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We report a joint negative ion photoelectron spectroscopy (NIPES) and quantum chemical computational study on glycine-chloride/bromide complexes (denoted Gly·X−, X = Cl/Br) in close comparison to the previously studied Gly·I− cluster ion. Combining experimental NIPE spectra and theoretical calculations, various Gly·X− complexes were found to adopt the same types of low-lying isomers, albeit with different relative energies. Despite more congested spectral profiles for Gly·Cl− and Gly·Br−, spectral assignments were accomplished with the guidance of the knowledge learned from Gly·I−, where a larger spin–orbit splitting of iodine afforded well-resolved, recognizable spectral peaks. Three canonical plus one zwitterionic isomer for Gly·Cl− and four canonical conformers for Gly·Br− were experimentally identified and characterized in contrast to the five canonical ones observed for Gly·I− under similar experimental conditions. Taken together, this study investigates both genericity and variations in binding patterns for the complexes composed of glycine and various halides, demonstrating that iodide-tagging is an effective spectroscopic means to unravel diverse ion-molecule binding motifs for cluster anions with congested spectral bands by substituting the respective ion with iodide. [ABSTRACT FROM AUTHOR]

The tetramer of bis(4‐di‐n‐butylaminophenyl)(pyridin‐3‐yl)borane [systematic name: 2λ4,4λ4,6λ4,8λ4‐tetrabora‐1,3,5,7(1,3)‐tetrapyridinacyclooctaphane‐11,31,51,71‐tetrakis(ylium)], C132H192B4N12, was synthesized unexpectedly and crystallized. Its structure contains an unusual 16‐membered ring core made up of four (pyridin‐3‐yl)borane groups. The ring adopts a conformation with pseudo‐S4 symmetry that is very different from the two other reported examples of this ring system. Density functional theory (DFT) computations indicate that the stability of the three reported ring conformations is dependent on the substituents on the B atoms, and that the pseudo‐S4 geometry observed in the bis(4‐dibutylaminophenyl)(pyridin‐3‐yl)borane tetramer becomes significantly more stable when phenyl or 2,6‐dimethylphenyl groups are attached to the boron centers. [ABSTRACT FROM AUTHOR]

Charge‐enhanced chiral thioureas were used in the organocatalysis of the Friedel–Crafts alkylation of indole with trans‐β‐nitrostyrene and the oxa‐Pictet–Spengler reaction of tryptophol and benzaldehyde. The effects of substoichiometric Brønsted acidic additives on the reaction conversions and enantiomeric ratios of these transformations were examined, and the role of these species in the mechanism of the latter reaction was explored using variable time normalization kinetics to elucidate the reaction order of the catalyst, cocatalyst, and reagents. A proposed pathway for the oxa‐Pictet–Spengler cyclization that involves matched and mismatched catalyst and cocatalyst pairs and an off‐cycle racemization of the latter species is provided. [ABSTRACT FROM AUTHOR]

Several charge‐containing TADDOL salts were synthesized and used as organocatalysts in asymmetric Diels–Alder and hetero‐Diels–Alder reactions. Their catalytic activity was found to exceed that of a noncharged analog while maintaining or improving upon the enantioselectivity. The enhanced activities of the TADDOL salts enabled them to act as presumed hydrogen bond donor catalysts in the Diels–Alder and hetero‐Diels–Alder reactions of 1,3‐cyclohexadiene with methyl vinyl ketone at 40°C and 2‐phenoxy‐1,3‐butadiene with ethyl glyoxylate at room temperature, respectively. Given the ionic nature of these charge‐activated catalysts, it also proved possible to recycle and reuse the TADDOL without chromatography or the need for a recrystallization. [ABSTRACT FROM AUTHOR]

Gas-phase acidity and hydrogen-deuterium (H/D) exchange experiments are carried out on the conjugate base of cysteine with four different deuterated alcohols. The results have shown that the side-chain thiol in cysteine is more acidic than the carboxyl group by 3.1 kcal [mao.sup.-1] and hence deprotonated cysteine is predicted to be a thiolate ion.

Density functional theory was used to examine the solvation number and aggregation state of several alkyllithium compounds in clusters with tetrahydrofuran molecules coordinated to each lithium atom. The number of coordinated solvent molecules in the monomer and dimer show significant temperature dependence, as does the aggregation state of the alkyllithiums.

A thermodynamic cycle is used to carry out several proton affinity, as well as electron-binding measurements, which are then used to effectively and accurately measure the cycloalkane and cycloalkene carbon-hydrogen (C-H) bond dissociation energies in the gas phase. The results show that the normally cited bond energies for such cyclic hydrocarbons are much smaller than their actual values, while a vast difference is observed between the actual and calculated values of their bond strengths.

The heat of hydrogenation of phenylcyclobutadiene is determined via a thermodynamic cycle by carrying out gas-phase measurements on 1-phenylcyclobuten-3-yl cation. The results are compared to G3, G3(MP2), and B3LYP computations and represent the first experimental measurements of the energy of a monocyclic cyclobutadiene.

A linear relation between delta-H(super degree) (sub acid)(HX), EA[X(sub .)], and BDE(HX) is shown for specific classes of compounds and only one of these quantities is needed to determine the others. The intercepts obtained from plots of delta-H(super degree) (sub acid)(HX) vs EA[X(sub .)] provide bond energies which correspond to BDE(HX) when EA[X(sub .)] = 0.

A negative ion photoelectron spectra resulting from the decarboxylation of nine zwitterionic pyridinium dicarboxylates (D(x,y)) is presented. The study shows that the loss of CO2 from the zwitterions and from oxygen-protonated OMP (orotidine 5'-monophosphate) is retarded by the presence of an additional anionic group. It is found that the formation of a zwitterion intermediate in the enzyme-catalyzed conversion of OMP to UMP (uridine 5'-monophosphate) has less energetic impact.

The alpha,2-, alpha,3- and alpha,4-dehydrophenoxide anions are regiospecifically generated by collisional activation of o-, m-, and p-nitrobenzoate. The alpha,2 and alpha,4 isomers are synthesized by reacting o-benzyne radical anion with carbon dioxide and electron ionization of p-diazophenol.

Mechanistic and energetic aspects for the conversion of camphor to 5-exo-hydroxycamphor by the compound I iron-oxo species of cytochrome P450 are discussed from B3LYP DFT calculations. The reaction occurs in a two-step manner along the lines that the oxygen rebound mechanism suggests.

Nine isomeric pyridinium dicarboxylate zwitterions are investigated by photoelectron spectroscopy and compared to their nonzwitterion counterparts. Observations revealed that in the nonzwitterion analogues, the Coulomb repulsion between the negative charge on the carboxylate group and the N lone pair is also significant.

The electron affinity of 3-tert-butyl-1-bicyclo [1.1.1] pentyl radical (14.8 plusminus 3.2 Kcal/mol) is measured by bracketing as well as the acidity of 1-tert-butylbicyclo [1.1.1] pentane (408.5 plusmns 0.9) is determined by the DePuy kinetic method. The bridgehead C-H bond dissociation energy (109.7 plusmns 3.3 Kcal/mol) is much greater than a typical tertiary C-H bond (~ 96 Kcal /mol) and more typical of an aromatic or alkene C-H bond.

A chemical model study of the ring scission of diastereomeric spiropentylcarbinyl radicals is described and two structures for the identity of the enzyme- catalyzed FAD adducts resulting from spiropentylacetic acid-CoA (SPA-CoA) are proposed. Two structures for the enzyme-catalyzed FAD adducts resulting from spiropentylacetic acid-CoA, a synthetic byproduct of fatty acid metabolism are proposed.

Research is done on the molecular properties and electronic structures for three isomers of oxocyclohexadienylidene, which were examined using multiconfiguration SCF (MCSCF) wave functions. It is concluded that the MCSCF(8,8)/6-31+G* electron spin densities for both ortho and para isomers are very close to the experimental values of the phenoxyl radical.

All three N‐methylated and N‐protonated hydroxypyridinium BArF4– salt isomers were synthesized and their hydrogen bond donating abilities were investigated. DFT and G4 theory computations along with IR spectroscopic measurements were found to be effective methods for predicting the catalytic activities of these O–H and N–H Brønsted acids. A UV‐vis titration approach for rapidly quantifying hydrogen bond donating ability revealed that carbon‐hydrogen bonds also can participate in electrostatic interactions, but the presence of multiple equilibrium complexes results in a limitation of this method. In the methylated series of hydroxypyridines, the ortho and para isomers displayed modest rate enhancements relative to the meta derivative. Protonation introduces a new acidic site and the ortho hydroxypyridinium ion salt is a significantly more active catalyst than all of the other species examined. This is indicative of bidentate activation by the N–H and O–H acidic sites, and suggests a new design strategy for improving charge‐enhanced catalysts. [ABSTRACT FROM AUTHOR]

Uncertainties and errors in enantiomeric excess determinations obtained by high performance liquid chromatography (HPLC) with a chiral column are evaluated with different peak resolutions and elution orders using (R)‐ and (S)‐ibuprofen standards. Five injections of each sample were made to reduce the variability in the data and each chromatogram was monitored at multiple wavelengths to facilitate the detection of chemical impurities. Using appropriate sample concentrations, the most favorable detection wavelengths, and default instrument parameters led to large errors (>10 %) whereas properly set integration values gave impressive reproducibilities (±0.5 % or better) and accuracies (<1 %) in the most favorable situations. Uncertainties and errors of up to±2.0 % and 5.2 % ee, respectively were also observed under separation conditions routinely reported in chemistry journals. This study aims to provide a practical guide to the accuracy and precision that can be achieved with HPLC, and suggestions for obtaining reliable results. [ABSTRACT FROM AUTHOR]

Deprotonation of 2-adamantanone in the gas phase has produced the corresponding [beta]-enolate anion. An attempt to prepare the [gamma]-anion has resulted in the formation of its ring-opened isomer, that is, deprotonated 7-methylenebicyclo[3.3.1]nonan-2-one.

Five CH[B.sub.11][X.sub.6][Y.sub.5.sup.-] carborane anions from the series X - Br, Cl, I and Y = H. Cl, C[H.sub.3] are generated by electrospray ionization and their reactivity with a series of Bronsted acids and electron transfer reagents are examined in the gas phase. The studies have shown that it is the weak H-(CH[B.sub.11][Cl.sub.11]) BDE compared to the strong BDE of [(1-[C.sub.4][F.sub.9]S[O.sub.2]).sub.2]N-H that has accounted for the greater acidity of carborane acids.

Hydrogen bonds are the dominant motif for organizing the three-dimensional structures of biomolecules like carbohydrates, nucleic acids and proteins and have served as templates for proton transfer reactions. The computations in dimethyl sulfoxide on a series of polyols have shown that multiple hydrogen bonds to a single charged center have led to enhanced acidities and a new class of Bronsted acids is described.

The observation of both conjugate bases for tyrosine in the gas phase is described. The equilibrium proportions of the corresponding phenoxide and carboxylate anions along with a gas-phase equilibrium acidity determination of tyrosine and the isomeric compositions of deprotonated tyrosine and p-hydroxybenzoic acid formed electrospray ionization are reported.