Ab initio study of the reaction path of the reaction HNCO+CN

HNCO is a convenient photolytic source of NCO and NH radicals for laboratory kinetics studies of elementary reaction[1] and plays an important role in the combustion and atmosphere chemistry. It can re- move deleterious compounds rapidly from exhausted ga…     

Ethyl α-cyanoacrylate in the Michael reaction

Ethyl -cyanocarylate undergoes the Michael reaction with strong CH-acids (pK _a < 13) in the presence of strong basic amines such as butylamine, piperidine, and triethylamine. Only polymerization of ethyl -cyanoacrylate occurs under the same conditions with weaker CH-acids in the presence of less basic amines such as aniline, N-methylaniline, and pyridine.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2449–2452, October, 1992.     

Combination of the Claisen-Schmidt reaction,the Michael addition,and the Hantzsch reaction in the synthesis of 2,6′-bis-aryl-3,4′-bipyridines

Russian Chemical Bulletin - Pyridine-3-carbaldehyde reacted with 1-(aryl)ethan-1-ones to give 1,5-diaryl-3-(pyridin-3-yl)pentane-1,5-diones, which were further converted to...     

Synthesis of the integrastatin nucleus using the Ramberg-Bäcklund reaction

[reaction: see text] The first synthesis of the tetracyclic nucleus of the Integrastatins, natural products that have been shown to selectively inhibit HIV-1 integrase, is reported. Key steps of this synthesis involve a novel cis-selective Ramberg-B?cklund reaction and an unusual Lewis acid-promoted cyclization step.     

Preparation of natural isovaleraldehyde by the Maillard reaction

Isovaleraldehyde possesses malty,fruity,cocoa-like odor and is widely used in fruit,chocolate,coffee flavors.The preparation of natural isovaleraldehyde by the Maillard model reaction was studied in this paper.The effects of the ratio of D-glucose/L-leucine, reaction temperature and pH value on the yield of isovaleraldehyde were explored.The optimum conditions were as follows: n(D-glucose):n(L-leucine)=4,temperature 150℃,reaction time 3 h,pH 5.The highest yield of isovaleraldehyde obtained was about 32%.     

Studies on the cyclization reaction of D-aspartic acid

The cyclization reaction of D-aspartic acid was studied, the carboxyl groups of D-aspartic acid were protected by benzyl alcohol to give compound D-dibenzyl aspartate. Then (4R)-benzyl azetidine-2-one-4-carboxylate and meso-3,6-disubstituted piperazine- 2,5-diones were synthesized via intramolecular cyclization and intermolecular cyclization of D-dibenzyl aspartate, respectively, and their structures were confirmed by 1H NMR and MS. Both cyclization reaction conditions were also investigated in detail.     

Systematic study for the stereochemistry of the Atherton–Todd reaction

Under the Atherton–Todd reaction conditions, the stereochemistry on the reaction of H-phosphinates with different nucleophiles (e.g., amines, alcohols, phenols) was investigated. All reactions took place stereospecifically with inversion of configurations at the phosphorus centers. The reaction might proceed via a phosphoryl chloride intermediate with retention of configuration at phosphorus, followed by the attack of nucleophiles from the backside of Cl to give the substitution products with inversion of configuration at the phosphorus center. A plausible mechanism was proposed for these reactions.     

Can the nitroso ene reaction proceed concertedly?

All nitroso ene reactions so far reported follow exclusively stepwise reaction paths. Herein, we report the first concerted nitroso ene reaction that occurs between o-isotoluene (or its naphthalenic analogues) and nitroso compounds (e.g., nitrosomethane and 4-nitronitrosobenzene). [reaction: see text]     

Computer investigations on the asymptotic behavior of the rate coefficient for the annihilation reaction A + A → product and the trapping reaction in three dimensions

We have performed intensive computer simulations of the irreversible annihilation reaction: A + A → C + C and of the trapping reaction: A + B → C + B for a variety of three-dimensional fluids composed of identical spherical particles. We have found a significant difference in the asymptotic behavior of the rate coefficients for these reactions. Both the rate coefficients converge to the same value with time t going to infinity but the convergence rate is different: the O(t(-1/2)) term for the annihilation reaction is higher than the corresponding term for the trapping reaction. The simulation results suggest that ratio of the terms is a universal quantity with the value equal to 2 or slightly above. A model for the annihilation reaction based on the superposition approximation predicts the difference in the O(t(-1/2)) terms, but overestimates the value for the annihilation reaction by about 30%. We have also performed simulations for the dimerization process: A + A → E, where E stands for a dimer. The dimerization decreases the reaction rate due to the decrease in the diffusion constant for A. The effect is successfully predicted by a simple model.     

Analysis of the Volmer–Krishtalic mechanism for the chlorine electrode reaction

The dependencies of the current density and surface coverage of the adsorbed intermediates on overpotential were established without kinetic approximations for the chlorine electrode reaction under the Volmer–Krishtalic mechanism. Tafelian regions were obtained which slope values cannot be derived from the use of the rate determining step criteria, such as 2.3026(2RT/3F) and 2.3026(RT/F), as well as two or three Tafel regions with different slopes in the same anodic or cathodic curve. The existence of limiting kinetic current densities was also demonstrated. Finally, the results obtained were analysed and discussed, comparing them with those obtained by the usual methods.     

Adapted numerical modelling of the Belousov–Zhabotinsky reaction

Adapted numerical schemes for the integration of differential equations generating periodic wavefronts have reported benefits in terms of accuracy and stability. This work is focused on differential equations modelling chemical phenomena which are characterized by an oscillatory dynamics. The adaptation is carried out through the exponential fitting technique, which is specially suitable to follow the apriori known qualitative behavior of the solution. In particular, we have merged this strategy with the information coming from existing theoretical studies and especially the observation of time series. Numerical tests will be provided to show the effectiveness of this problem-oriented approach.     

Synthesis of β-substituted tetrahydrofurans by the prins reaction

Mixtures of 3-trif uoroacetoxy- and 3-chloro-4-alkyltetraliydrofurans were synthesized by the reaction of a series of-olefins with formaldehyde in trifuoroacetic acid and trimethylchlorosilane.The characteristics of the mixtures of cis and trans isomers are given, and the n_D ²⁰ values are given for the trans isomers.Bashkir State University, Institute of Fine Organic Synthesis. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 605–608, May, 1995. Original article submitted November 4, 1994; revision submitted May 10, 1995.     

Brønsted guanidine acid-base ionic liquids: novel reaction media for the palladium-catalyzed Heck reaction

[reaction: see text]. Br?nsted acid-base ionic liquids (GILs) based on guanidine and acetic acid are efficient reaction media for palladium-catalyzed Heck reactions. They offer the advantages of high activity and reusability. GIL2 plays multiple roles in the reaction: it could act as solvent, as a strong base to facilitate beta-hydride elimination, and as a ligand to stabilize activated Pd species.     

Explicit definition of the reaction coordinate for the Jackels–Gu–Truhlar projection technique to compute harmonic vibrational frequencies along the intrinsic reaction path

It is shown that the Jackels–Gu–Truhlar projection technique for computing harmonic frequencies along the intrinsic reaction path is equivalent to use of a new, enormously broad family of the so-called hyperplanar-vibrational-surface (HVS) reaction coordinates, namely, for any arbitrarily chosen set of internal variables , the appropriate HVS reaction coordinate, s, is implicitly defined via the requirement that it remains constant on any so-called orthogonal-to-path hyperplane in the coordinate space spanned by variables . It is proven that s defined in such a way satisfies the local Hofacker–Marcus conditions and therefore there is no linear term in a Taylor expansion of the potential in terms of vibrational coordinates Q. Since the transformation from Q and s to is explicitly defined, one can use a standard technique to account for potential anharmonicities along the reaction path.     

Revisiting the Corey-Chaykovsky reaction: the solvent effect and the formation of β-hydroxy methylthioethers

The classical Corey-Chaykovsky (CC) reaction of ketones in ethereal solvents (i.e., THF or Et₂O) resulted in the production of a significant amount of β-hydroxy methylthioether 2 along with normal epoxide product 1. Some interesting and synthetically useful transformations of the CC reaction product of cyclopropyl ketones were also described.     

Calculation of the quantum yield of the photochemical isomerization reaction → methoxybutadiene methoxycyclobutene

The methoxybutadiene → methoxycyclobutene photoisomerization process was simulated and the quantum yield of the product was calculated. The validity of the theoretical ideas and model concepts used in the proposed method for the calculation of quantum yields of photochemical reactions was confirmed. It was shown that the empirical parameter used in the model (broadening parameter) is stable in value and has the inherent property of transferability over a series of related molecules and analogous reactions. The cause of a substantial difference between the experimental quantum yields of reactions of the same type for a number of molecules bearing different substituents was revealed: this is a change in the form of vibrations and/or in the magnitude of structural rearrangement that directly involves the substituent.     

Theoretical studies on the reaction path and dynamics of the reaction CH_3+H_2O→CH_4+OH

The reaction path, the dynamical properties along the reaction path and CVT rate constants are computed by the ab initio MO method, the reaction path Hamiltonian theory and the variational transition state theory. The results show that the effect of the electron correlation energy on activation barrier is large, the recrossing and tunneling effects exist in the reaction.     

Density functional theory study of the cycloaddition reaction of furan derivatives with masked o-benzoquinones. Does the furan act as a dienophile in the cycloaddition reaction?

The molecular mechanism for the cycloaddition reaction between 2-methylfuran and a masked o-benzoquinone has been characterized using quantum mechanical calculations at the B3LYP/6-31G theory level. An analysis of the results on the reaction pathway shows that the reaction takes place along a polar stepwise mechanism. The first and rate-determining step corresponds to the nucleophilic attack of the furan ring on the doubly conjugated position of the 2,4-dienone system present at the masked o-benzoquinone to give a zwitterionic intermediate. Closure of this intermediate affords the formally [2 + 4] cycloadduct. For the second step two reactive channels have been characterized corresponding to the formation of the formally [2 + 4] and [4 + 2] cycloadducts. Analysis of the energetic results indicates that while the first is the meta regiocontrolling and endo stereocontrolling step, the second one is responsible for the formation of the unexpected formally [2 + 4] cycloadduct. The global and local electrophilicity/nucleophilicity power of the reactants and intermediate have been evaluated to rationalize these results. Density functional theory analysis for these cycloadditions is in complete agreement with the experimental outcome, explaining the reactivity and selectivity of the formation of the formally [2 + 4] cycloadducts.     

Radical cyclisation studies of β-nitroamines from the nitro-Mannich reaction

A range of novel β-nitroacetamides with an alkenyl- or alkynyl tether were synthesized using the deprotonative or conjugate addition nitro-Mannich reaction. They were subjected to radical denitration-cyclisation with a 10 equivalent excess of tributyltin hydride, catalytic AIBN in refluxing benzene to explore the structural and electronic requirements for efficient cyclisation. Cyclisations of the β-nitroacetamides were successful in most cases, undergoing 5-exo-trig cyclisation to give the desired cyclopentyl or indanyl structures. Radical 1,4-translocation of a phenyl group was observed in several cases. Diastereoselectivity was low, with 2 or 3 of 4 possible diastereoisomers observed in most cases. Further purification by crystallisation allowed the isolation of some as single diastereoisomers. It was found that higher yields were obtained by increasing the substitution or reducing the degrees of freedom of the tether between the nitro group and the radical acceptor.     

Modelling of the NO + CO reaction over inhomogeneous surfaces

A phenomenological model of \(\mathrm {CO}\) oxidation with \(\mathrm {NO}\) reaction proceeding over composite (supported) catalysts is proposed and solved numerically using the finite difference method. The model is based on the coupled system of PDEs subject to nonclassical conjugate conditions at the catalyst-support interface and includes: the bulk diffusion of reactants from a bounded vessel towards the catalyst surface and the bulk one of the reaction products from the surface into the same vessel, adsorption and desorption of particles of reactants, and surface diffusion of adsorbed molecules. The readsorption of the reaction product N\(_2\)O is also taken into account. The influence of the rate constants of the adsorbed particle jumping via the catalyst-support interface and reaction rate constants on the surface reactivity is investigated. It is shown that the turnover rates of the CO and NO into products N\(_2\)O, CO\(_2\), and N\(_2\) are nonmonotonic time functions and depending on values of the kinetic parameters may possess one or two maxima. The N\(_2\)O readsorption in case of the existence of two maxima essentially increases the turnover rates and extends the duration of their high values. The mechanism and conditions for arising of the second maximum is discussed. It is also shown that the variation of the particle jumping rate constants influences differently the size of the jump discontinuity of concentrations of different adsorbates at the catalyst-support interface.