共查询到20条相似文献,搜索用时 78 毫秒
1.
Lu Luo Shuai Tang Jiangyue Wu Shiwei Jin Hua Zhang 《Chemical record (New York, N.Y.)》2023,23(4):e202300023
Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required. 相似文献
2.
本文用紧束缚法的EHMO三维晶体轨道程序进行计算求得了C60,K3C60和K6C60的能带结构,并得到了一系列过去未曾见过报导的原子投影态密度、轨道、原子重叠布据、原子电荷、轨道矢量等数据。从这些能带图中可以充分说明三种物质的区别,并可解释K3C60的超导性和C60与K6C60的绝缘性。 相似文献
3.
The densities (ρ), viscosities (η), refractive indices (nD), and speeds of sound (u), of binary mixtures of pyridine with 1-hexanol, 1-heptanol, 1-octanol and 1-decanol, including those of pure liquids, were measured over the entire composition range at 303.15 K and atmospheric pressure. From these experimental data, the values of excess molar volumes (VE), deviations in isentropic compressibilities (Δks), viscosities (Δh), molar refractions (ΔRm), apparent and partial molar volumes (Vf,2 and ), apparent and partial molar compressibilities (Kf,2 and ), of alkanols in pyridine and their corresponding deviations (ΔV and ΔK) were calculated. The variations of these parameters with composition of the mixtures suggest that the strength of interactions in these mixtures follow the order: 1-hexanol>1-heptanol>1-octanol>1-decanol. All the excess and deviation functions were fitted to Redlich-Kister polynomial equation to determine the fitting coefficients and the standard deviations. 相似文献
4.
Solvatochromic vibrational frequency shifts of a few different infrared (IR) probe molecules have been studied by carrying out quantum chemistry calculations for a number of their water clusters. We are particularly focused on the vibrational solvatochromic and electrochromic effects on the CO, CN, and CF stretch modes in carbon monoxide, acetone, 4-cyanopyridine, p-tolunitrile, fluorobenzene, and 3-fluoropyridine. Using multiple interaction site antenna model, we show that their solvatochromic vibrational frequency shifts can be successfully described by considering spatially nonuniform electrostatic potential generated by the surrounding water molecules. It turns out that the CO and CF stretch mode frequencies are approximately proportional to the solvent electric field projected onto the bond axes, whereas the vibrational frequencies of the nitrile stretch mode in 4-cyanopyridine and p-tolunitrile are not. Consequently, it is confirmed that the vibrational Stark tuning rates of the CO and CF stretching modes can be directly used to describe their solvatochromic frequency shifts in condensed phases. However, the nitrile stretch mode frequency shift induced by solvent electrostatic potential appears to be more complicated than its electrochromic phenomenon. To examine the validity of the distributed interaction site model for solvatochromic frequency shifts of these vibrational chromophores, we thus calculated the vibrational Stark tuning rates of the CO, CN, and CF stretch modes and found that they are in good agreement with the experimental results found in literatures. This confirms that a collection of properly chosen distributed interaction sites can be an excellent electric antenna sensing local electrostatics that affects on vibrational frequencies of IR probe modes. 相似文献
5.
Takuya Shimajiri Prof. Dr. Takanori Suzuki Dr. Yusuke Ishigaki 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22436-22441
Since carbon–carbon (C−C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp3)−C(sp3) single bond by light and heat. This flexibility of a C−C bond was demonstrated by X-ray analysis and Raman spectroscopy of hexaphenylethane (HPE)-type hydrocarbons with two spiro-dibenzocycloheptatriene units, the intramolecular [2+2] photocyclization of which and thermal cleavage of the resulting cyclobutane ring both occur in a single-crystalline phase. The force constant of the contracted C−C bond is 1.6 times greater than that of the expanded bond. Since formation of the cyclobutane ring and contraction of the C−C bond lower the HOMO level by approximately 1 eV, the oxidative properties of these HPEs with a flexible C−C bond can be deactivated/activated by light/heat. 相似文献
6.
Ruthenium catalyzed C−H activation is well known for its high tolerance towards the functional group and broad applicability in organic synthesis and molecular sciences, with significant applications in pharmaceutical industries, material sciences, and polymer industry. In the last few decades, enormous progress has been observed with ruthenium-catalyzed C−H activation chemistry. Notably, the vast majority of the C−H functionalization known in the literature are intermolecular, although the intramolecular variant provides fascinating new structural facet starting from the simple molecular scaffolds. Intramolecular C−H functionalization is atom economical and step efficient, results in less formation of undesired products which is easy to purify. This has created a lot of interest in organic chemistry in developing new synthetic strategies for such functionalization. The focus of this review is to present the relatively unexplored intramolecular functionalization of C−H bonds into C−X (X=C, N, O, S) bonds utilizing versatile ruthenium catalysts, their scope, and brief mechanistic discussion. 相似文献
7.
8.
9.
JR Frost CM Pearson TN Snaddon RA Booth SV Ley 《Angewandte Chemie (International ed. in English)》2012,51(37):9366-9371
Going for the hat-trick: The synthesis of the entire callipeltoside family of natural products is described. Key to this synthesis was the coupling of the di-ene-yne and pyran fragments by a diastereoselective alkenylzinc addition allowing rapid access to the common aglycon. Attachment of each relevant L-configured sugar resulted in the first total synthesis of callipeltoside B, and the syntheses of callipeltosides?A and C. 相似文献
10.
Dr. Sabrina Giofrè Letizia Molteni Prof. Egle M. Beccalli 《European journal of organic chemistry》2023,26(2):e202200976
This Review summarizes the advances in the catalytic enantioselective mono- and difunctionalization of alkenes, highlighting the fundamental role of ligands. Several types of asymmetric reactions have been developed involving different bonds formation, C−O, C−N and C−C, highlighting the urgency to go ahead in the search for new ligands and synthetic methodologies in order to improve the control over the reaction selectivity and activity and thus, to increase the applications in the synthesis of heterocyclic scaffolds and biologically active compounds. The Review is organized into paragraphs, which discuss the type of bond formed during the nucleopalladation, C−O, C−N, C−C bonds, and the type of reaction involved. 相似文献
11.
C60和C70的制备,分离及物化性质研究 总被引:4,自引:1,他引:4
Kr(a|¨)tschmer,Huffman和他们的同事首先报道了制备C_(60)和C_(70)混合物的方法,我们利用Kr(a|¨)tschmer方法,但简化了装置合成了C_(60)和C_(70)合成方法基本原理为:当强电流使 相似文献
12.
C_(60)、C_(70)与过氧苯甲酰反应的动力学研究胡波,薛万华,张法义,尚振锋,马克勤,臧雅茹,赵学庄(南开大学化学系,天津,300071)关键词C_(60),C_(70),动力学Kratschmer等人[1]的发现使制备宏观量的C(60)和C(70... 相似文献
13.
C—N,C—O键偶联是有机合成中的一类重要反应,铜催化的偶联反应是该类化学键形成中的主要手段之一,相比钯等过渡金属,金属铜具有低毒、廉价、反应条件温和等优点.按照所形成化合物的结构类型综述了铜催化C—N,C—O键偶联反应的最新研究进展. 相似文献
14.
在B3LYP/6-311G(d)和QCISD(t)/6-311+G(2df)水平下计算得到了[C, N, N, P]体系的9个异构体、20个过渡态及一些相关的解离碎片, 并研究了异构体之间的异构化过程, 讨论了该体系异构体的结构与稳定性. 结果表明在得到的9个异构体中, 具有2A′电子态的、非线型链状NCNP, NCPN, CNPN和CNNP 4个异构体是较稳定的. 其余异构体由于易于重排或是解离, 稳定性较低. 研究同时给出了这4个异构体的振动频率、转动常数、偶极矩、第一绝热电离能和绝热电子亲合能等相关数据, 为可能的实验和星际光谱观测提供相关的理论数据. 得到的计算结果与等价电子体系SiNNP进行了比较. 相似文献
15.
《有机化学》1993,(2)
The Koenig-Knorr method is still the most useful method for the synthesis of glycosides thoughpartly inherent disadvantages of this method could not be overcome. Recently Schmidt et al. reportedthat glycosyl trichloroacetimidates can be used to synthesize C, O and S-glycosides stereoselectively inhigh yield under mild reaction conditions. 相似文献
16.
A. N. Isaev 《Russian Journal of Inorganic Chemistry》2013,58(7):817-823
Molecular complexes formed by different forms of carbocations (carbenium ions) and carboanions with water, acetylene, and methane molecules have been calculated by the MP2/6-311++G(2df,2pd) method. In complexes with water where the carbon atom of the carbocation (carboanion) acts as the proton donor (acceptor), the energies of the C-H?O and O-H?C hydrogen bonds turn out to be approximately the same being 13–20 kcal/mol for carbocation (carboanion) species differing in the valence state of the carbon atom. Two types of C-H?C interactions have been revealed depending on the charge at the bridging hydrogen atom, which is determined by the hybridization of the donor carbon atom. The C-H?C interaction energy in molecular complexes with the positively charged hydrogen atom (carboanion complexes with acetylene) is an order of magnitude higher than in the complexes where the bridging hydrogen atom has an excess of electron density (carbocation complexes with methane). In all the complexes under consideration, the covalent C-H bond involved in interaction is elongated, and the negative charge is transferred from the acceptor to the donor. 相似文献
17.
在哺乳动物金属硫蛋白的61或62个氨基酸残基中,有20个十分保守的Acysteines,它们通常结合7个二介后过渡金属离了如ZN2+和Cd2+[1,2]等,并形成两个结构域[3],在N-端B-donain[M(I)3-Cys9]的中,3个二价后过渡金属离子均以两上端基巯基和两个桥基巯的相同方式与肽链上的半胱氨酸配位,而在C-端的a-domain[M(I)-Cys11]配位方式分为两类;两上二价后过渡金属离子分别与3个桥基巯基和1个端基配位,另两个二价后过渡金属的配位方式与中的相似,金属硫蛋白在一级序列上最显著的特征是存在多个片段,其中X是非半胱氨酸氨基酸残基[1,7]. 相似文献
18.
Paul J. Dyson Petra Escarpa Gaede Brian F. G. Johnson John E. McGrady Simon Parsons 《Journal of Cluster Science》1997,8(4):533-545
On reaction with Ru3(CO)12, isopropenylbenzene and 4-phenyl-l-butene undergo hydrogenation, to yield the clusters, Ru6C(CO)14(6-C6H5CHMe2) 1 and Ru6C(CO)14(6-C6H5C4H9) 2, respectively. With allylbenzene, both hydrogenation and isomerization occurs affording Ru6C(CO)14(6-C6H5C3H7) 3 and Ru6C(CO)14(6-C6H5C3H5) 4. The structures of 1 and 2 have been established by single crystal X-ray diffraction. One of the Ru–Ru bond lengths in 2 is unusually long and extended Hückel molecular orbital calculations have been used in an attempt to rationalize this feature. 相似文献
19.