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.     

Ab Initio Study on the Isomerization and Dehydrogenation of Methylnitrene

The ab initio calculations were performed at the RHF/4-31G level with the reaction pathways of the iso-merization and dehydrogenation of methylnitrene by the intrinsic reaction coordinate method. The results show that the transformation from methylnitrene to methylenimine would be very easy. This accountes for the experimental fact that one couldn' t find the methylnitrene, but only obtained the methylenimine in the pyrolysis of methyl azide. The mode-selective study reveals the reaction coordinates (IRC) of isomerization and dehydrogenation of methylnitrene are associated with the molecular deformation mode of 1191 cm-1 and the methyl group unsymmetrical stretch mode, respectively. The coupling between normal coordinates is favourable to select the reaction channel of isomerization.     

Ab Initio Study on the Anti-HIV Activities of Hydroxyflavones

1 INTRODUCTION AIDS, in other words, Acquired Immunodefici-encysyndrome, is a viral contagious disease withhigh death rate. However, effective treatment againstit has not appeared so far. At present, about 100kinds of natural compounds that could be extractedfrom natural products or artificially synthesized havebeen found to have anti-HIV activities to some ex-tent. They belong to flavonoid, terpenoid, steroid, cou-marin, peptide, alkaloid etc., respectively. Previousstudies show that…     

Ab Initio Study of the Oxygen Atom Abstracting Hydrogen from Difluoromethane and Dichloromethane

ThemajorfiresuppressionagentsusedinconfinedspacesortoprotectelectronicsareCFsBrandCF2ClBr.Howeverbecauseoftheirozonedepletionpotential,theirproductionisnowbanned.Thesearchfornewflamesuppressantswhichareeffective,nontoxicandhaveIowglobalenvironmentalimpacthassparkedincreasedinterestinthemechanismsoffiresuppressionandthedevelopmentofpredictiveflamemodels1-2.KineticdataforthereactionsofOatomswithhalogenatedmethanesareneededtomodelthecombustionchendstry.Manystudiesaboutithavebeencarriedoutbyex…     

Ab Initio Study of NH_3-CH_3OH Neutral and Ionic Clusters

HydrogenbondingandprotonboferhavebeendrawingtheattentionofboththeoreticiansandexPeriInentalistsforalongthoebecauseoftheboortanceinelucidatingvariousPhenomenainchemicalandbiologicalenvirOIUnentsll.21-InthosemuliPhotonionhaionStUdiesofanunoniaormethanolhydrOgen-bond6dclustcrs,tbemassSPeCbeexhibitedamajorsequenceoftheprotonatedclUSterionswe,Wor(CH,W,whichwerePrOducedbyioIhaaionofneutralclUStersfollowedbyintalUSterPrototranSferreactions[3,4].Tomodaetalsuggestedthattheannnoniadhoercation…     

Ab Initio Study of the Excited State Decomposition Reactions of Monothioformic Acid

IntroductionTherehasbeenconsiderableinterestinrecentyearsinthetheoreticalstudyofthemonothioformicacid1ed.However,mostofthemhaveconcentIatedontheelectronicproperties,isomerizationandintramolecularhydrogenshiftreactionsoftheacid,andstudiesonitschemicalreactionshaverarelybeenrepofted.Recently,wereportedonthetheoreticalstudyofthegroundstateunimolecularpyrolysisofmonothioforndcacid,andtheresultsshowedthathightemperatureisneededforitsgroundstatedecompositionreactions.Asapotentialinterstellarcompoun…     

Ab Initio and Density Functional Study on the First Hyperpolarizabilities of Squaric Acid Homologues

The first hyperpolarizabilities of four squaric acid homologues: squaric acid, 1,2-dithiosquaric acid,1,2-diselenosquaric acid and 1,2-ditellurosquaric acid have been calculated using ab initio and DFT methods. The effects of equilibrium geometries, basis set and electron correlation on the first hyperpolarizabilties of these molecules were investigated. The frequency dispersion effect and solvent effect, which are essential to get reliable outputs in comparison to the experimental results, have also been explored. On the basis of these investigations, it is worthy to point out that the heavy atom effect takes effect for these squaric acid homologues.     

Ab Initio Study of the Acetylene–Allene Rearrangement in 2-Propargylpyrrole, 2-Propargylfuran, and 2-Propargylthiophene

Ab initio (MP4/6-31G*//RHF/6-31+G*) calculations have been performed to study the acetylene–allene rearrangement in X–CH₂–CCH propargyl systems, where X = ethenyl, E-1-butadienyl, 2-pyrrolyl, 2-furanyl, and 2-thienyl. The spatial and electronic structures, as well as the relative stability, of the initial and final acetylene structures and the corresponding allenes are examined. Migration of the triple bond from the terminal position into the chain, including the stage of allene structure formation, is shown to be thermodynamically favorable for the whole series of compounds. The propargyl substituents of heterocycles isomerize as readily as open diene systems. The differences in the isomerization energies in the series of allenyl- and 1-propynyl-substituted pyrrole, furan, and thiophene are mainly due to the differences in the nature of long-range interactions between heteroatoms and the tricarbon system.     

An Ab Initio Study of N_2O Decomposition on MgO Catalyst

Nl0isalwaysusedasoxidantinalotofoxidativecatalyticprocesses,suchastheoxidativecouplingofmethane(0CM),oxidativedehydr0genationofalkanesands0on,becauseitdecomPosestoprovideOadspeciesonmetal0xidecatalystsandleadstothespecificoxidativeselectivity.Forexample,itwasf0undthatf0rOCMreacti0nonMgOandLougOcatalystS,thereactiontemPeraturerequiredislowerwhenoneusesN20asoxidantthanusing0,'.TheunderstandingofN20dec0mposihon0nmetal0xidecatalystsandthepropertiesofthereIevant0adspeciesshouldbeagoodstarting…     

Ab Initio and RRKM Study of the Unimolecular Decomposition of Five-membered Ring Heterocyclic （X：O,S,N-H）

Quantum mechanical and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations are carried out to study the thermal unimolecular decomposition of 2,5-dihydrofuran (1),2,5dihydrothiophene (2),and 3-pyrroline (3) at the MPW1PW91/6-31++G level of theory,and the results are in good agreement with the experimental values.The predicted high pressure limit rate constants (k(T)) in various states of activation energy and pre-exponential (S1:(A(calc.),E a(calc.)),S2:(A (calc.),E a(exp.)),and S3:(A (exp.),E a(calc.))) for the thermal decomposition processes 1-3 were evaluated.Also,the fall-off pressures (P1/2) for compounds 1-3 in the states 1-3 are found to be (1.24×10-2,1.09×10-3,and 4.19×10-2mmHg),(1.24×10-2,1.63×10-3,and 2.79×10-2mmHg),and (1.24×10-2,1.63×10-3,and 4.19×10-2 mmHg),respectively.As the fall-off pressure of thermal decomposition process of compounds 1-3 is in the following order:P1/2(3)> P1/2(1)> P1/2 (2),the decomposition rates are as below:rate(3) 相似文献   

Ab Initio Study of the Reaction: H SO_2→HO SO

Intr0ducti0nThereactionofvariousmolecularandatomicspecieswithsulfurdioxidehasbeenthesubjectofmanykineticstudiesmainIybecauseofitsinvolvementinmany0fthechemi-calreacti0ns0ccurringintheupperatmosphereandals0becauseofitsindustrialsignifi-cance.I-2Theintermediatesinv0lvedinthereactionareusuallynotdirectlyobservable.Forexample,thegeometryoftheSO2.Hadductisuncertain.TwopossiblestructUreshavetheHat0mbondedeithert0theSat0m,representedasHSO2,orbondedtoan0atom,representedasHOSO.ThestructUresaresh…     

Ab Initio Study of Neutral and Charged Copper Bromide (CuBr) n (+) Clusters (n?=?1–6)

A theoretical study in the framework of the density functional theory is performed to investigate the stability, the structural and electronic properties of both neutral and cationic copper bromide clusters (CuBr) _n ⁽⁺⁾, n = 1–6. The most stable isomers are found to be cyclic arrangements. Calculated infrared frequencies are compared with the available experimental spectra. The nature of the ionio-covalent bonding is characterized. The fragmentation, the ionization potentials are also investigated.     

Jahn-Teller Effect on Binary Indium Bromide─An Ab Initio Study

Amongindiumhandes,thestructuralchemistryofthebromidesisrichest.Whilethefirststudycantracebacktothebeginningofthecentury',thebinaryphasediagramhasonlyrecentlybeencompleted'-'duetotheunusualinstabilityofthiscompoundslikeInBr,In5Br=,InZBr3,In.Br7andIner,.Accordingtotheexperiment,thebinaryindiumbromidesareverysensitivetotheair,light,humidityandmechanicalstress.Theoriginoftheunusualinstabilityofthecompoundscreatedgreatinterestamongthetheoreticalchemists.Theresultsbasedonthesemi-empiricalquantU…     

An ab Initio Study of Tetrathiosquaric Acid

Inthepastfewdecades,sincetheoxocarbonanionsC.O.'-wererecognizedasmembersofanewclassofstabilizedcarbocyclicnonbenzenoidaromaticcompounds"',theknowledgeoftheirchemicalandphysicalpropertieshasbeendevelopingrapidly'Theiruniqueelectronicstructures,highdegreeofsymmetry,andestheticallybeauti-fulgeometrygeneratedafreshimpetustostudytheeffectofreplacingtheoxygensbyvariousfunctionalgroups,suchassulfur',andselenium[11.Analogoustotheoxocar-bondianions,thethioxocarbondianionscanbecharacterizedbythegeneralf…     

Ab Initio structure determination of vaterite by automated electron diffraction

"This is a mineral about which there has been much discussion" is a typical statement about vaterite in older standard textbooks of inorganic chemistry. This polymorph of CaCO(3) was first mentioned by H. Vater in 1897, plays key roles in weathering and biomineralization processes, but occurs only in the form of nanosized crystals, unsuitable for structure determination. Its structure could now be solved by automated electron diffraction tomography from 50 nm sized nanocrystals.     

Correlation of Quantitative Structure and Inhibition Phytotoxicity for Aromatic Compounds Using Ab Initio Method

1 INTRODUCTION Quantitative structure-activity relationship (QSAR) is one of the necessary methods to evaluate the ha- zards of organic chemicals. QSAR equation could be employed to forecast the biological activity of un- known compounds, which is significant for initial screening and evaluation of toxic compounds[1]. Aro- matic compounds are toxic organic compounds with relatively low water solubility, and their structure- activity relationship has been investigated with AM1 method[2]…     

Ab Initio Study on the Thermal Isomerization from 1,2-Butadiene to1,3-Butadiene

1.IntroductionFromexperboentalstUdyonthepyrolysisofcyclOPropenel'],R.D.Kem`a1I'1assumedthattheisomerizaionfrom1,2-butadienetol,3-butadienewasastePwisereaCtionwhichproceedsintWostepsviaadiradicalintermediate.ThepresentpaPerisatheoreticalstUdytogiveanideaofitsstereochemicalprocessbymeansofabinitiomethods.2.Resultsanddiscussion2.lComputationalProcedureThegeometriesofthereacbot,thetransitionstates,theintermediateandtheproductfortheisomerhaonfroml,2-butadienetol,3-butadienewereoptAnizedatabin…     

AB Initio MO Study of P--Si π Systems: Structures and Energies

The origin of the relative stability of isomers of 1,2-diphosphinodisilene and related compounds is discussed. The geometries of 18 isomers of (H 2 X)HE=EH(XH 2 ), (H 2 X)HE=EH(XH 2 ) 2+ , and HX=EH--HE=XH (E = C, Si; X = P, N) have been optimized at the MP2/6-311++G(d,p) level of theory. Since nitrogen and phosphorus have lone-pair electrons, six electrons can delocalize in four orbitals of (H 2 X)HE=EH(XH 2 ) (6e/4o), while four electrons can delocalize in four orbitals of (H 2 X)HE=EH(XH 2 ) 2+ and HX=EH--HE=XH (4e/4o). To examine the interaction that governs the structure and relative stability of their cis and trans (or cisoid and transoid) isomers, the ~ - * delocalization energies and isodesmic reaction energies of the compounds were calculated. It is concluded that the ~ - * delocalization affects the bending structure of disilene derivatives, and phosphorus substituents prefer 2e/4o and 4e/4o systems.     

Ab Initio Study on the Mechanism of Cycloaddition Reaction between Silylene Carbene （H_2Si=C：） and Acetone

The mechanism of cycloaddition reaction between singlet silylene carbene and acetone has been investigated with CCSD(T)//MP2/6-31G method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. One consists of two steps: (1) the two reactants (R1, R2) firstly form a four-membered ring intermediate (INT4) through a barrier-free exothermic reaction of 585.9 kJ/mol; (2) Then intermediate (INT4) isomerizes to CH3-transfer product (P4.1) via a transition state (TS4.1) with energy barrier of 5.3 kJ/mol. The other is as follows: on the basis of intermediate (INT4) created between R1 and R2, intermediate (INT4) further reacts with acetone (R2) to form the intermediate (INT5) through a barrier-free exothermic reaction of 166.3 kJ/mol; Then, intermediate (INT5) isomerizes to a silicic bis-heterocyclic product (P5) via a transition state (TS5), for which the barrier is 54.9 kJ/mol. The presented rule of this reaction: the [2+2] cycloaddition effect between the π orbital of silylene carbene and the π orbital of π-bonded compounds leads to the formation of a four-membered ring intermediate (INT4); The unsaturated property of C atom from carbene in the four-membered ring intermediate (INT4) results in the generation of CH3-transfer product (P4.1) and silicic bis-heterocyclic compound (P5).     

6α-carboxy and 6α-carbamoyl,penicillins

Hemiacetal formation from 6α-formylpenicillins followed by oxidation has provided a series of esters of 6α-carboxypenicillins and the parent acid. Further derivatisation has afforded a 6α-carbamoylpenicillin.