Distonic ions

Example Propyl and pentyl losses from 2-ethyl-cyclohexylamine molecular ion, IVP = 127 (odd m/z) are competitive (Fig. 6.12). Pentyl loss, m/z 56 (even ffj/z), is favored over propyl loss, m/z 84 (even m/z), in accordance with Stevenson s rule. The peak at m/z 98 may be explained by ethyl loss due to a minor contribution of 1,4-H shift, i.e., from 3-position instead of the predominant 1,5-H shift from 2-position. The [M-CHs] peak, m/z 112, is accompanied by a [M-NHs] signal, m/z 110, which is typicd of primary (and to lower extent) secondary amines. 

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In the intermediate generated by the first a-cleavage of cyclohexyl compounds charge and radical are not located at the same atom as is the case with molecular ions, but at distant positions. The term distonic ion was derived from the Greek word for separate to describe such ionic species. [40] Distonic ions represent an ionic class of their own. [40-42]... 

Definition A distonic ion is a positive radical ion, which would formally arise by ionization of a zwitterion or a diradical, by isomerization or fragmentation of a classical molecular ion, or by ion-molecule reactions. Consequently, distonic ions have charge and radical at separate atoms in a conventional valence bond description. [42,43]... 

However, bearing charge and radical at separate sites is not a sufficient condition for an ion to be denoted distonic, e.g., the ethylene molecular ion may be written as such, but the corresponding neutral is not best represented as zwitterion and therefore the ethylene molecular ion by definition is not a distonic ion ... 

The expressions nonclassical and hypervalent ion have also been used by some authors to describe distonic ions, but these are incorrect and thus should no longer be used. The term ylidion is limited to species where charge and radical are at adjacent positions. Thus, to describe the distance between charge and radical site, the terms a- (1,2-) distonic ion, p- (1,3-) distonic ion, y- (1,4-) distonic ion, and so forth are now in use [42,43]... 

Cleavage of a bond without immediate dissociation of the precursor radical ion is one way for the generating distonic ions. Isomerization of molecular ions by hydrogen radical shift frequently leads to distonic ions prior to fragmentation and. 

Although amine-derived distonic ions have been mainly presented up to here, the occurrence of distonic ions is by far not restricted to this compound class. Instead, distonic ions are of high relevance as these ions play an important role as the cen-... 

While the concerted pathway has been preferred in early publications on the subject, evidence for a stepwise mechanism involving distonic ion intermediates is presented in more recent work taking kinetic isotope effects into account. [90] This is also in agreement with the postulation that reactions involving multiple bonds are generally stepwise processes. [37,91] Nevertheless, this question is still a matter of debate. [90]... 

Localization of an unpaired electron in the framework of a definite molecular fragment can sometimes lead to the formation of ion-radicals with spatially separated charge and radical sites. They can be considered free radicals with an appended, remote charge. These species form a particular class of distonic ion-radicals. Distonic is from the Greek word diestos and the Latin word distans, both meaning separate. Yates et al. (1984) introduced this term for ions that formally arise by the removal of an electron from a zwitterion or a biradical. 

Research on spin-charge separation in distonic ion-radicals has been carried out in recent years with an emphasis on theoretical calculations. Experiments were performed to prove their existence and observe their behavior in a mass spectrometer chamber. The next step is likely to emphasize the synthesis of the distonic ion-radical salts, which could be stable under common conditions. Applications of the salts would be possible in creating magnetic, conductible media and other materials possess practically useful properties. The attractive strength of distonic ion-radicals is that they can enter ionic reactions at the charged site and radical reactions at the radical site. Success in this direction can open a new window in terms of organic reactivity. 

It would be expedient to widen synthetic applications of distonic ion-radicals. In principle, they allow developing dual reactivity—at the sites of radical unsaturation and, separately, of charge localization. The sterical aspects of ion-radical organic chemistry can also be estimated as intriguing, but they are insufficiently developed. The so-called confined ion-radical organic chemistry promises serious perspectives, too. 

Distonic ions reacting primarily at the radical center provide the opportunity to study free radical reactions in the gas phase by MS. For example, 4-dehydroanilin-ium ions (37 +, m/z = 93) were generated by multiple low-energy collisions of chloro-, bromo-, or iodoanilinium ions (36+, m/z = 220) with argon. This distonic species reacted with dimethyl sulfide by abstraction of thiomethyl (MeS ), that is, as a reactive radical with an inert charge site. However, 37 + can be deprotonated by pyridine. 2° ... 

Many distonic radical ions are involved in unimolecular dissociation reactions. For example, the McLafferty rearrangement of carbonyl compounds proceeds by C—C bond cleavage of distonic ions. ° Alternatively, bond-cleavage reactions of cyclic molecular ions may generate distonic ions (see above).For example, C—C bond cleavage of cyclic ketone molecular ions (e.g., 61 " ) generates 62 ". ... 

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