共查询到20条相似文献,搜索用时 93 毫秒
1.
Chen YC Sun WT Lu HF Chao I Huang GJ Lin YC Huang SL Huang HH Lin YD Yang JS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(4):1193-1200
The synthesis and brakelike performance of a new molecular system (1) consisting of a pentiptycene rotor and a 2-methyleneindanone brake are reported. The rotation kinetics of the rotor was probed by both variable-temperature (1)H and (13)C NMR spectroscopy and DFT calculations, and the switching between the brake-on and brake-off states was conducted by a combination of photochemical and electrochemical isomerization. Because of the greater steric hindrance between the rotor and the brake units in the Z form ((Z)-1) than in the E form ((E)-1), rotation of the rotor is slowed down 500-fold at room temperature (298 K) on going from (E)-1 to (Z)-1, corresponding to the brake-off and brake-on states, respectively. The (E)-1→(Z)-1 photoisomerization in acetonitrile is efficient and reaches an (E)-1/(Z)-1 ratio of 11:89 in the photostationary state upon excitation at 290 nm, attributable to a much larger isomerization quantum efficiency for (E)-1 versus (Z)-1. An efficient (Z)-1→(E)-1 isomerization (96%) was also achieved by electrochemical treatment through the radical anionic intermediates. Consequently, the reversibility of the E-Z switching of 1 is as high as 85%. The repeated E-Z switching of 1 with alternating photochemical and electrochemical treatments is also demonstrated. 相似文献
2.
D Hesek M Lee J Zajíček JF Fisher S Mobashery 《Journal of the American Chemical Society》2012,134(33):13881-13888
We describe a practical, multigram synthesis of (2Z,6Z,10Z,14Z,18E,22E)-3,7,11,15,19,23,27-heptamethyl-2,6,10,14,18,22,26-octacosaheptaen-1-ol [(Z(4),E(2),ω)-heptaprenol, 4] using the nerol-derived sulfone 8 as the key intermediate. Sulfone 8 is prepared by the literature route and is converted in five additional steps (18% yield from 8) to (Z(4),E(2),ω)-heptaprenol 4. The use of Eu(hfc)(3) as an NMR shift reagent not only enabled confirmation of the structure and stereochemistry of 4, but further enabled the structural assignment to a major side product from a failed synthetic connection. The availability by this synthesis of (Z(4),E(2),ω)-heptaprenol 4 in gram quantities will enable preparative access to key reagents for the study of the biosynthesis of the bacterial cell envelope. 相似文献
3.
Z-configured 1,4-diene or β,γ-unsaturated carbonyl systems are readily available by the Wittig reaction. Isomerization required for access into the E-series can easily be accomplished by irradiation using an ordinary tungsten lamp and diphenyl disulphide sensitizer. There is very little formation of conjugated isomers (less than 1%). 相似文献
4.
Dr. Thi Minh Thi Le Dr. Thibaud Brégent Prof. Dr. Philippe Jubault Prof. Dr. Thomas Poisson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(52):e202201514
Herein, we disclosed the contra-thermodynamic E→Z isomerization of alkenyl silanes, according to the in situ formation of a chromophoric species, in the presence of rac-BINAP as the catalyst. The reaction carried out in DMSO or CH3CN under irradiation at 405 nm allowed the interconversion of the E-isomers into the Z-congeners in good to excellent yields and outstanding Z/E selectivities, on 18 examples. Finally, the mechanism of this E→Z isomerization was studied to get insight into the reaction mechanism. 相似文献
5.
Richa Rashmi Dr. Pankaj Kumar Yadav Aniruddha Seal Prof. Manikandan Paranjothy Prof. Upakarasamy Lourderaj 《Chemphyschem》2023,24(2):e202200640
Our recent work on the E−Z isomerization reaction of guanidine using ab initio chemical dynamics simulations [Rashmi et al., Regul. Chaotic Dyn. 2021 , 26, 119] emphasized the role of second-order saddle ( SOS ) in the isomerization reaction; however, we could not unequivocally establish the non-statistical nature of the dynamics followed in the reaction. In the present study, we performed thousands of on-the-fly trajectories using forces computed at the MNDO level to investigate the influence of second-order saddle in the E−Z isomerization reaction of guanidine and the role of intramolecular vibrational energy redistribution (IVR) on the reaction dynamics. The simulations reveal that while majority of the trajectories follow the traditional transition state pathways, 15 % of the trajectories follow the SOS path. The dynamics was found to be highly non-statistical with the survival probabilities of the reactants showing large deviations from those obtained within the RRKM assumptions. In addition, a detailed analysis of the dynamics using time-dependent frequencies and the frequency ratio spaces reveal the existence of multiple resonance junctions that indicate the existence of regular dynamics and long-lived quasi-periodic trajectories in the phase space associated with non-RRKM behavior. 相似文献
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7.
Siewertsen R Strübe F Mattay J Renth F Temps F 《Physical chemistry chemical physics : PCCP》2011,13(34):15699-15707
The ultrafast C→E ring-opening reactions of four selectively modified furylfulgides have been studied by means of ultrafast broadband transient absorption spectroscopy after femtosecond laser excitation at λ = 500 nm. A large difference in the dynamics was found in the case of benzannulation at the furyl moiety as an example for an electronic effect by extension of the conjugated π-electron system compared to furylfulgides carrying sterically different alkyl substituents at the central cyclohexadiene (CHD) ring. The measured very similar spectro-temporal absorption maps for the furylfulgides with a methyl or isopropyl group at the CHD ring or an intramolecular alkyl bridge from the CHD to the furyl moiety showed two distinctive excited-state absorptions with slightly different decay times. The first time constant (τ(1) = 0.39-0.57 ps) was assigned to the rapid departure of the excited wavepacket from the Franck-Condon region. The slightly longer second decay time of τ(2) = 0.66-0.92 ps, depending on the compound, was attributed to the electronic deactivation and ring-opening through a conical intersection to the S(0) state. In contrast, the benzannulation at the furyl moiety was found to lead to a bi-phasic excited-state decay with τ(2) = 4.7 ps and a much slower additional contribution of τ(3) = 17.4 ps, ≈25 times longer compared to the normal furylfulgides. The drastic change is attributed to a trapping of excited molecules in a local potential energy minimum en route to the conical intersection. 相似文献
8.
XU Wen-Guo ZHANG Rui-Chun CHANG Hong-Yan 《结构化学》2009,28(9):1067-1076
Clusters XY2Z species are theoretically investigated with density functional theory (DFT) method. The results show that for LiP2C, LiAs2Ge and KAs2C species, the C2v isomer is the most stable planar structure, while for other species the Cs isomer is the most stable planar structure at the B3LYP/6-311+G* level. Wiberg Bond Index (WBI) and Nucleus-Independent Chemical Shift (NICS) values indicate the existence of delocalization in stable planar structures. A detailed Molecular Orbital (MO) analysis further reveals that planar isomers of these species have strong aromatic character, which strengthens the structural stability and makes them closely connect with the concept of aromaticity. 相似文献
9.
A new method for preparing (2Z, 4Z, 6Z)-4,5-diethyloxepinodicarboxylate by one-step is described. The synthesis of several oxepines and azepines derivatives was carried out by the reaction of substituted furans or pyrroles with diethyl acetylenedicarbox-ylate in boiling toluene. The effect factors for this reaction were discussed and reaction condition was optimized. 相似文献
10.
Mid-to-late transition metal complexes that feature terminal, multiply bonded ligands such as oxos, imides, and nitrides have been invoked as intermediates in several catalytic transformations of synthetic and biological significance. Until about ten years ago, isolable examples of such species were virtually unknown. Over the past decade or so, numerous chemically well-defined examples of such species have been discovered. In this context, the presentreview summarizes the development of 4- and 5-coordinate Fe(E) and Co(E) species under local three-fold symmetry. 相似文献
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12.
We have explored the structures and stabilities of AuXe n Z (n = 1–3, Z = ?1, 0, +1) cluster series at CCSD(T) theoretical level. The electron affinities and ionization potentials are correlated to the HOMO–LUMO gaps. The role of the interaction was investigated using the natural bond orbital analysis. 相似文献
13.
Aldoshin S. M. Berry F. J. Zakharov A. V. Sadekov I. D. Safoklov G. V. Tkachev V. V. Shilov G. V. Minkin V. I. 《Russian Chemical Bulletin》2004,53(1):66-73
The structures of -tellurocyclohexenals and their nitrogen analogs, viz., -methyltellurocyclohexenal (6), -(4-ethoxyphenyltelluro)cyclohexenal (7), di(2-formylcyclohexen-1-yl) telluride (8), -(4-ethoxyphenyltelluro)cyclohexenylidene(4"-methylaniline) (9), -bromotellurenylcyclohexenylidene(4"-methylaniline) (10), and -bromotellurenylcyclohexenal (4-methylbenzoyl)hydrazone (11), were studied by X-ray diffraction analysis. Compounds 6—11 have a Z configuration at the double bond, which provides the formation of intramolecular OTe or NTe coordination bonds. The bonds about the Te atom have a T-shaped configuration. There is only one of two possible OTe coordination bonds in dialdehyde 8 and, consequently, this compound belongs to the 10-Te-3-tellurane structural type. Hydrazone 11 possesses both NTe and OTe intramolecular coordination bonds. Taking into account these interactions, the coordination polyhedron of the tellurium atom can be considered as a trigonal bipyramid. The intramolecular OTe or NTe coordination bond lengths in compounds 6 (2.692 ), 7 (2.657 ), 8 (2.657 ), and 9 (2.690 ) are 0.9—1.0 smaller than the sums of the van der Waals radii of the corresponding atoms. These bond lengths in compounds 10 (2.170 ) and 11 (2.203 ) are almost equal to the standard covalent bond length. 相似文献
14.
Burghart J Sorg A Brückner R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(23):6469-6483
Stereoselective syntheses of 1,6‐bis(tributylstannyl)hexa‐1,3,5‐trienes, 1,8‐bis(tributylstannyl)octa‐1,3,5,7‐tetraenes, and 1,10‐bis(tributylstannyl)deca‐1,3,5,7,9‐pentaenes with various methylation patterns were achieved based on stereocomplementary C?C bond‐forming reactions. All‐E isomers resulted from Ramberg–Bäcklund rearrangements of distannylated diallyl‐, allylpentadienyl‐, or bis‐ (pentadienyl)sulfones. Mono‐Z‐configured 1,ω‐bis(tributylstannyl)‐1,3,5‐polyenes emerged from (Sylvestre–)Julia olefinations of Bu3Sn‐substituted enals or dienals with Bu3Sn‐substituted allyl or pentadienyl benzothiazolylsulfones. Related Ramberg–Bäcklund approaches provided all‐E‐1‐bromo‐6‐(tributylstannyl)hexa‐1,3,5‐triene but not all‐E‐1‐(tetramethyldioxaborolanyl)‐6‐(tributylstannyl)hexa‐1,3,5‐triene. 相似文献
15.
Ohmura T Oshima K Suginome M 《Angewandte Chemie (International ed. in English)》2011,50(52):12501-12504
Double take: β-Borylallylsilanes have been synthesized by the regioselective silaboration of terminal alkynes followed by palladium-catalyzed double-bond migration of the resulting β-borylalkenylsilanes. The stereoselectivity of the double-bond migration can be controlled by additives, thus leading to the stereocomplementary synthesis of (E)- and (Z)-β-borylallylsilanes. 相似文献
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17.
Oleksiy V. Grygorovych Oleksiy V. Nevskii Sofia M. Moskalenko Vasyl G. Pivovarenko Andrey O. Doroshenko 《Central European Journal of Chemistry》2010,8(4):766-782
Protolytic interactions in the series of prospective fluorescent ratiometric wide-range pH indicators — structurally rigid
analogs of 2,6-distyrylpyridine — (3E,5E)-3,5-dibenzylidene-8-phenyl-1,2,3,5,6,7-hexahydrodicyclopentano[b,e]pyridine — were
investigated. The pyridine nitrogen atom basicity in these compounds is significantly lower in comparison with that of unsubstituted
heterocycle and 2,6-distyrylpyridine. The photochemical E→Z photoisomerization and the side benzene rings substituents influence
on the acid-base equilibria were studied. The complex multi-stage mechanism of the acid-base interactions of the polysubstituted
compounds was elucidated. The most significant spectral effects were typical to the N,N-dialkylamino substituted compounds
of the investigated series. The widest pH sensitivity interval covering nearly the full range of 0–14 units was demonstrated
for compounds with both proton donor and proton acceptor substituents.
相似文献
18.
《Tetrahedron: Asymmetry》2001,12(18):2581-2587
From stereoisomeric α,β-unsaturated nitriles (E,Z)-1, the recombinant nitrilase AtNIT1 from Arabidopsis thaliana hydrolyses the (E)-isomers exclusively to the corresponding (E)-carboxylic acids (E)-2 with high specificity. The (E)-selectivity can also be utilised for the preparation of the isomerically pure nitriles (Z)-1. From (E,Z)-2-hydroxycinnamonitrile (E,Z)-3, the otherwise difficult obtainable (Z)-3 was prepared in 66% isolated yield. With β,γ-unsaturated (E,Z)-3-heptenenitrile (E,Z)-4, however, (E)-selectivity was not observed. AtNIT1 exhibits not only diastereoselectivity but also regioselectivity. From a mixture of the four isomers A–D of 3-(2-cyanocyclohex-3-enyl)propenenitrile 6, exclusively isomer D ((E)-cis-6) was hydrolysed to 3-(2-cyanocyclohex-3-enyl)propenoic acid (E)-cis-7, as stated by X-ray crystal structure. Only after complete conversion of D and high enzyme concentrations, isomer C ((E)-trans-6) was hydrolysed to a small extent. 相似文献
19.
Yang Q He R Shen W Li H Li M Zhu C Lin SH 《The journal of physical chemistry. A》2011,115(48):14022-14033
Although difluorobenzenes (DFBs) are well-known organic molecules to understand the electronic structure and spectroscopy of benzene and its derivatives, few theoretical investigations have been performed to simulate their fine spectra and assign their vibrational bands. In this work, the fluorescence excitation (FEX) spectra of the first excited singlet states for three DFBs molecules (para-, meta- and ortho-difluorobenzene) were simulated by the Franck-Condon calculations with the displaced harmonic oscillator approximation plus the distorted correction. The calculated results indicated that the spectral profiles of three DFBs are primarily described by the Franck-Condon progression of their totally symmetric vibrational modes. Specifically, it is found that modes v(3) and v(5) of para-DFB, v(8) and v(9) of meta-DFB, and ortho-DFB play the most important roles in the fluorescence spectra. By taking into account the contributions of the distorted effect, we could assign most of the dominant overtones from the nontotally symmetric vibrational modes, and the results agree well with the experimental assignments. Some inferred and unassigned vibrational transitions in experiment were confirmed according to the present calculated results. In addition, in the simulated fluorescence spectra, we tentatively assigned several combination bands with relative moderate intensity and weak vibrational lines which appeared in the experimental observations but the corresponding assignments were not given. The present work reproduced satisfactorily the experimental FEX spectra of p-, m-, and o-DFBs derivatives and provided a useful method to simulate the FEX spectra of dihalogenated benzene molecules. 相似文献
20.
Nevin Karabocek Asligul Kucukdumlu Pinar Ekmekcioglu Serdar Karabocek 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1007-1014
Monomeric copper(II) and nickel(II) complexes with tetradentate two new ligands, 2,2′-[(2E,5E)-hexane-2,5-diylidenedi- nitrilo]dibenzenethiol(H2L) and 2-hydroxybenzaldehyde (2E,5E)-hexane-2,5-diylidenehydrazone(H2L1) have been synthesized and characterized by elemental analyses, magnetic moments, molar conductance, 1H-NMR and 13C-NMR, IR, mass spectral studies, theoretical calculations (MM2 and AM1) molecular methods. The mononuclear metal complexes of H2L and (H2L1) were found to have a 1:1 metal:ligand ratio. Elemental analyses, stoichiometric and spectroscopic data of metal complexes indicated that the metal ions were coordinated to the sulphur (-SH) and/or (-OH) oxygen and imine nitrogen atoms (C = N). All of the data obtained from spectral, and molecular mechanics (MM2) or semi empirical calculations (AM1) studies support the structural properties of ligands and its Cu(II) and Ni(II) metal complexes. 相似文献