Gas-phase anions

Sn2 Reactions. Given its central role in the development of modem physical organic chemistry, it is no surprise that the Sn2 substitution reaction is the most widely studied of all gas-phase anionic processes. In a classic study, Ohn-... 

The hydrogen/deuterium exchange has proven to be an extremely valuable tool for the analysis of gas-phase anion structures and reactivity184-187. The data which are reported in Table 25 suggest an absolute gas-phase basicity (AG°) of H2C=CH—S- is 341 ... 

Most gas-phase atoms can capture an electron to form a gas-phase anion, e.g., Cl(g) + e —> CF, AE = -3.61 eV. The electron affinity (EA) of Cl is taken to be +3.61 eV. Electron affinities for some other atoms are given in Table 7-2. In general, atoms with nearly completed p-shells have the highest electron affinities those with completed s- or p-outer shells have negative electron affinities, i.e., they do not accept an extra electron. 

Gas phase anions may be generated by electron impact via one of the following three processes ... 

FIGURE 5.7 Semi-empirical PM3 energy-minimized structures of Suwannee fulvic acid.69 Structure 1 as (a) gas-phase, neutral, (b) gas-phase anion, and (c) aqueous-phase anion. (Note that the H20 molecules of solvation in the model have been removed from this figure for clarity.) H-bonding affects the conformation of the molecule, and both deprotonation and solvation strongly affect the H-bonding that forms. 

In the condensed phase, where the lifetimes of the anions are increased and their wavefunctions should be considerably more localized, all the anion states should experience considerable reorganization. In other words, when compared to the condensed phase anions, the high-lying gas phase anions are "non-relaxed" and the low-lying anions essentially "fully relaxed". Clearly, any anion state which lives sufficiently long to display structure due to nuclear motion will be essentially fully relaxed electronically. 

Experiments and DFT calculations have been used to examine the binding of 02 with gas phase Aun anions.156 159 For the gas phase anions, 02 readily binds to clusters with even n but clusters with odd n are relatively inert for <20.157,158 In the gas phase, Aun anions are found to be planar for n< 13.159... 

In mass spectrometry, the main types of anions arising from ionization of a neutral molecule M are deprotonated ions, [M — H]. Key energies associated with the formation and stability of these gas-phase anions are the anion proton affinity (APA) and the electron affinity (EA). 

The problem of long range Interactions between widely separated subunits In molecules Is of Importance In many areas of chemistry and biology. Although many studies have appeared characterizing these Interactions In excited states and cationic species, very little has been done In gas-phase anions. For these reasons we have undertaken a study of such Interactions In nonconjugated dienes and dlones. Several of the dienes we have examined (35) are shown below ... 

Nucleophilic Reactivity in Gas-Phase Anion-Molecule Reactions... 

The gas-phase anion-molecule reactions of organophosphorus and organosulphur species have been the subject of a previous review. As noted in that review, the gas-phase anion chemistry of organophosphorus compounds represents a relatively unexplored area, especially when compared with positive ion studies. Only modest progress has been made since then. 

However, if Ae material is an alloy containing at least two elements, then the more active element oxidizes first and its cations react with the gas-phase anions to form the initial oxide, sulfide, carbide, nitride, and so on. Other elements in the alloy may react afterward to form other surface compounds. Consequently, the surface scale may be a combination of phases, which may be identified by X-Ray diffraction and revealed by scanning electron microscopy (SEM). 

Figure 17 Qualitative depiction of how solvation might alter the solution-phase potentials (hroken curves) of M and M", relative to the corresponding gas-phase potentials (solid curves). The shaded region indicates the resonance width of the gas-phase anion. Adapted with permission from Ref. 187 copyright 2004 Elsevier.

Bonding in Gas-Phase Anions. An Ion Cyclotron Resonance Determination of Fluoride Binding Energetics to Broensted Acids from Gas-Phase Fluoride Exchange Equilibrium Measurements. 

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