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A Huisgen 1,3-dipolar cycloaddition 'click chemistry' was employed to immobilize azido sugars (mannose, lactose, [alpha]-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and [alpha]-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose--Con A; ECL--lactose, ([alpha]-Gal--anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 [+ or -] 2.8) x [10.sup.5] and (3.9 [+ or -] 0.2) x [10.sup.6] [M.sup.-1] measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and (x-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 [+ or -] 2.4) x [10.sup.6] and (6.7 [+ or -] 3.3) x [10.sup.6] [M.sup.-1], respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes.

O-type variations on C-H bond dissociation energies were studied.

The first detailed thermodynamic analysis in terms of the driving forces for ach basic step for the nitric oxide (NO)-initiated reaction with 3,6-dibromocarbazolide is presented. It is shown that an electrophilic combination of NO with 3,6-dibromocarbazolide to form the incipient radical anion, followed by electron transfer from the latter to NO, represents the most feasible mechanism. Electron transfer from the electron-rich species to NO may be incorporated when the substrate is a better electron-providing species.

Research was conducted to examine the role of adjacent onium cations and remote substituents on the H-A+ bond equilibrium acidities in dimethyl sulfoxide solution. The study is an extension of previous investigation on ylide thermodynamic stability scale and its implication for the importance of resonance effect on ylide stabilities. Results suggest that part of the stabilization in the phosphonium and sulfonium ylide cases arises from the backbonding stabilization involving the o* and/or 3d orbital participation.

Equilibrium acidities in DMSO for phenylhydrazine, five p-substituted derivatives, 1,2-diphenylhydrazine and 1,1,2-triphenylhydrazine were measured. The bond dissociation enthalpies (BDEs) of their acidic N-H bonds were estimated. The alpha-N-H bonds in CHsub3CONHNHsub2, PhCONHNHsub2, NHsub2NHCOsub2Et and PhSOsub2NHNHsub2 hydrazides were more acidic than the alpha-N-H bonds in corresponding amides, and the BDEs were weaker.

Bond dissociation energies of the acidic C-H bonds in 13 alpha-substituted 9-mehtylanthracenes and 11 10-substituted methylanthracenes. This included equilibium acidity (pKHA), reduction potential Ere(HA), oxidation potential Eox(HA), and oxidation potential of conjugate anions Eox(A-) in dimethyl sulfoxide solution. Equilibrium acidities were linearly correlated with Hammettsigma negative constants. Combinations of equilibrium acidities were used to determine homolytic bond dissociation energies.

The delta G(sub hydride) (R+) data for some stable carbocations and less stable aromatic carbocations derived from substituted toluenes, fluorenes and 9-methylanthracenes are reported. The computation of hydride affinities of organic cations was based on two equations derived from thermochemical cycles. Linear correlations were observed between hydride affinities and solution electron affinities of hydride acceptors. Correlations between delta G(sub hydride)(R+) and pK(sub R+) of corresponding carbinols provide convenient estimates of each other as long as the other is known.

Bond dissociation energies and hydronium ion concentrations at equilibrium of benzylic carbon to hydrogen bonds in dimethyl sulfoxide are presented. Nineteen triphenylmethanes, three dihydroanthracenes and nine xanthenes were used in the experiment. The resonance effect due to the solvation of a substituent induced a conformational alteration to allow for conjugative overlap of the anion and the substituents. The effect of substituents far from the carbanion was found to be negligible.

A thermodynamic study of the cleavage of carbon-sulfur bonds involves the analysis of the enthalpies of reactions between six thiophenoxides and fiveresonance-stabilized carbenium ions. C-S bond cleavage is of interest in the environmentally-critical desulfurization of coal. A battery of calorimetric andvoltammetric tests yield correlated data on the heats of heterolysis and homolysis, redox potentials and heats of entropies of the various processes involved in the reactions. These are presented and discussed in detail.

Alpha-sulfonium groups are radical stabilizing rather than radical destabilizing, as gleaned from theoretical calculations in an examination of the radical substituent effects of the alpha-sulfonium groups. Results showed that the radical-stabilizing effects of the alpha-dialkylsulfonium groups are smaller and with larger steric hindrance than those for the alpha-RS groups. They were also found to be associated with the free lone pair electrons of the sulfur atom in the sulfonium groups. The latter were found to be able to form a two-center three-electron bond with the unpaired electron of the radical.

The first-ever Y-nitric oxide (NO) bond energy scale, where Y is the atom to which NO is attached, is established by direct calorimetric measurements and electrochemical data for three types of N-nitroso compounds. These bond scales establish a technique for determining the dissociation energy of Y-NO bonds in solution and pave the way for developing a complete data set of Y-NO bond energies for a wider range of organic and inorganic compounds.

Examines equilibrium acidities and homolytic bond dissociation enthalpies of the acidic C-H bonds in As-substituted triphenylarsonium and related cations. Examination of the effects of a-triphenylarsonium groups on the equilibrium acidities; Results and discussion of the findings.

Reports on the comparison between free radicals and carbenium ions as hydride ion acceptors. Hydride affinities of free radicals obtained from thermochemical cycle; Difference in free energy changes; Estimation of absolute values for the hydride affinities of several models.

Studies the hydride affinities of carbenium ions in acetonitrile and dimethyl sulfoxide solution. Use of equations derived from thermochemical cycles; Errors associated with the determination of the reversible electrode potentials; Stable carbenium ion in dimethyl sulfoxide solution; Cancellation of errors due to kinetic shifts of the experimental potentials from the reversible values.

Presents information pertaining to the formal hydride transfer reactions regarding the reduced nicotinamide adenine dinucleotide (NADH) models, referencing to various cations and quinones. Possibility of a hybrid mechanism; How reduction potentials were obtained;Evaluation of the bond dissociation free energy of the 9-C-H bond in N-methylacridinium ion (AcrH+).

Studies the free energy hydride affinities of quinones in dimethyl sulfoxide solution. Use of thermochemical cycle; Determination of the pKa of hydroquinone monoanions; Observation of the values of deltaGhydride(Q)DMSO.

Controlling product selectivity in successive reactions of the same type is challenging owing to the comparable thermodynamic and kinetic properties of the reactions involved. Here, the synergistic interaction of the two phosphoryl groups in bisphosphine dioxides (BPDOs) with a bromo-phosphonium cation was studied experimentally to provide a practical tool for substrate-catalyst recognition. As the eventual result, we have developed a phosphonium-catalyzed monoreduction of chiral BPDOs to access an array of synthetically useful bisphosphine monoxides (BPMOs) with axial, spiro, and planar chirality, which are otherwise challenging to synthesize before. The reaction features excellent selectivity and impressive reactivity. It proceeds under mild conditions, avoiding the use of superstoichiometric amounts of additives and metal catalysts to simplify the synthetic procedure. The accessibility and scalability of the reaction allowed for the rapid construction of a ligand library for optimization of asymmetric Heck-type cyclization, laying the foundation for a broad range of applications of chiral BPMOs in catalysis.

Deoxygenation of phosphine oxides is of great significance to synthesis of phosphorus ligands and relevant catalysts, as well as to the sustainability of phosphorus chemistry. However, the thermodynamic inertness of P═O bonds poses a severe challenge to their reduction. Previous approaches in this regard rely primarily on a type of P═O bond activation with either Lewis/Brønsted acids or stoichiometric halogenating reagents under harsh conditions. Here, we wish to report a novel catalytic strategy for facile and efficient deoxygenation of phosphine oxides via successive isodesmic reactions, whose thermodynamic driving force for breaking the strong P═O bond was compensated by a synchronous formation of another P═O bond. The reaction was enabled by P III /P═O redox sequences with the cyclic organophosphorus catalyst and terminal reductant PhSiH 3 . This catalytic reaction avoids the use of the stoichiometric activator as in other cases and features a broad substrate scope, excellent reactivities, and mild reaction conditions. Preliminary thermodynamic and mechanistic investigations disclosed a dual synergistic role of the catalyst.

The metal-free catalytic C-F bond activation of polyfluoroarenes was achieved with diazaphospholene as the catalyst and phenylsilane as the terminal reductant. Density functional theory calculations suggested a concerted nucleophilic aromatic substitution mechanism.

The equilibrium acidities for several series of structural and electronic different organic acids were measured in 3-pyrrolidinium-based aprotic and protic ionic liquid (IL) analogues, that is, [Bmpy][NTf 2 ], [BpyH][NTf 2 ], and [PyH 2 ][NTf 2 ], by the UV-Vis method. The acidities of neutral acids are found to be much stronger in the protic ILs (PILs) than aprotic ILs (AILs), and the acidifying effect in the two PILs roughly increases proportionally to the number of protons in the cation of the PIL. On the other hand, interestingly, the cationic N + -H acids exhibit similar acidities in [Bmpy][NTf 2 ] and [BpyH][NTf 2 ] but much weaker than those in [PyH 2 ][NTf 2 ]. The Hammett ρ values for the acidic dissociation of para-substituted benzoic acids in two PILs are about the same as that in water (1.00) but significantly smaller than that in the AIL [Bmpy][NTf 2 ] (2.66). The correlations between the acidities in the PILs and water show double-linear relationships with different slopes and intercepts for the neutral and cationic acids. These, together with previous observations in the PILs [DBUH][OTf] (DBU = 1,5-diazabicyclo(5.4.0)-5-undecene) and EAN (ethylammonium nitrate), clearly indicate that the structure of the cation plays a subtle but a crucial role on sensing the electronic nature of solutes and strongly affects the solvation behaviors of PILs.

Because of their unique biological, physical, and chemical properties, organofluorine compounds play an increasingly important role in numerous areas of chemistry and everyday life. However, although fluorine is the most abundant halogen in the earth's crust and ranks 13th in abundance among all elements, naturally occurring organofluorine compounds are rare. Consequently, there is a growing demand for the development of safe and efficient reagents and selective synthetic methodologies for the introduction of fluorine or fluorine-containing groups into organic compounds. A wide variety of shelf-stable electrophilic fluorinating and fluoroalkylating reagents have been developed in the past decades. Some of them have also been shown to act as radical sources. These versatile reagents have promoted revolutionary advances in synthetic fluorine chemistry. These developments of novel reagents and the choice of suitable reagents for new reactions have relied largely on the traditional trial-and-error approach because (i) structure-reactivity relationships and mechanisms of reactions of these reagents are sparse and (ii) the rules that govern the synthesis of non-fluorinated analogues cannot necessarily be transposed to fluorinated compounds ( Cahard , D. ; et al. Chem. Soc. Rev. 2014 , 43 , 135 ), since organic fluorine compounds often exhibit unusual properties. Over the past several years, our studies have aimed at establishing comprehensive cation and radical donor scales of electrophilic F, CF 3 , and SCF 3 transfer reagents. We have also developed detailed structure-reactivity relationships. We used density functional theory calculations to systematically investigate the energies required to heterolytically cleave the Y-F/CF 3 /SCF 3 bonds to donate electrophilic F/CF 3 /SCF 3 groups. We found that these energies can be used as convenient indicators of the relative electrophilic fluorinating/trifluoromethylating/trifluoromethylthiolating strengths of these reagents. We have constructed the first comprehensive cation donor scales for electrophilic F, CF 3 , and SCF 3 transfer reagents. In collaboration with Mayr group, we experimentally determined the electrophilicity parameters of SCF 3 transfer reagents and demonstrated the importance of intrinsic barriers for predicting their kinetic reactivity. The recognition of the novel application of a few traditional electrophilic reagents as radical sources prompted us further to construct comprehensive radical donor scales of electrophilic F, CF 3 , and SCF 3 transfer reagents. We identified a series of potential new radical F, CF 3 , and SCF 3 donors. Single electron transfer was found to exhibit a substantial effect on activation of the Y-CF 3 /SCF 3 bonds, significantly facilitating the release of CF 3 /SCF 3 radicals. This Account summarizes computational and experimental accomplishments from our group and others to establish the missing links between structure and reactivity for these reagents. Our results pave the way toward the rational optimization, design, and prediction of novel electrophilic fluorinating and fluoroalkylating reagents and new reactions.

Axially chiral amides are usually found in many biologically active compounds and are useful ligands in asymmetric catalysis. Herein, by using the dynamic kinetic resolution approach, an asymmetric allylic alkylation reaction of racemic amide naphthols is disclosed, which leads to generation of the axially chiral naphthamides in good to excellent yields (up to 97%) and enantioselectivities (up to 96:4 e.r.). Density functional theory was used to gain a theoretical understanding of the enantioselectivities in this reaction.

Green and efficient C-C bond cleavage/cyanoalkylation of quinoxalin-2(1 H)-ones and other heteroarenes under visible light or sunlight irradiation is described. The reaction proceeds under mild conditions at room temperature without transition-metal catalysts and extra bases. Notably, the products enable facile transformations to various significant organic compounds.