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1.
1INTRODUCTIONTheconformationandvariousphysicalprope-rtiesofdichalcogencompoundsR-X-Y-R?(X,Y=O,S,Se,andTe)havebeenatopicofseveralexperi-mentalandtheoreticalinvestigations[1].CompoundscontainingS=SandS=Obondshavelongbeenpro-posedasintermediatesinorganicsynthesisand,onoccasion,asstableentities[2~18].Despitethecom-monlyusedrepresentationofS–Obondinsulfoxi-desandothersulfinylderivativesasS=O,sulfoxidesareinmanywaysbestdescribedasylideswithhighlypolarizedS–Oσ-bondbecauseofelectro-sta… 相似文献
2.
Danhong Zhou Yu Wu Qingmin Xu Linjing Yang Chunli Bai Zhongyen Tan 《Journal of inclusion phenomena and macrocyclic chemistry》2000,37(1-4):273-279
Molecular mechanics calculations were employed to study the inclusion of triethylbenzene isomers in -cyclodextrin and their solvation energy in aqueous solution. Trimethylbenzene penetrates partially into the cavity of -cyclodextrin to form 1 : 1 or 2: 1 host–'guest complexes. The interaction energy between host and guest is dominated by van der Waals energy. The inclusion complexes have higher solvationenergies than free -cyclodextrin. 相似文献
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Theoretical Study on the Structures and Stability of Isomers and Complex of [Si, C, O, O] System 总被引:1,自引:0,他引:1
Introduction[Si,C ,O ,O]systemhasattractedmuchattentioninthefieldsofchemistryandmaterials1 3becauseofthefollow ingseveralcauses .First,theinterestisthepotentialimpor tanceininterstellarspace .Heretofore ,SiC ,SiOandCOhavebeendetectedwithintheinterstellarmediumformanyyears,butno [Si,C ,O ,O]isomerswereobservedinthenebulae .FormanySi containingsystemshavebeenstudiedexperimentallyandtheoretically ,4 8andinviewofthepossibleexistenceofthe [Si,C ,O ,O]radicalininterstellarspace ,weselectthe… 相似文献
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A detailed singlet potential energy surface(PES) of [Si,C,O,O] system including a van der Waals (vdW) comples SiO……CO2,eight isomers,and twelve transiton states is investigated by MP2 and QCISD(T) (single-point)methods.At the final QCISD(T)/6-311 G(2df)//MP2/6-311G(d) level with zero-point energy included,the complex SiO……CO is found to be thermodynamically and kinetically the most stable species.Although eight ismoers are located as local energy minima,they are rather unstable toward isomerization to the dissociation fragments or comples.For the reaction of silocon atoms with carbon dioxide,two competitive reaction channels are found,and the primary pathway,which leads to the products of SiO and CO fragments,is the direct oxygen-abstraction process from carbon dioxide by silicon atom with a41.16 kJ/mol reaction barrier height.Our predications are in good agreement with previous experimental and theoretical studies. 相似文献
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QuantumChemistryStudyontheGeometricalStructuresofSmallCentipedo-boranes¥ZhongShi-Jun;WangYin-Gui;ZhangQian-Er(StateKeyLaborat... 相似文献
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The relative thermodynamic stabilities (relative enthalpies) of the E,Z-isomers of ,-dialkylsubstituted methyl vinyl ethers MeOC(R1)=CHR2 have been estimated by various computational methods including molecular mechanics, semiempirical, ab initio, and DFT calculations. The best performance, approaching the accuracy of the experimental method of chemical equilibration, is shown by the DFT calculations. Ab initio methods, provided that electron correlation is taken into account, are also satisfactory, but clearly less successful than the DFT calculations. The reliability of the semiempirical methods AM1 and PM3 is considerably less good, and varies in an unpredictable manner from case to case. The poorest general performance is shown by the MM2 and MM3 calculations, which may overestimate the relative stability of the Z isomer by as much as 18 kJ mol–1. 相似文献
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Introduction The organoaluminum azide compounds have been widely used in many fields. These compounds are used as the azidating agents,1-3 and the energetic materials which are always used in national defence industry and in space technology, especially to generate thin films of AlN in various chemical vapor deposition (CVD) sys-tems.4-6 Aluminum nitride has useful properties for coatings, especially for optical or optoelectronic devices, acoustic wave devices and electronic microcircuits.7 … 相似文献
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IntroductionTrinitrobenzenes(TNBs)havebeenthefocusofanumberofinvestigationsforalongtime.Manyoftheirderivatives,forexamplemeth... 相似文献
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Ten α,α,α′-trisubstituted cyclododecanones were synthesized and characterized by elemental analyses, infrared, 1^H NMR and 13^C NMR spectra, and X-ray diffraction. NMR data could not give conformational information clearly, but some of their ring skeleton conformations of cyclododecanone moiety were showed to remain the unchanged [3333]-2-one conformation with little distortion, while the others were changed to the [3324]-2-one conformation in their crystal structures. These are consistent with the results of molecular mechanics calculation with Sybyl 6.9 software and Tripos force field, and semi-empirical quantum calculation with AM 1 method in Gaussian 98 software. Two geminal substituting groups are located at α-corner carbon atom, and the third group is at α-side-exo carbon atom in both conformations. Both [3333]-2-one and [3324]-2-one conformations are present in a dynamic equilibrium in the solution, but only one preferred conformation exists in the crystal solid. 相似文献
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《Tetrahedron: Asymmetry》1998,9(17):2987-2998
The alkylation of the diastereomeric mixture of chiral morpholinone derivatives 4 and 5 occurs with good yield and trans induction. Cleavage of the alkylated products 6a,b,c,e gives enantiomerically pure uncommon (and sterically constrained) α,α′-dialkyl-α-aminoacids. The absolute configuration of the new stereocentres of 4, 5, 6 and 7 has been assigned on the basis of the 1H-NMR spectra and NOE measurements. 相似文献
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《Tetrahedron: Asymmetry》2000,11(22):4617-4622
Enantiomerically pure α,α′-diamino-dicarboxylic acids (R,R)-4, (S,S)-5 and (S,S)-7 have been synthesized starting from the glycine-derived chiral synthon (S,S)-1. 相似文献
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Ananda S. Hodage Prasad P. Phadnis Amey Wadawale 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):700-710
Abstract A series of α-substituted selenenyl acetophenone derivatives of the types, [PhC(OCH2CH2O)CH2Se]2, [PhC(OCH2CH2O)CH2SeR], (PhCOCH2Se)2, and [PhCOCH2SeR] have been prepared. These compounds have been characterized by elemental analyses, IR and NMR (1H, 13C, 77Se) spectroscopy. The compounds, [PhC(OCH2CH2)CH2Se]2 and (PhCOCH2Se)2 have been structurally characterized by single crystal X-ray diffraction analyses. The former shows intra-molecular Se‐?‐?‐O interaction, while the latter exhibits inter-molecular nonbonding Se‐?‐?‐O interaction. [Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental files: Additional text and figures.] 相似文献
13.
The geometries,electronic states and energies of Alm Pn ( m + n = 2 ~ 6)neutral and anionic clusters have been investigated using the density functional theory(DFT)method of Becke’s three-parameter hybrid exchange functional with the nonlocal correlation of B3LYP. Structural optimization and frequency analyses are performed with the basis of 6-311G( d). The calculations predict the existence of a number of previously unknown isomers(i. e. ,Al3P_ and AlmPn ( m + n.5)). The calculations have also predicted that small AlP and(AlP)2 clusters adopt two-and three-dimensional structures characteristic of Si2 and Si4 clusters,while the structures of the larger AlP clusters are different completely from those of Sin clusters with the same electrons. The results show that the structures with the singlet have higher symmetries,while those with the doublet have lower symmetries. The vertical detachment energy of AlmPn ( m + n = 2 ~ 6)are also discused and the adiabatic electron affinities of AlmPn(m + n = 2 ~ 6)and also discussed at the same level. The results agree satisfactorily with the anion photoelectron spectroscopy of aluminum phosphide clusters reported recently by Gomez et al. 相似文献
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《Tetrahedron: Asymmetry》1998,9(19):3411-3420
The alkylation of the diastereomeric mixture of the chiral morpholinone derivatives 5 and 6 occurs with good yield and a prevalence of the cis isomer. Cleavage of the alkylated intermediates 7b,c yields enantiomerically pure sterically constrained uncommon α,α′-dialkylated α-amino acids. The absolute configuration of the new stereocentres has been assigned on the basis of the 1H NMR spectra and NOE measurements. A model to explain the observed diastereoselection is proposed. 相似文献
15.
Ullah Hayat Ullah Hafeez Taha M. Khan F. Rahim F. Uddin I. Sarfraz M. Shah S. A. Ali Aziz A. Mubeen S. 《Russian Journal of Organic Chemistry》2021,57(6):968-975
Russian Journal of Organic Chemistry - New benzimidazole derivatives were synthesized by reacting substituted phenacyl bromides with 1H-benzimidazole-2-thiols. The synthesized compounds were... 相似文献
16.
《Tetrahedron: Asymmetry》2001,12(21):3047-3052
A study of the enantioselectivity exhibited by the lipase B from Candida antarctica in the transesterification of different α-substituted α-propylmethanols with vinyl acetate is shown. The best results are obtained when the large-sized (L) substituent of the alcohol is either a phenyl group or more especially a cyclohexyl group, although the reaction rates are lower than when linear or slightly branched groups are present. It is also found that ramification at the β-position of the L substituent has a deleterious effect on both lipase activity and enantioselectivity. Moreover, some α-substituted benzyl alcohols bearing medium-sized (M) substituents larger than an ethyl and smaller than a propyl group are resolved by means of this methodology with moderate-good enantioselectivities (E=46–57) and similar reaction rates. 相似文献
17.
L. A. Rodinovskaya K. S. Chunikhin A. M. Shestopalov 《Chemistry of Heterocyclic Compounds》2002,38(4):442-448
The reaction of benzaldehyde, -nitro ketone, and cyanothioacetamide in the presence of morpholine has given the novel 3,4-trans-2-R-5-cyano-2-hydroxy-3-nitro-4-phenyl-1,2,3,4-tetrahydropyridine-6-thiolates. It was found that the reaction occurs via the formation of 1-amino-2-cyano-4-nitro-5-oxo-3-phenyl-1,2-pentene-1-thiolate. In the case of -nitroacetophenone, 3,4-trans-4,5-trans-5-cyano-2-hydroxy-3-nitro-2,4-diphenylhexahydropyridine-6(1H)-thione was also obtained. The use of -nitroesters in place of the nitro ketones in the reaction leads to morpholinium 2-aryl-1-carbethoxy-3-cyano-1-nitro-3-thiocarbamoylpropyl-1-ates as the single product. 相似文献
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Dr. Filippo Favretto Dr. Jeremy D. Baker Dr. Timo Strohäker Dr. Loren B. Andreas Dr. Laura J. Blair Dr. Stefan Becker Prof. Dr. Markus Zweckstetter 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(14):5692-5695
Peptidylprolyl isomerases (PPIases) catalyze cis/trans isomerization of prolines. The PPIase CypA colocalizes with the Parkinson's disease (PD)-associated protein α-synuclein in cells and interacts with α-synuclein oligomers. Herein, we describe atomic insights into the molecular details of the α-synuclein/CypA interaction. NMR spectroscopy shows that CypA catalyzes isomerization of proline 128 in the C-terminal domain of α-synuclein. Strikingly, we reveal a second CypA-binding site formed by the hydrophobic sequence 47GVVHGVATVA56, termed PreNAC. The 1.38 Å crystal structure of the CypA/PreNAC complex displays a contact between alanine 53 of α-synuclein and glutamine 111 in the catalytic pocket of CypA. Mutation of alanine 53 to glutamate, as found in patients with early-onset PD, weakens the interaction of α-synuclein with CypA. Our study provides high-resolution insights into the structure of the PD-associated protein α-synuclein in complex with the most abundant cellular cyclophilin. 相似文献
20.
Prof. Dr. Christian Brückner Dr. Nivedita Chaudhri Dustin E. Nevonen Dr. Sayantan Bhattacharya Arthur Graf Elizabeth Kaesmann Dr. Ruoshi Li Dr. Matthew J. Guberman-Pfeffer Prof. Dr. Tomoyasu Mani Dr. Arunpatcha Nimthong-Roldán Dr. Matthias Zeller Dr. Adrien A. P. Chauvet Prof. Dr. Victor Nemykin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(65):16189-16203