Complexes ion-neutral

Perhaps the first suggestion of INCs came from Rylander and Meyerson. [172,173] The concept that the decomposition of oxonium and immonium ions involve INCs (Chap. 6.11.2) was successfully put forth by Bowen and Williams, [143,157,158,167,174] and the analogies to solvolysis were described by Morton. [168] Nonetheless, mass spectrometrist were too much used to strictly unimolecular reactions to assimilate such a concept without stringent proof. 

Conclusive evidence for INCs was first presented by Longevialle and Hotter [175,176] who demonstrated the transfer of a proton from an imine fragment to an amino group located on the opposite side of the rigid skeleton of bifunctional steroidal amines. [176] Such a proton transfer cannot proceed without the intermediacy of an INC otherwise, a conventional hydrogen shift would have bridged the distance of about 10 m between the respective groups which is about five times too far. 

Proton transfer will be prevented when the initial fragments separate too rapidly for the partners to rotate into a suitable configuration. Here, the lower limit for the intermediate s lifetime can be estimated to be 10 s. The competition between the 

Consider the dissociation of an ion AM that may either dissociate to form the fragments and M or the INC [A , M] allowing free mutual rotation and thus reorientation of the particles. Within the INC, A and M can recombine only if they attain a well-defined mutual orientation, i.e., the system has to freeze rotational degrees of freedom. Such a configuration allowing covalent bonds to be formed is termed locked-rotor critical configuration [169-171,177] and any reac- 

A species can be considered as an INC if its lifetime is long enough to allow for other chemical reactions than the mere dissociation of the incipient particles. This is the minimum criterion that has to be fulfilled to term a reactive intermediate an ion-neutral complex, because otherwise any transition state would also represent an INC. [171,178] In addition, the reorientation criterion [29,169] should be met, 

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Noncovalent isomeric 2-butyl ion/toluene complexes. As pointed out in the previous section, key features of ion-neutral complexes, such as the mutual orientation of their components and their evolution dynamics, usually escape precise determination because of intrinsic limitations of the available experimental methodologies. This lack of information is particularly unsatisfactory since, in principle, the nature and the dynamics of an ion-neutral complex may determine its evolution to products and, thus, the reaction selectivity. Filippi and coworkers" recently... 

Not all ionization methods rely on such strictly unimolecular conditions as El does. Chemical ionization (Cl, Chap. 7), for example, makes use of reactive collisions between ions generated from a reactant gas and the neutral analyte to achieve its ionization by some bimolecular process such as proton transfer. The question which reactant ion can protonate a given analyte can be answered from gas phase basicity (GB) or proton affinity (PA) data. Furthermore, proton transfer, and thus the relative proton affinities of the reactants, play an important role in many ion-neutral complex-mediated reactions (Chap. 6.12). 

Veith, H.J. Gross, J.H. Alkene Loss From Metastable Methyleneinunonium Ions Unusual Inverse Secondary Isotope Effect in Ion-Neutral Complex Intermediate Fragmentations. Org. Mass Spectrom. 1991,26, 1097-1105. 

Studying the competition of McLafferty rearrangement either with charge retention or charge migration and double hydrogen transfer has revealed that ion-neutral complex intermediates (Chap. 6.12) can also play a role for the latter two processes. [102]... 

The intermediacy of ion-neutral complexes is neither restricted to even-electron fragmentations nor to complexes that consist of a neutral molecule and an ion. hi addition, radical-ion complexes and radical ion-neutral complexes occur that may dissociate to yield the respective fragments or can even reversibly interconvert by hydride, proton or hydrogen radical shifts. Many examples are known from aliphatic alcohols, [180-183] alkylphenylethers, [184-187] and thioethers. [188]... 

Bowen, R.D. Ion-Neutral Complexes. Accounts of Chemical Research 1991, 24, 364-371. 

Bowen, R.D. The Role of Ion-Neutral Complexes in the Reactions of Onium Ions and Related Species. Org. Mass Spectrom. 1993,25,1577-1595. 

Morton, T.H. The Reorientation Criterion and Positive Ion-Neutral Complexes. Org. Mass Spectrom. 1992, 27, 353-368. 

Longevialle, P. Ion-Neutral Complexes in the Unimolecular Reactivity of Organic Cations in the Gas Phase. Mass Spectrom. Rev. 1992,11, 157-192. 

McAdoo, D.J. Hudson, C.E. Ion-Neutral Complex-Mediated Hydrogen Exchange in Ionized Butanol a Mechanism for Nonspecific Hydrogen Migration. Org. Mass Spectrom. 1987, 22, 615-621. 

Hammerum, S. Formation and Stabilization of Intermediate Ion-Neutral Complexes in Radical Cation Dissociation Reactions. J. Chem. Soc., Chem. Commun. 1988, 858-859. 

Traeger, J.C. Hudson, C.E. McAdoo, D.J. Isomeric Ion-Neutral Complexes Generated From Ionized 2-Methyl-propanol and n-Butanol the Effect of the Polarity of the Neutral Partner on Complex-Mediated Reactions. J. Am. Chem. Soc. Mass Spectrom. 1991, 3,409-416. 

Zappey, H.W. Ingemann, S. Nibbering, N.M.M. Isomerization and Fragmentation of Aliphatic Thioether Radical Cations in the Gas Phase Ion-Neutral Complexes in the Reactions of Metastable Ethyl Propyl Thioether Ions. J. Chem. Soc., Perkin Trans. 2 1991, 1887-1892. 

Coordina- tion Number Shape Ligand Structure/Formula Name of complex ion/neutral complex... 

A potential O-atom donor molecule, N2O, has been allowed to react with SiH+ to probe the formation of HSiO+, a higher energy isomer of SiOH+. The expectations were fulfilled (equation 13)43, as tested by reaction with a base capable of deprotonating HSiO+ but not SiOH+. The formal O-atom insertion product, SiOH+, was ascribed to a proton shuttle mechanism which is dominant when OX is SO2 and CO2 (equation 14). In fact, with these two neutrals the formation of HSiO+ and X as bare species is somewhat endothermic and the proton transfer process within the ion-neutral complex, driven by the stability of SiOH+, is allowed by the proton affinity (PA) of X which is intermediate between those of the Si and O sites of SiO. On the other hand, when O2 is used as the neutral reagent this pathway is not accessible and HSi02+ is the only observed product ion. 

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