Group-0 cations hydrogen

In these examples, it can be seen that the carbon and chlorine atoms can achieve octets of electrons by sharing pairs of electrons with other atoms. Hydrogen atoms attain duets of electrons because the first shell is complete when it contains two electrons. We note from Sec. 5.4 that main group cations generally lose all their valence electrons, and then have none left in their valence shell. 

In entry 15 of Table 21.10, it is noted that even a remote hydroxyl group directed hydrogenation by the cationic [Rh(diphos-4)(nbd)]+ catalyst to afford a moderate diastereoselectivity (80 20) [23]. This is an interesting example of long-range 1,5-asymmetric induction. 

The FAB plasma provides conditions that allow to ionize molecules by either loss or addition of an electron to form positive molecular ions, M" , [52,89] or negative molecular ions, M, respectively. Alternatively, protonation or deprotonation may result in [Mh-H]" or [M-H] quasimolecular ions. Their occurrence is determined by the respective basicity or acidity of analyte and matrix. Cationization, preferably with alkali metal ions, is also frequently observed. Often, [Mh-H]" ions are accompanied by [MH-Na]" and [Mh-K]" ions as already noted with FD-MS (Chap. 8.5.7). Furthermore, it is not unusual to observe and [Mh-H]" ions in the same FAB spectmm. [52] In case of simple aromatic amines, for example, the peak intensity ratio M 7[Mh-H] increases as the ionization energy of the substrate decreases, whereas 4-substituted benzophenones show preferential formation of [Mh-H]" ions, regardless of the nature of the substituents. [90] It can be assumed that protonation is initiated when the benzophenone carbonyl groups form hydrogen bonds with the matrix. 

Section 1.3.2.A). The loose proton of the methyl group in cation radicals is capable of forming an intramolecular hydrogen bond with the oxygen atom of the ortho-hydroxy group. This hydrogen bonding keeps the proton within the fused cycle, blocks the formation of the or-tho-hydroxybenzyl radical, and retards or prevents the consequent oxidation. 

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