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.     

A collinear tandem time-of-flight mass spectrometer for infrared photodissociation spectroscopy of mass-selected ions

An apparatus based on collinear tandem time-of-flight mass spectrometer has been designed for the measurement of infrared photodissociation spectroscopy of mass-selected ions in the gas phase.The ions from a pulsed laser vaporization supersonic ion source are skimmed and mass separated by a Wiley-McLaren time-of-flight mass spectrometer.The ion of interest is mass selected,decelerated and dissociated by a tunable IR laser.The fragment and parent ions are reaccelerated and mass analyzed by the second time-of-flight mass spectrometer.A simple new assembly integrated with mass gate,deceleration and reacceleration ion optics was designed,which allows us to measure the infrared spectra of mass selected ions with high sensitivity and easy timing synchronization.     

Research on the Synthesis and Optical Properties of Isomeric Bichromophoric Compounds --3-or 4- Phenyl 7-Coumarin ω-9-Anthracene-Poly-methene Carboxylate

Six bichromophoric compounds-substituted coumarin ω -9-anthra-cene-poly-methene carboxylate and five model compounds were synthesized. Among them, eight compounds are new ones. Intramolecular singlet energy transfer has been demonstrated in the bichromophoric compounds 1? and studied in some detail. The absorption spectra of the compounds 1-6 bear evidence that the π-electron systems of coumarin and anthracene ring do not overlap appreciably. The coumarin moiety of the bichromophoric compounds molecule was excited at 314nm and the resulting fluorescence was characteristic of the anthracene group. The efficiency of transfer of singlet excitation from coumarin moiety to the anthracene grou is about 100% in both calculation and observation and the rate of the singlet energy transfer is about 1014 sec in the compounds 4-6. A possible mechanism of intramolecular energy transfer was suggested. The difference between 4-phenyl compounds 1-3 and 3-phenyl compounds 4-6 in spectra was com -pared.     

Theoretical study on tetrazole and its derivatives (3) MP2 and thermodynamic calculations of amino derivatives of tetrazole

Fully optimized geometries and electronic structures of amino derivatives of tetrazole are obtained at MP2/6-31G* level. The tetrazole rings are planar and aromatic for all the amino derivatives of tetrazole. The amino group is not co-planar with the ring and its conformation is mainly determined by the lone pair electronic repulsion between the substituent and the ring. N(4) atom is more negatively charged and is the most probable coordination site. The energy gaps between LUMOs and HOMOs of 2H-aminotetrazoles and C-aminotetrazole neutrals are smaller than those of the corresponding 1H-isomers and N-aminotetrazole neutrals respectively. The IR frequencies, thermodynamic properties and temperature-dependent functions for heat capacities in the form (a bT cT2) in the 300-1000K range are reported.     

DSC study of phase transition of anhydrous phospholipid DHPC and influence of water content

The phase transition behavior of 1,2-di-n-heptadecanoyl phosphatidylcholme (DHPC)with and without water has been studied by use of differential scanning calorimetry It was found by experiment that the glass transition occurred at first during the first heating of a sample of DHPC without water and then the sample underwent melting as an ordinary crystal.Therefore the sample of DHPC without water was a glassy crystal However,the DHPC sample crystallizing from melt was an ordinary crystal From the relationship between the total melting enthalpy Qf of freezable water and the water content h,it was concluded that the water contained in the DHPC samples might exist in three states recognizable thermodynamically.The water in the first state was an unfreezable water It was the water bound directly with the head groups of the phospholipid,i.e.the primary hydration water Every head group might bind seven such molecules of water.The water in the second state was the secondary hydration water,us melt ing point was     

Excited-state properties of asymmetric pentaazadentate expanded porphyrins

The research results of the excited-state properties of asymmetric pentaazadentate ex-panded-porphyrins are reported. The results show that the emission spectra appear in the 770-820 nm region in accord with the different substituents on the benzene ring. The quantum yield of fluorescence is less than 0.02, and the lifetime of the first singlet excited state (S1) is shorter than 1ns. There are excellent linear relationships between the energy of the S1 and the Hammett constants as well as the quantum yield of fluorescence and the electrophilic substituent constants σ+. The energies of the lowest excited triplet state (T1) of the complexes are in the range of 94 -130kJ/mol. The lifetime of T 1 is as long as tens of microseconds. The T1-Tn transient absorption spectra appear in 450-550 nm region. And the quantum yield of title compounds for generating singlet oxygen is as high as 0.9.     

On the Construction of n-Electron States with Symplectic Symmetry

Under quasispin scheme, a complete group theoretical classification of fermion states with symplectlc symmetry is proposed. Furthermore, the first and second order irreducible tensor operators are investigated in detail to approach the fermion states with explicit forms.     

Effects of Aluminum on Thermal Decomposition of Hexogen/Ammonium Perchlorate

Thermogravimetry-differential scanning calorimetry-mass spectrometry-Fourier transform infrared spectrometry（TG-DSC-MS-FTIR） simultaneous analysis was used to study the effects of 10.7 μm and 40 nm Al on the thermal decomposition of the Hexogen/ammonium perchlorate（RDX/AP,1/2,mass ratio） mixture.TG-DSC results show that there are two mass loss processes for the thermal decomposition of RDX/AP/Al.The first one is mainly ascribed to the thermal decomposition of RDX.The reaction rate of RDX/AP/10.7 μm Al is so fast that the apparent activation energy,calculated by model-free Friedman method,is negative,which is the same as that of RDX/AP.30％（mass fraction） 40 nm Al added in RDX/AP change the activation energy from negative to positive value.The second mass loss process of the RDX/AP/A1 mixture is ascribed to the thermal decomposition of AP.This process can be divided into three stages for RDX/AP with and without Al.The kinetics model is not changed in the presence of micro-sized Al,while it is changed from CnB/D1/D1 to CnB/D1/D4 after the addition of 40 nm Al to RDX/AP.The reaction rate constant of the first stage and the end temperature of the second stage decrease,while the end temperatures of the third stage increase in the presence of 40 nm Al.The MS-FTIR results show there is a competition between the formation reactions of HNCO,N2O and NO2 during the second mass loss process.     

Synthesis, Structure and Biological Activities of Novel Triazole Compounds Containing N,N-Dialkyldithiocarbamate Moiety

Introduction As an important type of fungicides, triazole compounds are highly efficient, low poisonous and inward absorbent.1-3 At present, the studies on triazole derivatives are mainly concentrated on compounds with triazole as the only active group. The report of triazole compounds that contain both triazole group and other active group in a single molecule has rarely been found. Dialkyl-substituted dithiocarbamate salts have also shown interesting biological effects.4 N,N-Dialkyldithio-…     

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.     

The scaling behavior of the second virial coefficient of linear and ring polymer

The scaling behavior of the second virial coefficient of ring polymers at the theta temperature of the corresponding linear polymer(θ_L) is investigated by off-lattice Monte Carlo simulations. The effects of the solvents are modeled by pairwise interaction between polymer monomers in this approach. Using the umbrella sampling, we calculate the effective potential U(r) between two ring polymers as well as the second virial coefficient A_2 of ring polymers at θ_L, which results from a combination of 3-body interactions and topological constraints. The trend in the strength of the effective potential with respect to chain length shows a non-monotonic behavior, differently from that caused only by topological constraints. Our simulation suggests that there are three regimes about the scaling behavior of A_2 of ring polymers at θ_L: 3-body interactions dominating regime, the crossover regime, and the topological constraints dominating regime.     

STRUCTURAL RULES OF TRANSITIONMETAL CARBONYL COMPOUNDS

In this article we have proposed two topological rules to account for the electronic structures of transition-metal carbonyl compounds. The second rule is applied to those which have polyhedral metalhc skeletons with triangular faces and their derivates, while the first rule is applied to all the others We have used these two rules to analyze 261 structure-known compounds with the number of metal atoms from 2 to 12, and the results show that the two rules are in good agreement with the experimental facts. Furthermore, we have also derived from the second rule a formula which can be used to account for the electronic structures of closedpacking carbonyl compounds and which is the same as that given by Ciani and his coworkers.     

Theoretical study of the separation mechanism of ionizable compounds in capillary electrochromatography

The migration mechanism of ionizable compounds in capillary electrochromatography (CEC) is more complicated than in high performance liquid chromatography (HPLC) due to the involvement of electrophoresis and the second chemical equilibrium. The separation mechanism of ionizable compounds in CEC has been studied theoretically. The electrochromatographic capacity factors of ions (k~*) in CEC and in the pressurized CEC are derived by phenomenologicai approach. The influence of pH, voltage, pressure on k~* is discussed. In addition, the k~* of weak acid and weak base are derived based on acid-base equilibrium and the influence of pH on k~* is studied theoretically.     

Ring Contraction Reaction of 4H-1,3-Oxazin-4-ones under Electrospray Ionization Conditions

Ring contraction reactions of heterocyclic compounds under mass ionization conditions are important and interesting phenomenon.[1] It should be very useful to elucidate the fragmentation of some novel heterocyclic compounds and to identify the structures of some effective compounds in a screened library by mass spectrometric method, which is an easy and available method for identification of effective members in a library due to development of LC-MS. Recently several ring contraction reactions have been reported in literatures.     

Synthesis, Structure and Biological Activities of Novel Triazole Compounds Containing 4,6-Dimethyl-pyrimidin-2-ylthio Group

Introduction As an important type of fungicides, triazole com-pounds are highly efficient, low poisonous and inward absorbent.1-3 At present, the studies on triazole deriva-tives are mainly concentrated on compounds with tria-zole as the only active group. The report on triazole compounds that contain both triazole group and other active group in a single molecule has rarely been found. Some pyrimidines have been used as highly efficient and lowly poisonous fungicides4 in controling powdery mi…     

Polyoxygenated anti-inflammatory biscembranoids from the soft coral Sarcophyton tortuosum and their stereochemistry

Five novel biscembranoids,ximaolides H-L(1-5),along with four known related compounds(6-9) were isolated from the Hainan soft coral Sarcophyton tortuosum.The structures of the new compounds were determined by extensive spectroscopic analysis,quantum chemical calculations,and/or by comparing their CD spectra with those of the known compounds.Compounds 1 and 2 are the first examples of biscembranoids bearing a 1,35-bridged lactone moiety,4 is the first biscembranoid comprising an uncommon oxetane ring,and 5 represents the first 36-peroxyl biscembranoid.Ximaolides Ⅰ(2),K(4) and F(9) exhibited interesting anti-inflammatory activity by the inhibition of LPS-induced TNF-α protein release in RAW264.7 macrophages.     

Structural basis for the discrepancy of spectral behavior in C-H stretching band between steroids and long chain hydrocarbon compounds

The discrepancies of the spectral behavior for the C-H stretching band between some long chain hydrocarbon compounds and steroids were investigated. At low temperature, the C-H stretching bands exhibit complex fine structure in steroids but remain simple in long chain hydrocarbon compounds. MM3 molecular mechanics calculation indicates that, for long chain hydrocarbon compounds, the C-H groups vibrate with large scale coupling. There exist a few bands where the C-H groups vibrate in synchronous and inphase mode. Thus the variations of dipole moment for these bands are enhanced and the intensities are obviously stronger than others and cover other band in the spectra. This is just the reason why the C-H stretching bands are simple even at low temperature environment. Nevertheless, for the steroids, the C-H stretching bands vibrate with local coupling mode. The synchronous enhancement effect does not occur, the differences of intensities for various modes are not as large as those in long chain hydrocarbo     

Detailed investigation of optimized alkali catalyzed transesterification of Jatropha oil for biodiesel production

The non-edible oils are believed to be one of the major feedstock for the production of biodiesel in future.In the present study,we investigated the production of Jatropha oil methyl esters(JOMEs) via alkali-catalyzed transesterification route.The biophysical characteristics of Jatropha oil were found within the optimal range in accordance with ASTM standards as a substitute diesel fuel.The chemical composition and production yield of as-synthesized biodiesel were confirmed by various analytical techniques such as FT-IR,1H NMR,13 C NMR and gas chromatography coupled with mass spectrometry.A high percentage conversion,～96.09%,of fatty acids into esters was achieved under optimized transesterification conditions with 6 :1 oil to methanol ratio and 0.9 wt% Na OH for 50 min at ～60°C.Moreover,twelve fatty acids methyl esters(FAME) were quantified in the GC/MS analysis and it was interesting to note that the mass fragmentation pattern of saturated,monounsaturated and diunsaturated FAME was comparable with the literature reported values.     

Separation and characterization of petroleum asphaltene fractions by ESI FT-ICR MS and UV-vis spectrometer

Using heptane, toluene, and tetrahydrofuran (THF) as eluant, asphaltenes were fractionated into five fractions based on their polarity and solubility. The molecular composition of polar heteroatom species in both asphaltene and its fractions were analyzed by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The application of UV-vis spectrometer in characterizing asphaltene composition and measuring asphaltene concentration was discussed. About 11.9 wt% asphaltene components adsorbed permanently on silica gel in the extrography column after excessive elution with various solvents. In negative FT-ICR MS, the mass spectra show that acidic and neutral nitrogen-containing compounds such as N1 and N1S1 mainly existe in the first three less polar fractions, while oxygen-containing compounds such as O2 , O2S, O2S2 , O3 , and O4 show high relative abundance in more polar fractions. These results suggest oxygen-containing compounds have stronger adsorption ability with silica gel. It was observed that the double bond equivalence (DBE) distribution of N1 class species in the fractions shifted to higher values while the carbon number shifted to smaller numbers as polarity of fractions increased. This indicates that acidic and neutral N1 compounds with longer carbon chain and less aromaticity have less polarity compared with those with shorter carbon chain and stronger aromaticity. UV-vis absorbance indicats that fractions containing the most aromatic and most polar asphaltene have better absorbance at long wavelength, while the fractions that consist of least aromatic and least polar asphatlenes show high absorbance at short wavelength.     

BAND-LIKE TEXTURE OF ETHYLCYANOETHYL CELLULOSE MESOPHASE

In the ethyl-cyanoethylcellulose ((E-CE)C)/dichloroacetic acid (DCA) cholesteric liquid crystalline solution, the hand-like texture is formed when the mesophase aggregates with the disk-like texture grow to big enough and merge with each other with increasing concentration. The band-like texture is composed of parallel equidistant bright and dark alternative strips which are about 0.2-2.0 μm in width. In the band-like texture, the layers of ordered polymer chains are perpendicular to the solution film and the axes of helicoids are parallel to it. The width of the strips is different in different zones. Under the effect of an external magnetic field, the strips in the band-like texture first become wider and then narrower gradually.Moreover, the axes of helicoids in the (E-CE) C/DCA mesomorphic solution change from the direction normal to the magnetic field to the agreement with the magnetic field direction.