Gas phase acidity and

Relationships between Hydration Energies and Gas-Phase Acidities and Basicities... 

Proton Transfer and Electron Transfer Equilibria. The experimental determination used for the data discussed in the above subsections of Section IV.B were obtained from ion-molecule association (clustering) equilibria, for example equation 9. A vast amount of thermochemical data such as gas-phase acidities and basicities have been obtained by conventional gas-phase techniques from proton transfer equilibria,3,7-12-87d 87g while electron affinities88 and ionization energies89 have been obtained from electron transfer equilibria. 

These models refer to reactions with the simplest nucleophile, H, both under neutral conditions and in the protonated form. Chemical reactivity can be strongly altered by catalytic effects acid/base catalysis is of particular importance. We regard the studies on ga phase acidities and on proton affinities discussed in the above sections to bear special significance for quantitative modelling of acid/base catalysis in the future. 

A wide range of thermochemical properties can be measured, including not only proton affinity or gas-phase basicity, but also electron affinity, ionization energy, gas-phase acidity and cation affinity Entropy changes upon attachment of an ion to a molecule are also accessible and provide information on both the nature of the bonding and fragmentation mechanisms in cluster ions, especially in biological compounds. Thermochemical determinations by the kinetic method also provide very useful structural information e.g., two-electron three-center bond has been observed in the gas phase by means of the kinetic method. " In the last years, the kinetic method has been also applied to characterize chiral ions in the gas phase. 

Table 2.5 Electron affinities of silyl radicals together with gas-phase acidities and bond dissociation enthalpies of silanes"...

Eatough DJ, Benner CL, Bayona JM, Richards G, Lamb JD, Lee ML, Lewis EA, Hansen LD (1969) Chemical composition of environmental tobacco smoke. 1 Gas-phase acids and bases. Environ Sci Technol 23 679-687... 

The overall goal of the proposed work is to broaden our understanding of nucleotide chemistry through gas-phase mass spectrometric and theoretical quantum mechanical studies. The objectives are twofold. First, the gas-phase acidity and nucleophilicity of... 

Cooks and co-workers developed an alternative method for the experimental determination of relative gas phase acidities and basicities. 

The early work on gas-phase acidities and basicities (Brauman and Blair, 1970 Brauman et al., 1971), obtained by probing the preferred direction of proton transfer reactions in the gas phase, established a benchmark in physical organic chemistry. The results pointed out, for example, that polarizability arguments could satisfactorily account for the smooth trends observed within a homologous series, unlike the -values in condensed media where solvation effects may reverse the relative orders of acidities and basicities. 

For reviews of methods used to measure the acidity of carbon acids, see Jones Q. Rev., Chem. Soc. 1971, 25, 365-378 Fischer Rcwicki Prog. Org. Chem. 1968, 7, 116-161 Reutov Beletskaya Butin. Ref. 11. Chapter I an earlier version of this chapter appeared in Russ. Chem. Rev. 1974, 43. 17-31) Ref. 6. For reviews on acidities of carbon acids, see Gau Assadourian Veracini Prog. Phys. Org. Chem. 1987, 16, 237-285 in Bunccl Durst Comprehensive Carbanion Chemistry, pt. A Elsevier New York, 1980, the reviews by Pcllcritc Brauman. pp. 55-96 (gas phase acidities) and Streitwicscr Juaristi Nebenzahl, pp. 323-381. 

Secondary isotope effects on gas-phase acidity and basicity 146... 

Bicycio[m. .0]alkenes (25 in. n) with the double bond linking the bridgehead carbons are another class of relevant compounds. Enthalpy-of-formation data are available for the m = n = 1 case through analysis of gas-phase acidity and electron-affinity measurements76, and for m = 2, n = 2, 3 and 4 from hydrogenation data54 from reaction in a thermochemically innocuous hydrocarbon solvent. Parallelling the earlier transalkylation reactions (equation 14), perhaps the simplest comparison we can make is to use the enthalpy of the reaction of the bicyclic species with ethylene to form two mono-cyclic ones. 

Other means of manipulating ions trapped in the FTMS cell include photodissociation (70-74), surface induced dissociation (75) and electron impact excitation ("EIEIO")(76) reactions. These processes can also be used to obtain structural information, such as isomeric differentiation. In some cases, the information obtained from these processes gives insight into structure beyond that obtained from collision induced dissociation reactions (74). These and other processes can be used in conjunction with FTMS to study gas phase properties of ions, such as gas phase acidities and basicities, electron affinities, bond energies, reactivities, and spectroscopic parameters. Recent reviews (4, 77) have covered many examples of the application of FTMS and ICR, in general, to these types of processes. These processes can also be used to obtain structural information, such as isomeric differentiation. 

Acidities and basicities of organic compounds are expected to be different in the gas phase and in solution. Whereas in the gas phase acidity and basicity are intrinsic properties of the individual molecules, in the liquid state these properties belong to the phase... 

Gas-phase acidities and basicities for many organic compounds are now available, primarily due to the development within the past decades of three new experimental techniques pulsed high-pressure i.e. 0.1... 1300 Pa) mass spectrometry (HPMS) [22, 23, 118], the flowing afterglow (FA) technique with a fast-flowing gas like helium in the pressure range of ca. 10 . .. 10 Pa [119], and pulsed electron beam, trapped ion cell, ion cyclotron resonance (ICR) spectrometry, carried out at ca. 10 ... 10 Pa [24-26, 115]. 

Burk, P. Koppel, I. A. Koppel, I. Leito, I. Travnikova, O. Critical test of pafor-mance of B3LYP functional for prediction of gas-phase acidities and basicities, Chem. Phys. Lett. 2000,323,482-489. 

Curves for the negative-ion states of H2 and L are chosen to illustrate the procedures for the homonuclear diatomic molecules. Curves for benzene and naphthalene are examples of excited states for larger molecular negative ions. These illustrate the relationship between gas phase acidities and thermal electron attachment reactions. Such correlation procedures can be applied to systematic predictions for many different problems. 

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