Pyridines mass spectra

Klemm and coworkers18a prepared some isomeric chlorinated 2,3-dihydrothieno-[2,3-b]pyridine 1-oxides and reported their El mass spectra at 70 eV. Only one isomer (30) was isolated in the case of the 5-ethyl derivative the mass spectrum of which... 

Spectroscopy. In the methods discussed so far, the information obtained is essentially limited to the analysis of mass balances. In that re.spect they are blind methods, since they only yield macroscopic averaged information. It is also possible to study the spectrum of a suitable probe molecule adsorbed on a catalyst surface and to derive information on the type and nature of the surface sites from it. A good illustration is that of pyridine adsorbed on a zeolite containing both Lewis (L) and Brbnsted (B) acid sites. Figure 3.53 shows a typical IR ab.sorption spectrum of adsorbed pyridine. The spectrum exhibits four bands that can be assigned to adsorbed pyridine and pyridinium ions. Pyridine adsorbed on a Bronsted site forms a (protonated) pyridium ion whereas adsorption on a Lewis site only leads to the formation of a co-ordination complex. 

Examination of the mass spectrum of P2VPY taken during the maximum decomposition rate reveals the major decomposition products as methylpyridine (93 a.m.u.), protonated vinyl pyridine (106 a.m.u.), and protonated dimer (211 a.m.u.) with ion ratios 74 100 59 respectively. Trimeric and tetrameric protonated species (316 and 421 a.m.u.) are also observed but in relatively small amounts. Protonated ions, rather than the simple monomers and dimers observed for the decomposition of poly(styrene) by MS11, may be created by a mechanism similar to that reported for the decomposition of 2-(4-heptyl)pyridine12 in the mass spectrometer. 

Fig. 6.53. El mass spectrum of pyridine. HCN loss represents the most important primary fragmentation of the molecular ion. Spectrum used by permission of NIST. NIST 2002.

The mass spectrum of aniline has been known since the early days of mass spectrometry. [122] Initially, the observed [M-27] ion has been interpreted in terms of HCN loss (Fig. 6.56a). The mechanism for loss of the elements of [H, N, C] from aminoarenes is perfectly analogous to CO loss from phenols (Chap. 6.9.1). [231] More recently, it could be demonstrated that loss of hydrogen isocyanide, HNC, occurs rather than losing the more stable neutral species HCN, a behavior typical of ionized pyridine. [222]... 

Two isomeric complexes, 60 and 61, have been analyzed by Cl MS (reagent gas CH4), producing [M -b I] and [M -b 29]+ ions. Electron ionization mass spectrometry was applied in the analysis of the product of the reaction between Zn(CF3)Br-2CH3CN (62) and 4-(Af,Af-dimethylamino)pyridine (DMAP). The El (20 eV) mass spectrum of the product, Zn(CF3)Br DMAP (63), was recorded at 280 °C and consisted mainly of [C6H3BrF2NZn]+, [ZnBr2]+ and [ZnBr]+ ions. At lower temperatures, this compound did not yield any Zn-containing ions, and the spectra were dominated by the peaks of the [DMAPJ+ and [C2HgN]+ ions . 

Beynon et al. have reported that the energy release during the decomposition of metastable peaks in the mass spectrum of 1,3,5-triazine was 187 peV, a lower value than for either pyridine or pyrimidine <710MS(5)229>. 

Dehydroguattescine (117) was found in G. schomburgkiana (50,51). Its spectral properties showed that it resembled guattescine (116) quite closely. Its mass spectrum, however, indicated a molecular weight lower than that of guattescine by 2, and the H-NMR spectrum exhibited a typical pyridine AB system at 7.44 and 8.38 ppm (7 = 6 Hz). These data led to the proposal of structure 117, which received support from its semisynthetic preparation by m-chloroperbenzoic acid oxidation of O-methylbelemine (147) (see below). Dehydroguattescine is the only 7-hydroxy-7-methyl-4,5,6,6a-tetradehydroaporphine known so far. 

An interesting class of elusive neutral species is heterocyclic ylids, as represented by the so-called Hammick intermediate that was postulated 65 years ago to explain the accelerated decarboxylation of 2-picolinic acid [146, 147]. An analogous dissociation takes place in ionized 2-picolinic acid in the gas-phase and was employed to generate the pyridine ion isomer 35+ (Scheme 13) [148]. Collisional neutralization of 35+ with A/,AT-dimethylaniline produced neutral ylid 35, which can also be represented as a singlet a-carbene (Scheme 13). Ylid 35 showed a survivor ion in the +NR+ mass spectrum, which was further char-... 

The molecular weight of evonine,68 composed of a base and a polyhydroxy moiety of still unknown structure, could not be determined by mass spectrometry, because the alcohol component was too easily eliminated. Nevertheless, important parts of the structure of the base can be deduced from the mass spectrum of the LiAlH4-reduction product of evonine (137) which exhibits a significant peak at mass 137, indicating the presence of a substituted pyridine of type [138], (137)—>[138]— -[139] ... 

Figure 6.2.12. Mass spectrum assigned to 2-(3-phenylbut-3-enyl)pyridine.

Reduction (LiAlH4) of the pachystermines-A and -B gives the pachystermine-diol (232), which was methylated to (233). Treatment of (232) with methane-sulphonyl chloride in pyridine gives the azetidine (234), characterised by an intense peak at m/e 138 in its mass spectrum. Under the same conditions, (233)... 

---