Gaseous cation chemistry and chain‐length effects in electron ionization and collision‐induced dissociation mass spectraof symmetric 1,n‐bis(9‐anthracenyl)alkanes

Abstract

The behavior of the gaseous cations resulting from EI (30 and 70 eV) of the bichromophoric title compounds 1-5 (for n = 1-5, respectively) is examined by ion-trap mass spectrometry, including collision-induced dissociation (CID) with variation in collision energy. These results are compared with those from anthracene and 9-methylanthracene and with previously reported mass spectrometric results for 3 and dicarbazolylalkanes. Rather than using the kinetic method to obtain ion energetics where the fragmentation mechanism is clear, as commonly done, the method is used here with relative complementary-ion abundances from CID to test the proposed fragmentation mechanisms using B3LYP calculations of relative ionization energies and optimized geometries of ionic and neutral fragments. Hydrogen migrations are common, and skeletal rearrangements including formation of expanded, fused and spiro rings are proposed in several cases. Of the chain cleavages, α-homolysis giving C(15) H(11) (+) , likely as dibenzotropylium, is most important for each of 1-5 except 3, where β-cleavage to C(16) H(13) (+) dominates with a proposed methyldibenzotropylium structure. α-Cleavage was important also in the dicarbazolylalkanes. A previous inference of a McLafferty rearrangement to explain C(15) H(12) (+•) from 3 is not supported by the present results. The fragmentation behavior of 1-5 depends strongly on n and implies significant interchromophoric interaction between anthracenyl groups.

Novel Pyrano and Vinylphenol Adducts of Deoxyanthocyanidins in Sorghum Sourdough

“…Fragments generated with Q-TRAP 4000 were used to explain the structures of the symmetric pyrano-3-deoxyanthocyanidins, typified by compound 13. 31 The conjugate π system ordinarily provides a challenge for the structure elucidation of pyrano-3deoxyanthocyanidins by MS/MS experimentation, 32 but by using pyranoapigeninidin 4-vinylphenol (compound 13) as a reference, the structures of the remaining pyrano-3-deoxyanthocyanidins can be deduced. As in compounds 6 and 8, comparison between mass spectra in deuterated and protic media was used to determine the number of phenolic hydrogens in compounds 10, 14, 15, and 20 (Figure 3 and Table 4).…”

Fragmentation of oxime and silyl oxime ether odd‐electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

“… The study of the major MS fragmentations of these carbonyl derivatives, however, has not received due attention. For example, although the McLafferty rearrangement of carbonyl compounds has been the focus of extensive and continuous research , studies on oximes and silyl oxime ethers have been limited. Surprisingly, to date, only one article has reported the McLafferty rearrangement for ketoximes.…”