Synthesis and mesomorphic properties of 4-(4-bromopropyloxy)-4’-(4-alkyloxybenzylidene)anilines

This article describes the preparation and liquid crystalline properties of a new homologous series of 4-（4-bromopropyloxy）-4’- （4-alkyloxybenzylidene）anilines in which the phenyl ring is armed by a bromopropyloxy chain.The thermal behavior and mesomorphic properties of the synthesized compounds were studied with particular attention given to the correlation between their phase transition temperatures and anisotropic change influenced by molecular structure.All the members displayed enantiotropic smectic phase except for the homologue with the longest alkyloxy chain(R = C₁₈H₃₇),exhibiting only monotropic characteristic. The presence of bromine atom from the propyloxy side chain is found to be capable of altering and influencing the mesomorphic properties.     

（Salen）Ti（Ⅳ）-Catalyzed Asymmetric Ring-opening of meso Epoxides Using Dithiophosphorus Acid as the Nucleophile

The asymmetric ring-opening of epoxides with dithiophosphorus acids catalyzed by a （salen）Ti（Ⅳ） complex formed in situ from the reaction of Ti（OPr-i）4 and the chiral Schiff base derived from （1R,2R）-（＋）-diaminocyclohexane was realized. The resulting products were obtained with low to good enantioselectivity （up to 73% ee）.     

Studies on the Oxazaborolidine-catalyzed Enantioselective Reduction of 3-Morpholin-4-yl-1-phenyl-1-propanone with Density Functional Theory

Density functional theory (DFT) has been applied to study the enantioselective reduction of 3-morpholin-4-yl-l-phenyl-l-propanone with borane catalyzed by (S)-4-benzyl-5,5-diphenyl-l,3,2-oxazaborolidine at the B3LYP/6-31G* level. All molecular species involved in the four reaction steps have been fully optimized and the structural parameters are provided, and the micro process of reaction was also investigated. The catalyst-alkoxyborane adduct formed in step Ⅲ exhibits a B-O-B-N tetra-atomic ring. Reaction coordination calculations show that BH3 can react with 3-morpholin-4-yl-l-phenyl-l-propanone spontaneously, resulting in the need of 2 tool BH3 in the reaction.     

Theoretical insight into phosphoric acid-catalyzed asymmetric conjugate addition of indolizines to a,β-unsaturated ketones

Phosphoric acid catalysis is a powerful tool for the construction of new CààC bonds because of its unique LUMO-lowering activity. Theoretical calculations were employed to investigate phosphoric acidcatalyzed asymmetric conjugate addition of indolizines to a,b-unsaturated ketones. The calculation results showed that this transformation proceeds via a reaction pathway involving nucleophilic addition,deprotonation–aromatization, and tautomerization. The computational results showed that deprotonation–aromatization is the rate-determining step and the enantioselectivity-determining step.The S-configured product was preferentially generated via a pathway starting from the s-cis conjugated ketone, whereas the s-trans isomer led to a side product with the R configuration. Non-covalent interaction analysis showed that the enantioselectivity is mainly caused by bond-rotation strain in the transition states of the deprotonation–aromatization step.     

Theoretical Studies on the N-Phenylpyrrolidine Formation Mechanism Based on the Reaction of Phenylamine with 1,4-Butanediol

The reaction mechanism of phenylamine reacting with 1,4-butanediol to give N- phenylpyrrolidine was investigated with traditional transition state theory. Based on the experimental results, two reaction channels were discussed. The geometries of their reactants, products, intermediates and transition states were optimized. The possible transition State and activation energy were determined by vibrational analysis and IRC verification. And finally, the main reaction channel was given.     

A DFT Study of Thiophene Adsorption on the Rh（111） Surfaces

Thiophene adsorption on the Rh(111) surfaces has been investigated by density functional theory.The results show that the adsorption at the hollow and bridge sites is the most stable.The molecular plane of the thiophene ring is distorted,the C=C bond is stretched to 1.448  and the C-C bond is shortened to 1.390.The C-H bonds tilt 22～42oaway from the surface.The calculated adsorption geometries are in reasonable agreement with population analysis and density of states.The thiophene molecule obtains 0.74 electrons,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.The reaction paths and transition states for desulfurization of the molecule have been investigated.The bridge adsorption structure of thiophene leads to a thiol via an activated reaction with an energetic barrier of 0.30 eV.This second step is slightly difficult,and dissociation into a C4H4 fragment and a sulfur atom is possible,with an energetic barrier of 0.40 eV.     

The Application of Suzuki Coupling Reaction on the Preparation of Carbosilane Dendrimers with 4-（Naphthalen-l-yl）phenyl Core

Carbosilane dendrimers with p-bromophenyl core were synthesized by alternating Grignard and hydrosilylation reaction. And the α-naphthalenyl was connected to the core by the Suzuki coupling reaction. A new carbosilane dendrimer with big π-conjugated structure [4-（naphthalen-l-yl）phenyl core] was given. It shows Suzuki coupling reaction is an effective and powerful core-functionalization method and the satisfactory result can be obtained through prolonging the reaction time with the increase of the generation of dendrimer.     

Ab initio Study on the Tautomerization Mechanism and the Kinetics of Formamide

The tautomerism of formamide has been investigated by ab initio calculation using RHF/4-31G basis set. The change in some physical properties along the reaction path is presented. In the study of molecular reaction kinetics, we have calculated all the kinetic parameters according to statistical thermodynamics and transition state theory. The combination of kinetics analysis with IRC analysis has indicated that the tautomerism is concerted but the geometric changes are nonsynchronous; the lifetime of the transition state is short and the transition state is tight type; the formamide is more stable than formimidic acid; the kinetic rate constant of backward reaction is larger than that of the forward reaction in the range of temperature studied.     

Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of Hydrogen

The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.     

Ab Initio Study of the Dehydrogcnation of Methylenimine

The ab initio calculations were performed by the intrinsic reaction coordinated(IRC) method for the reaction paths of the dehydrogenations of methylenimine. We determined the geometries and energies of the transition states and obtained the activation energies, activation entropies and the statistical A factors on the RHF/4 -31G singlet potential energy surface. The mode selective study reveals the intrinsic reaction coordi-nates(URC) of 1 ,1 and 1 ,2 dehydrogenations of methylenimine to be related with the H2C= group symmetrical stretch mode and the =NH group stretch mode, respectively. The vibration coupling between the normal coordinates occurs in either of these two reaction paths.     

Synthesis of a Novel Diamine 4-[（4＇-Butoxyphenoxy）carbonyl]- phenyl-3＂, 5＂-diaminobenzoate and Corresponding Polyimides

A novel diamine 4-[（4＇-butoxyphenoxy）carbonyl]phenyl-3＂,5＂-diaminobenzoate （BCDA） was synthesized from 4-butoxyphenol, 4-hydroxybenzoic acid and 3,5-dinitrobenzoic acid through four main intermediates, and a series of polyimides were also synthesized. All the intermediates and the final product were characterized by FTIR and 1H-NMR. The key step in synthesis route is selective hydrolyzation of two ester groups in 4-butoxyphenyl-4＇-acetoxybenzoate, by adjusting the reaction temperature and the concentration of ammonia, shorteding the reaction time. The properties of the novel polyimides, such as the aggregation structures, glass transition temperature, solubility and the pretilt angles, were carded out.     

Comparative studies on the mechanism of uridine phosphorolysis

We have used quantum mechanical method to study the transition states(TSs) of uridine phosphorolysis reaction. Comparing the four different reaction pathways and the five transition states obtained, we conclude that enzymatic uridine phosphorolysis takes place mainly according to acid-catalyzed SN2 mechanism. The proposed reaction pathway is consistent with many experimental results.     

Theoretical Studies on the Reaction Mechanism of AsCl_3 with H_2 in the Vapor Phase Epitaxy of GaAs

The reaction mechanism of AsCl3 with H2 has been studied by using the method of BHandHLYP in Density Functional Theory (DFT) at the 6-311G** basis set. The transition state of each reaction is verified via the analysis of vibration mode and Intrinsic Reaction Coordinate (IRC). Meanwhile,single-point energy has been calculated at the QCISD(T)/6-311G** level,and the zero-point energy correction has been made to the total energy and reaction energy barrier. It shows that AsCl3 reacts with H2 to first result in AsHCl2 which may incline to self-decompose and finally afford the product As2,or continue to react with H2 to provide the product AsH3. The computing result demonstrates that the former is the main reaction channel.     

Kinetics of the Oxidative Dehydrogenation of Propane over a VMgO Catalyst

The reaction kinetics of the oxidative dehydrogenation of propane was studied at 475-550℃ over a VMgO catalyst. Vanadium-magnesium-oxides are among the most selective and active catalysts for the dehydrogenation of propane to propylene. Selectivity to propylene up to about 60% was obtained at 10% conversion, but the selectivity decreased with increasing conversion. No oxygenates were detected, the only by-products were CO and CO2. The reaction rate of propane was found to be first order in propane and close to zero order in oxygen, which is in agreement with a Mars van Krevelen mechanism with the activation of the hydrocarbon as the rate determining step. The activation energy of the conversion of propane was found to be 122±6 kJ/mol.     

Addition Mechanisms of Phenol toward Formaldehyde under Acidic Condition： a Theoretical Investigation

The reaction mechanisms of phenol with formaldehyde in the first and second addition at the ortho- and para-position in acid solution were theoretically investigated at the PW91/DNP level with solvent effects included. The reaction of phenol with protonated methanediol firstly forms an adduct intermediate, via a SN2 mechanism with a water molecule as the leaving group. From the adduct intermediate, there are two reaction channels involving a proton transfer to form the addition products. One is that a proton directly transfers via a four-membered ring transition state with a notable energy barrier (Four-member mechanism). Another mechanism involving a water molecule as catalyst to mediate the proton transfer (WCP mechanism), is a barrierless process, indicating that the formation of the adduct intermediate, the first reaction step, is rate-limiting. The reaction products are free hydroxymethyl phenols and/or hydroxybenzy carbocation (HOC6H4CH2+) which plays an important role in the following formation of methylene and methylene ether linkages. The second addition reactions between formaldehyde and hydroxymethyl phenol at all possible reaction sites of the phenol ring in acid solution were also investigated and discussed.     

Synthesis of 1-Bromo-3-methoxy-4-propoxy-5-iodobenzene——A Novel Efficient Process for the Synthesis of Brominated Aromatic Compound

The reaction of aromatic carboxylic acid with oxalyl chloride gives rise to the corresponding acid chloride which without purification is treated with the sodium salt of mercaptopyridine oxide in the presence of 2,2-azo-bisisobutyronitrile (AIBN), radical initiator to give a brominated aromatic compound. After etherification and oxidation, 5-iodovaniline was converted to trisubstituted benzene carboxylic acid which give 1-bromo-3-methoxy-4-propoxy-5-iodobenzene by this new brominating process with a yield of 74%.     

Low Temperature Heat Capacities and Thermodynamic Properties of Zinc L-Threonate Zn（C4H7O5）2（s） by Adiabatic Calorimetry

Low-temperature heat capacities of the solid compound Zn（C4H7O5）2（s） were measured in a temperature range from 78 to 374 K, with an automated adiabatic calorimeter. A solid-to-solid phase transition occurred in the temperature range of 295？322 K. The peak temperature, the enthalpy, and entropy of the phase transition were determined to be （316.269±1.039） K, （11.194±0.335） kJ？mol-1, and （35.391±0.654） J？K-1？mol-1, respectively. The experimental values of the molar heat capacities in the temperature regions of 78？295 K and 322？374 K were fitted to two polynomial equations of heat capacities（Cp,m） with reduced temperatures（X） and [X = f（T）], with the help of the least squares method, respectively. The smoothed molar heat capacities and thermodynamic functions of the compound, relative to that of the standard reference temperature 293.15 K, were calculated on the basis of the fitted polynomials and tabulated with an interval of 5 K. In addition, the possible mechanism of thermal decomposition of the compound was inferred by the result of TG-DTG analysis.     

A Study on the Interaction of the DAS-K with Bovine Serum Albumin by On-line Ultrafiltration and Chemiluminescence

Potassium dehydroandrographolide succinate （DAS-K） has antibacterial and antiviral effects. It has been used widely for the treatment of virus pneumonia, malaria and respiratory infections. In this work, a novel flow-injection chemiluminescence （CL） method for the determination of DAS-K was proposed. The method is based on the reaction between DAS-K and hexacyanoferrate（III） in alkaline solution to give weak CL signal, which is enhanced by rhodamine B. The experimental conditions for the CL reaction were optimized and the possible reaction mechanism was discussed. Under the optimum conditions, the concentration of DAS-K is proportional to the CL intensity in the range of 0.1-80 μmol·L^-1 with a detection limit of 0.05 μmol·L^-1. The interaction of the DAS-K with bovine serum albumin by on-line ultrafiltration and flow-injection chemiluminescence was studied. The concentrations of unbound DAS-K from ultra filter tube were determined by the flow-injection CL method. The binding parameters were estimated by the Scatchard plot and Klotz plot. The proposed system proved that FIA-CL coupled with on-line ultrafiltration sampling was a fast and simple technique for the study of drug-protein interaction.     

Competition between C-C and C-H Activation in Reactions of Neutral Nickel Atom with Cycloalkanes （n = 3-7）

A theoretical investigation of the reaction mechanisms for C-H and C-C bond activation processes in the reaction of Ni with cycloalkanes C,,H2. （n = 3-7） is carried out. For the Ni ＋ CnH2, （n = 3, 4） reactions, the major and minor reaction channels involve C-C and C-H bond activations, respectively, whereas Ni atom prefers the attacking of C-H bond over the C-C bond in CnH2n （n = 5=7）. The results are in good agreement with the experimental study. In all cases, intermediates and transition states along the reaction paths of interest are characterized, It is found that both the C-H and C-C bond activation processes are proposed to proceed in a one-step manner via one transition state. The overall C-H and C-C bond activation processes are exothermic and involve low energy barriers, thus transition metal atom Ni is a good mediator for the activity of cycloalkanes CnH2n （n = 3 -7）.     

Palladium-catalyzed hydrosilylation of ynones to access silicon-stereogenic silylenones by stereospecific aromatic interaction-assisted Si–H activation

Hydrosilylation is one of the most important reactions in synthetic chemistry and ranks as a fundamental method to access organosilicon compounds in industrial and academic processes. However, the enantioselective construction of chiral-at-silicon compounds via catalytic asymmetric hydrosilylation remained limited and difficult. Here we report a highly enantioselective hydrosilylation of ynones, a type of carbonyl-activated alkynes, using a palladium catalyst with a chiral binaphthyl phosphoramidite ligand. The stereospecific hydrosilylation of ynones affords a series of silicon-stereogenic silylenones with up to 94% yield, 20:1 regioselectivity and 98:2 enantioselectivity. The density functional theory(DFT) calculations were conducted to elucidate the reaction mechanism and origin of high degree of stereoselectivity, in which the powerful potential of aromatic interaction in this reaction is highlighted by the multiple C–H-π interaction and aromatic cavity-oriented enantioselectivitydetermining step during desymmetric functionalization of Si–H bond.