Mass spectra fragmentation patterns

To test this hypothesis, feeding experiments were performed with (5S)- and (5i )-[2- C, 5- Hi] mevalonate to cultures of Claviceps sp. strain SD58. Based on the mass spectra fragmentation patterns of the elymoclavine produced under these conditions the authors concluded that This experiment thus suggests that the scrambling of C from C-2 of mevalonate between C-7 and C-17 of elymoclavine and that of from C-5 of mevalonate between the two allyUc hydrogen positions of the the isoprenoid unit occur independently of each other (although not necessarily in different reaction steps). ... 

Mass spectrum fragmentation pattern of dorzolamide hydrochloride... 

Scheme 3 Mass spectrum fragmentation pattern for 1,2,4-triazine 9.

The mass spectrum fragmentation patterns of a number of 2-(4-substituted-phenyl)-l,2,3,4-tetrahydro-l,4-benzodiazepin-5-ones and their tetrazolo[l,5-rfl derivatives have been reported <94JCR(S)62>. 

Additional justification of this assignment was that the IR spectrum was identical with heridanin except for the presence of a much larger band for a hydroxy group. The mass spectrum fragmentation pattern of compound VI also resembled that of heritianin. The... 

Mass spectral fragmentation patterns are usually complex, and the molecular ion is often not the base peak. The mass spectrum of propane in Figure 12.2, for instance, shows a molecular ion at m/z = 44 that is only about 30% as high as the base peak at m/z = 29. In addition, many other fragment ions are present. 

Because mass-spectral fragmentation patterns are usually complex, it s often difficult to assign structures to fragment ions. Most hydrocarbons fragment in many ways, as the mass spectrum of hexane shown in Figure 12.4 demonstrates. The hexane spectrum shows a moderately abundant molecular ion at m/z = 86... 

Figure 8.6 Mass spectrum of C34 w-alkane (C34H70). The complete molecule appears at M = 478 and various fragment ions (m/z = 57, 71, etc.) at lower masses. The fragmentation pattern is shown on the molecular structure.

Electronic databases of the mass spectral fragmentation patterns of known molecules can be rapidly searched by computer. The pattern and intensity of fragments in the mass spectrum is characteristic of an individual compound so comparison of the experimental mass spectrum of a compound with those in a library can be used to positively identify it, if its spectrum has been recorded previously. 

Clivojuline (195) (10) represents an unusual structural type since it lacks the 9,10-aromatic oxygenation pattern, which is ubiquitious among the other lactone alkaloids. The structure of the related alkaloid cliviahaksine (196) was assigned on the basis of spectral comparisons with 195 although its stereochemistry was not specifically indicated (15). Since cliviaaline (197) was isolated in only very small amounts, its structure was deduced principally from its IR spectrum and its mass spectral fragmentation pattern however, the possibility that it was an artifact was not rigorously excluded (14). 

Mass spectral fragmentation patterns in the spectra of these compounds are in accord with the formation of alkynes. The first step in the fragmentation of 1,2,3-selenadiazoles is the loss of N2 followed by extrusion of selenium and formation of the corresponding alkyne. The abundance of the alkynic ion in the mass spectrum appears to be dependent on the nature of the substituent group present in the selenadiazole. When the alkynic ion cannot be stabilized by the formation of a cation on the adjacent carbon atoms, the abundance of the alkynic ion decreases (10% in the parent compound and zero for 4-f-butyl-l,2,3-selenadiazole). On the basis of the mass spectral pattern it is possible to predict the yield of the alkynic compound formed through pyrolysis or photolysis of a given... 

The mass spectral fragmentation pattern for (50) (70JHC639) and its X-ray crystal structure (78AX1136) have been reported. The most abundant spedes in the mass spectrum of (50) is the [yVf-56] ion which corresponds to the loss of four nitrogens. The X-ray picture of (50) indicates it is a planar molecule with a great deal of alkenic character assodated with the double bonds of the pyridazine ring. 

C-8 hydroxyl group and the C-2 of the ring B alkene. The mass spectroscopic fragmentation pattern and a careful assignment of the NMR spectrum allowed the formulation of several part structures from which the final structure was deduced. 

From the UV spectrum it became apparent that a conjugated hetero-annular diene comparable with that of buxamine-E and buxaminol-E (cf. Vol. IX, p. 405) is involved. The IR spectra showed the amide bands and the PMR spectra revealed the presence of three tertiary and one secondary C-methyl, one dimethylamino group, one primary alcohol, a proton adjacent to the secondary alcohol, and one amidic and two methylene protons. Moreover, 226 displayed signals of two methyls of the isobutyramide side chain whereas 227 showed benzamide substitution. The measured values are in accordance with the mass-spectrometric fragmentation pattern. 

The postulated primary chemical steps can be examined in the light of the mass spectroscopic fragmentation pattern of F-cyclobutane (14), which shows C2F/ as the parent peak (abundance 100 arbitrary units). A 1-3 split is also favorable C3Fr,+ has an intensity of 87 units, and CF3 25 units. These data are consistent with Steps 5b and 5c. Rupture of a C—F bond (Reaction 5a) must be more important in the radiolysis mechanism than indicated by the low abundance of 0.1 unit for the C4F7+ ion in the mass spectrum. However, this anomaly occurs not only in other fluorocarbon systems (1, 5, 10, 11, 22) but in most hydrocarbon systems studied to date. The intensities of CFL>+ and CF+ are also substantial in the mass spectrum, being 13 and 54 units respectively. These results, and the fact that CFL> has often been found under pyrolytic conditions (2,12), suggest the possibility that difluorocarbene plays a role in the mechanism, perhaps leading to a portion of the odd-carbon products. We have no evidence on this point, however. 

Characteristic fragmentation patterns are associated with specific functional groups these can help identify a substance based on its mass spectrum. The patterns were recognized after the mass spectra of many compounds containing a particular functional group were studied. We will look at the fragmentation patterns of alkyl halides, ethers, alcohols, and ketones as examples. 

HPLC-NMR and another hyphenated, more powerful instrument, HPLC-NMR-MS (the MS stands for mass spectrometry) are used in pharmaceutical research and development. These hyphenated techniques identify not only the structures of unknowns, but with the addition of MS, the molecular weight of unknown compounds. The HPLC-NMR-MS instrument separates the sample on the HPLC column, takes the NMR spectra as the separated components flow through the probe and then acquires the mass spectrum of each separated component to determine the molecular weight and additional structural information from the mass spectral fragmentation pattern. The MS must be placed after the NMR, since MS is a destructive technique. MS is covered in Chapters 9 and 10. 

The structure for pergolide mesylate (1) is supported by other spectroscopic evidence. For example, aromaticity is observable in the IR spectrum and in fragments (m/z 144, 267, 285) of the mass spectrum. The mass spectmm fragmentation pattern also supports the connectivity of the ring systems of the molecule. 

---