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The interest over the magnitude of the conjugation effect in the allyl cation CH(sub 2) = CH-CH(sub 2)(super +) and anion CH(sub 2) = (CH-CH(sub 2)(super -) is revived using an empirical extrapolation approximation. This case is revisited by explicitly calculating the Pauling-structure to the delocalized energy-minimum state of a conjugated system, using a newly developed block-localized wave function (BLW) method.

Photochemical reduction of several 4-picolyl- and N-methy-4-picolinium esters is examined using product analysis, laser flash photolysis, and fluorescence quenching. It is demonstrated that the radical (anions) formed in these reactions readily fragment t yield a carboxylic acid and a 4-pyridylmethyl radical intermediate.

Directed syntheses of spirocyclic nucleosides featuring adenine and guanine as the nucleobases is successfully developed. The configurational assignments are based on the thermal interconversions and supporting MM3 steric energy calculations.

The diastereofacial selectivity of 2-methyl-5-X-adamant-2-yl cations toward methanol is investigated in the gas phase at 750 Torr and in the 40-120 degreeC temperature range and compared with that of I(sub F) (X = F) and I(sub Si) (X = (CH(sub 3))(sub 3)Si) measured previously under similar conditions. Detailed analysis of the energy surface of the I(sub Me) (X = CH(sub 3)) ion reveals that the activation barrier of its syn addition to methanol is significantly lower than that of the anti attack.

Diastereofacial selectivity in tertiary 2-adamantyl cations was investigated in the gas phase.

Chiral ion-dipole pairs were studied in terms of hindered inversion.

Research was conducted to study the regio and stereochemistry of the nucleophilic attacks on chiral allylic alcohols in the gas phase. Gas chromatographic analyses of isomeric ethers were determined at 40 degrees C and 720 Torr from the attack of free cations while homochiral diastereomers were eluted. Results showed that the occurrence of possible free-radical pathways in the irradiated samples was strongly influenced by the presence of an efficient thermal radical scavenger.

Research was conducted to study the mechanism and kinetics of the racemization and regioisomerization of O-methylated (S)-trans-4-hexen-3-ol in the gas phase. Activation parameters were determined and compared with the racemization and regioisomerization of O-protonated (S)-trans-4-hexen-3-ol. The formation of hydrogen-bonded complex was evaluated by kinetic factors and by the specific conformation of their oxonium ion precursors.

Chemical research shows that phosphorus molecules in space are created via the reactions PFn+(n=1,2) + H20, CH3OH, and NH3. Fourier-transform ion cyclotron resonance mass spectrometry and G2 proton loss energy analysis provide a profile of the phosphorus atom's kinetics and thermochemical nature. Oxygen- and nitrogen-containing phosphorus ions including [H, P, O]+ and [H2, P, N]+ ions are created via the above reactions.

O-protonated (S)-trans-4-hexen-3-ol (IS) exhibits a higher rate constant in gas phase racemization at temperatures of between 40 and 120 degrees centigrade than during its isomerization (1.0-9.9 x 10(super 6) s-1). The structure of IS determines the speed in which structured complexes are produced, their nature and stability. The nature and occurrence of intimate-ion pairs in acid-catalyzed racemization and isomerization of optically active alcohols would seem to accommodate prior research evidence.

The proton and electron transfer efficiencies of HO3+ and H2O3+ ions with various inorganic and organic substrates were used to examine the thermochemistry of the ions and of the HO3 radical. Results of kinetic experiments show that ground-state HO3 (2A) radical is thermochemically stable toward dissociation to HO-(2II) and O2(3sigma(sub g)-). They also show that it is can be involved in major atmospheric reactions. These results are in contrast with many theoretical measurements.

An FT-ICR study, based on evaluation of the equilibrium constant of the reaction between H2O-NO2(+) and CH3OH, examines thermochemical quantities associated with nitric acid and methyl nitrate. The resulting data and the proton affinity of methyl nitrate, determine proton affinity of nitric acid and binding energies of water and methanol to NO(2+). Proton affinity of nitric acid is higher than that of methyl nitrate.

An analysis of the application of tritium, H, designated T, to the production of carbocations reveals that the suitable application of the T decay method resolves structural, reactivity and mechanistic issues regarding carbocations. The approach has potential in formulating kinetic and mechanistic correlations between gas-phase and condensed-phase ion chemistry. It facilitates the isolation of structurally diagnostic derivatives of the nucleogenic ions.

Nuclear-decay, radiolytic and FT-ICR methods were used with ab initio computations to analyze the structures, stabilities and isomerization patterns of C5H9+ ions emerging from gas-phase protonation of spiropentane. Early development of a corner-protonated spiropentane intermediate, where lifetime in the gas phase surpasses 7 times 10(super -9) seconds, was confirmed.

Ab initio and experimental methods were conducted on the proton affinity (PA) of hydrazoic acid. The study aimed to resolve the discrepancy between the value of 186.4 kcal/mol reported by Glaser and Choy in calculations done at the CISD (fc)/6-311G(df,p)//MP2(full)/6-31G* + delta-ZPVE (MP2(full)/6-31G*) level of theory and the previously obtained value of 176.6 kcal/mol at 298 K. Results revealed a PA of 180 plus or minus 2 kcal/mol for NH3, while Gaussian-1 calculations yielded a value of approximately 179.4 kcal/mol at 298 K. It was concluded that Glaser and Choy's reported PA value was overestimated.

One of the most studied feature of aromatic molecular clusters in the gas phase is the shift of the π*← π electronic transitions between the bare aromatic chromophore and its clusters. In the present ab initio complete active space self-consistent field study the coupling of the basis set superposition error and counterpoise procedure and a combination of Pople- and Slater-type Gaussian basis sets has been proven to reproduce quantitatively the gas-phase experimental shifts. The quantal results are here analyzed with respect to the electrostatic and polarization forces and electron density differences, and connected with the sign of the shifts of the electronic transitions. [ABSTRACT FROM AUTHOR]

The acid-catalyzed of C[H.sub.3][super 18]OH to 2-methylene-adamantanes bearing a chlorine atom in the 4-equatorial or 4-axial position is examined in the gas phase. The effects due to differential face salvation phenomena have come from the comparison of the present gas-phase results with those obtained from strictly related studies in solution.

The structure, stability and reactivity of proton-bound diastereomeric [[M.H.A.].sup.+] complexes between some amino acid derivatives and chiral tetra-amide macrocycles are examined in the gas phase by ESI-FT-ICR and ESI-ITMS-CID mass spectrometry. The enantioselectivity has reflected the stability difference between the relevant distereomeric transition structures.

Resonant two-photon ionization (R2PI) spectroscopy is used for studying the role of N-H...F and OH...N and dispersive interactions in the chiral recognition of R-1-phenyl-2,2,2-trifluoroethanol (F[E.sub.R]) toward the amines. The spectral differences have reflected the strength of noncovalent forces holding together the amine enantiomers and the chiral F[E.sub.R] chromophore.

Four cone resorc[4]arene octamethyl ethers tetrafunctionalized at the feet with valyl-leucine and leucyl-valine methyl esters are prepared. The four N-linked peptidoresorc[4]arenes have acted as synthetic receptors and are used for recognizing the homologue dipeptide by means of hydrogen bonds.

The investigation report of secondary 5-X-adamant-2-yl cations [I.sub.x] (X = F, Si[(C[H.sub.3]).sub.3] generated in the gas phase from protonation-induced defluorination of epimeric 2-F-5-X-adamantanes [I.sub.x] and their kinetic diastereoselectivity toward C[H.sub.3.sup.18]OH in the temperature range 40-160 degree Celsius is presented.

The kinetics and stereochemistry of the protonation-induced unimolecular isomerization of (R)-1-D1-3-(p-fluorophenyl)butane are investigated in the gas phase at 40-100 degree Celsius and 70-760 Torr. This process leads to the formation of the relevant meta and ortho isomers with partial racemization of the migrating sec-butyl moiety.

One- and two-color, mass selected R2PI spectra of the S1

Experimental gas-phase acidities are reported for a series of 3-substituted (X) bicyclo [1.1.1]pent-1-yl carboxyl acids. Various correlations are presented which clearly point to polar field effects as being the origin of the relative acidities.

The available computational data including Ignatyev and Sundius (IS's) suggested that the description of the transition structures of automerizaion is sensitive to the level of the theory employed. The gas-phase automerization for phenylium ion, observed in all decay experiments involves superexcited species.