Electron Removal from Neutral Species

Generation of cations by electron removal from neutral species is certainly more of theoretical than of practical interest. 

Loss of one electron from a vinyl radical to give a vinyl cation can be achieved in the mass spectrometer (eq. 29). The minimum energy 

Electron removal from vinyl compounds, accompanied by rupture of the C-X bond, may also occur in the mass spectrometer and a vinyl cation may be generated (equation 30). 

The appearance potential of the vinyl cation from vinyl chloride is 12-81 eV. Such a value is ca. 14 kcal mol-1 higher than that of the ethyl cation from ethyl chloride (Maccoll, 1962). 

Vinyl cations and radical cations can be generated from the corresponding alkenes (equation 30). The appearance potentials and fates of the species thus generated are more of interest in mass spectrometry than in carbonium ion chemistry, and have recently been reviewed by Loudon and Maccoll (1970). 

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It has been estimated that the electron molecule interaction occurs in a very short time ( 10 16 s) and its product is the ejection of one electron from the molecule according to Equation. (2.1). The ions so formed constitute the molecular ion (M+ ). It is produced directly from the molecule but it is a positive ion. In fact, an electron has a negative charge and its removal from a neutral species causes the formation of a positively charged ion. In addition, molecules are neutral species with an even number of electrons that are paired two by two in the orbitals. When one of these is removed, there is a remaining odd number,... 

The production of ions from neutral compounds and the examination of how these ions subsequently fragment is fundamental to mass spectrometry. Neutral sample molecules can be ionized by a variety of processes. The most important of these for the production of positively charged species is the removal of an electron or the addition of one or more protons to give either molecular ions (M+ ) or protonated molecular species (M+nH)"+. This initial stage of ionization is often followed by fragmentation to produce ionized fragments, fragment ions . 

The heat of formation of a positive ion in the gas phase is obtained by taking the heat of formation of the corresponding neutral species and adding the energy required to remove an electron from the molecule, i.e. the ionization energy24 ... 

A common experimental situation is the electrolysis of a neutral species to form an ion. The one-electron oxidation of ferrocene to ferricenium is an example of such a process. Since the current arises from the flux of a neutral to the electrode, the diffusion-limited current is unaffected by lowering the electrolyte concentration (Fig. 12.5, left panel). However, evaluation of the diffu-sion/migration equations shows that the charged product of the electrochemical reaction is removed from the diffusion layer by ion migration while inert ions of opposite charge are drawn in by the process of migration, again to maintain electroneutrality [68]. 

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

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