown in the equation. 

Sanchez and Brown have obtained a new harman derivative from Aspi-dosperma exalatum Monachino (121). The alkaloid was obtained from a butanol extract, and in the IR spectrum it showed principal absorptions at 1925 cm-1 for an immonium ion, at 1610 cm-1 for a carboxylate anion, and at 748 cm-1 for a disubstituted benzene. In the mass spectrum a molecular ion was observed at m/e 226 and a base peak at m/e 182 (M+ —44). An aromatic methyl group and five aromatic protons were observed in the PMR spectrum. Consideration of this data together with the UV spectrum led to deduction of the structure of the alkaloid as 268, harman carboxylic acid. The ethyl ester (269) was also isolated but it was probably an artifact. 

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 ... 

The mass spectrum of 3-methyl-l-butanol (Figure 12-21) shows a favorable loss of water. The peak at m/z 70 that appears to be the molecular ion is actually the intense M-18 peak. The molecular ion m/z 88) is not observed because it loses water very readily. The base peak at m/z 55 corresponds to loss of water and a methyl group. 

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 identification of the photodegradation products of fexofenadine obtained in UV was performed based on molecular ions [M4-H]+. The mass spectrum of DP-1 show the molecular ion at m/z = 457 amu, and the product was identified as the 4-[4-(hydroxydiphenyl-methyl)-l-piperidinyl]-l-(4-phenylisopropyl)butanol. The second product DP-2 (m/z = 499 amu) was identified as a,a,-dimethyl-4-[l-hydroxy-4-[4-(benzophenone)l-piperidinyl]buthyl]-benzene acetic acid. 

A low-resolution mass spectrum of 2-methyl-2-butanol (MW 88) shows 16 peaks. The molecular ion is absent. Account for the formation of peaks at mtz 73, 70,59, and 55 and propose a structural formula for each cation. 

Following is the mass spectrum of 3-methyl-2-butanol. The molecular ion m/z 88 does not appear in this spectrum. Propose structural formulas for the cations of m/z 45,43, and 41. 

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... 

Carbocations can also be stabilized by a heteroatom that bears a lone pair of electrons able to donate into the empty p orbital (Figure 5.24). Thus, in mass spectrometry, the fragmentation generally occurs such that the cation formed can be stabilized by the heteroatom. The mass spectrum of 2-methyl-2-butanol (Figure 5.25) illustrates. The molecular ion (M would be 88) is not seen as there are good routes to stable cations. The peaks at m/z 73 and 59 represent the loss of methyl and ethyl radicals to give cations stabilized by lone pair... 

Following are mass spectra for the constitutional isomers 2-pentanol and 2-methyl-2-butanol. Assign each isomer its correct spectrum. 

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