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The interaction of aryloxychlorocarbenes with dialkyl acetylenedicarboxylates is examined. Thermolyses of 3-aryloxy-3-chlorodiazirines in the presence of acetylenedicarboxylate results in the formation of unexpected polyfunctional 1,3-butadienes and 8-oxatricyclo[3.2.1.0(super 2.4)]oct-6-enes.

Results reveal that the active site of 1-aryl-1,4-dihydronicotinamide is at position 4 on the dihydropyridine ring for 2-methyl-5-nitroisoquinolium and at position 1 for tropylium and xanthylium cations. The former reactions proceed by direct one-step hydride transfer, while in the latter reaction the hydride transfer occurs via multistep reaction.

Research describes a biomimetic reaction for the synthesis of cyclo compounds using Hantzsch 1,4-dihydropyridine, instead of 1-Benzyl-1,4-dihydronicotinamide, in NAD(P)H mimic reactions. Results indicate that the procedure results in high yields of cyclopropane, indane, and exopin derivatives.

Nitric Oxide plays an important role in many striking discoveries of wide human physiological processes. Experiments conducted on four substituted derivatives of Hantzsch 1,4 dihydropyridines were treated by nitric oxide (NO) or its donor N-methyl-N-nitrosotoluene-p-sulfonamide (MNTS) to give the corresponding pyridine derivatives and its results are discussed.

Research evaluates the N-NO bond dissociation energies of the N-nitroso diphenylamine compounds and analogues in solution. Results show that in solution, homolysis rather than heterolysis of the N-NO bonds occurs and the bond activation is mediated by the reduction of one electron suggesting similar bond cleavage under both conditions.

Results suggest that the heterolytic N-H bond dissociation is largely favored to that of homolytic bond dissociation and the electron removal/addition from the parent molecule activates the N-H bond cleavage under alkaline pH conditions. Furthermore, the (N-H) homolysis is preferred over the heterolysis.

The one-electron oxidation potentials, p[K.sub.a] values, and bond dissociation energies of 118 important p- and o-dihydroquinones in DMSO are predicted by using DFT method and the PCM cluster continuum model. The studies have shown that all the five thermodynamic parameters have correlated well with the Hammett substituent parameters, indicating that the thermodynamic parameters are obtained as long as the structure of the hydroquinones is known.

The one-electron reduction potentials of the important p- and o-quinones in DMSO and C[H.sub.3]CN are predicted by using the PCM cluster continuum model. The knowledge about the redox potentials of the quinones is very useful for understanding the nature of chemical reactions of quinones, the designing of new electronic materials of quinones and the examining of biological activities of quinones.

A series of imines with various typical structures are prepared and the thermodynamic affinities of the imines to abstract hydride anions, hydrogen atoms and electrons, the thermodynamic affinities of the radical anions of the imines to abstract hydrogen atoms and protons and the thermodynamic affinities of the hydrogen adducts of the imines to abstract electrons in acetonitrile are determined. The studies have introduced the idea of a thermodynamic characteristic graph (TCG) of imines as an efficient oMolecule ID Cardo.

The first set of C-NO bond homolytic and heterolytic dissociation enthalpies in solution is obtained by using direct titration calorimetry combined with appropriate electrode potentials through thermodynamic cycles. The homolytic bond dissociation energy scale (BDEs) of the corresponding C-NO bonds in the gas phase is calculated and the C-NO and S-NO bond thermodynamic parameters are used for predicting the trend of NO transfer from C-nitroso substrates to thiols in acetonitrile solution.

A titration calorimetry technique is used to determine the hydride affinities of 15 polarized dienes, the corresponding five isolated dienes, and the corresponding five conjugated dienes in acetonitrile solution. The experimental results offer insight into the origin of the high chemical potencies of the allenes, the choice of suitable hydride reducing agents to reduce the dienes, and the analyses on the reduction mechanisms.

The first series of experimentally determined Y-N[O.sub.2] (Y = N, O) heterolytic and homolytic bond energy scales for three representative families of synthetic or biochemical significance is reported. The study results would help chemist and biochemists to understand the thermodynamics of N[O.sub.2]/N[O.sub.2.sup.-] release, capture, and transfer.

A study examines the hydride affinities of 80 important p- and o-quinones in dimethyl sulfoxide (DMSO) solution in order to develop the hydride affinity scale of various quinones. Results show that the hydride affinity scale is quite large, indicating that the 80 quinones can form a large and useful library of organic oxidants to provide various organic hydride acceptors for chemists to choose.

The kinetics, thermodynamics, and the reaction intermediate are studied for the reaction of NADH analogue 1-(p-substituted benzyl)-1,4-dihydronicotinamide (G-BNAH) with the radical cation of N-benzylphenothiazine (PT[Z.sup.+]) in acetonitrile. A significant negative kinetic temperature effect is observed on the hydride transfer from BNAH to PT[z.sup.+].

Research has been conducted on polysiloxane-supported NAD(P)H model 1-benzyl-1,4-dihydronicotinamide. The authors report that this model has been designed and synthesized, and that under mild conditions it can reduce activated olefins.

Research has been conducted on the kinetic isotope effect in the one-electron-transfer process from 1-benzyl-1,4-dihydronicotinamide to 9-fluorenylidenemalononitrile. Results indicate that the reaction has proceeded via hydride transfer mechanism.

The authors discuss the mechanism of Hantzsch esters aromatization under thermal conditions. Results demonstrate that the hydrogen atom at the 4 positions has been transferred earlier than at the 1 position.

The effects of substituents on the temperature dependences of kinetic isotope effect (KIE) for the reactions of the hydride transfer from the substituted 5-methyl-6-phenyl-5,6-dihydrophenanthridine (G-PDH) to thioxanthylium (TX+) in acetonitrile were examined, and the results show that the temperature dependences of KIE for the hydride transfer reactions can be converted by adjusting the nature of the substituents in the molecule of the hydride donor. In general, electron-withdrawing groups can make the KIE to have normal temperature dependence, but electron-donating groups can make the KIE to have abnormal temperature dependence. Thermodynamic analysis on the possible pathways of the hydride transfer from G-PDH to TX+ in acetonitrile suggests that the transfers of the hydride anion in the reactions are all carried out by the concerted one-step mechanism whether the substituent is an electron-withdrawing group or an electron-donating group. But the examination of Hammett-type free energy analysis on the hydride transfer reactions supports that the concerted one-step hydride transfer is not due to an elementary chemical reaction. The experimental values of KIE at different temperatures for the hydride transfer reactions were modeled by using a kinetic equation formed according to a multistage mechanism of the hydride transfer including a returnable charge-transfer complex as the reaction intermediate; the real mechanism of the hydride transfer and the root that why the temperature dependences of KIE can be converted as the nature of the substituents are changed were discovered. [ABSTRACT FROM AUTHOR]

The one-electron oxidation potentials [EoxNHE(H2Q)], pKa (pKa1 and pKa2) values, and bond dissociation energies (BDE1 and BDE2) of 118 important p- and o-dihydroquinones in DMSO were systematically predicted for the first time by using DFT method and the PCM cluster continuum model. The calculated results agree well with the available experimental determinations. The study shows that all the five thermodynamic parameters correlate well with the Hammett substituent parameters σp (for p-H2Q, EoxNHE(H2Q·+/H2Q) = 1.66Σσp + 0.54, pKa1 = -5.69Σσp + 16.54, pKa2 = -5.19Σσp + 23.91, BDE1 = 3.43Σσp + 82.29, BDE2 = 4.64Σσp + 67.70 and for o-H2Q, EoxNHE(H2Q·+/H2Q) = 1.85Σσp + 0.46, pKa1 = -5.53Σσp + 13.28, pKa2 = -5.24Σσp + 26.70, BDE1 = 3.54Σσp + 82.08, BDE2 = 3.82Σσp + 75.93), which hints that we can get these thermodynamic parameters as long as the structure of the hydroquinones were known. The comparisons of the calculated five thermodynamic parameters between p-hydroquinones and o-hydroquinones and the number of the phenyl ring effects on these thermodynamic parameters were also studied. At last, intramolecular hydrogen bond energies in hydroquinones at neutral, radical cation, radical, anion different state were systematically calculated and analyzed. Combined with the papers published in our group before, we will have a systematic thermodynamic picture of the transfer details between different kinds of quinones and corresponding hydroquinones, which strongly promote the fast development of the understanding and applications of quinones. [ABSTRACT FROM AUTHOR]

The one-electron reduction potentials of 116 important p-and o-quinones in DMSO and CH3CN were predicted for the first time by using the B3LYP/DZP++ method and the PCM cluster continuum model. The calculated gas-phase electron affinities and one-electron reduction potentials agree well with the available experimental observations, respectively. The study showed the one-electron reduction poten- tials of the 116 quinones range from -0.949 to 1.128 V in DMSO and from -0.904 to 0.971 V in CH3CN. The one-electron reduction potentials of p-quinones tire generally smaller than those of the o-quinones by about 0.132 V. Forquinones with aromaticproperties. 2-substituted-I .4-naphthquinones have the largest one-electron reduction potentials, followed by substituted-I .4-anthraquinones and then by substituted- 9,10-anthraquinones. The study also showed that the one-electron reduction potentials of quinones in DMSO are linearly dependent on the sum of the Hammett substituent parameters σp: ENHE(p-Q/p-Q*) 0.45Σσp. - 0.194(V) and ENHE(o-Q/o-Q*-) 0.45Σσp, - 0.059(V). Combined with the hydride affinities of quinones in the former paper [ΔGH-A(p-Q) = - I6.0Σσp - 70.5 (kcal/mol) and ΔGH-A(p-Q) = - l6.2Σσp - 81.5 (kcal/mol)] and the one-electron reduction potentials of quinones estimated in this work, we obtained the homolytic bond dissociation energies of the hydroquinone anions (QH-) and found that these thermodynamic parameters also have linear correlations against the sum of the Hammett substituent parameters σp, if only the substituents have no larger electrostatic inductive force and no large steric hindrance: BDE(o-QH) = 5.05Σσp + 63.18 (kcal/niol) and BDE(p-QH)-= 5.33Σσp + 71.30 (kcal/mol). Knowledge about the redox potentials of the quinones should be of great value for the understanding of the nature of chemical reactions of quinones. the designing of new electronic materials of quinones. and the examining of biological activities of quinones. [ABSTRACT FROM AUTHOR]

The first heterolytic and homolytic N(O)-NO2 bond dissociation energy scales of three types Y-nitro (Y = N, O) compounds and corresponding radical anions in acetonitrile were established by using titration calorimetry combined with relevant electrochemical data through proper thermodynamic cycles. [ABSTRACT FROM AUTHOR]

The interaction of aryloxychlorocarbenes with dialkyl acetylenedicarboxylates has been examined. Thermolyses of 3-aryloxy-3-chlorodiazirines in the presence of acetylenedicarboxylate resulted in the formation of unexpected polyfunctional 1,3-butadienes and 8-oxatricyclo[3.2.1.02.4]oct-6-enes or of 2-aryoxycarbonylmaleates dependent upon reaction conditions. This work confirmed the nucleophilicity of aryloxychlorocarbenes and underlined their synthetic potential. [ABSTRACT FROM AUTHOR]

Presents the thermodynamic evaluation of the mechanisms involved in nitric oxide-initiated reactions with 3,6-dibromocarbazolide anion and related carbanion. Role of nitric oxide in the reaction; Reaction of nitric oxide with nitration; Determination of heterolytic and homolytic dissociation energies of the nitrogen-nitric oxide bonds.

Construction of pyrrolidinyl-spiroindoles with easily available starting materials has attracted considerable attention from the synthesis community and is in great demand. Here, we describe a base-promoted formal (3 + 2) cycloaddition of α-halohydroxamates with alkenyl-iminoindolines. The present methodology features mild reaction conditions and a broad substrate scope with up to 99% yield and excellent diastereoselectivity. The versatility of this approach is demonstrated through valuable synthetic transformations. Preliminary mechanistic studies shed light on the mechanism of this cycloaddition process.

An N -heterocyclic carbene organocatalytic 1,4-difunctionalization of 1,3-enynes was developed. This organocatalytic strategy was suitable for a broad spectrum of substrates to efficiently synthesize allenic ketones bearing diverse substituents. Preliminary mechanistic studies suggest a radical reaction pathway for this organocatalytic acylalkylation process.