排序方式: 共有108条查询结果,搜索用时 15 毫秒
81.
Prodeep Phukan 《Tetrahedron letters》2004,45(24):4785-4787
Iodine was found to promote quantitative acetylation of alcohols in a very short time with an equimolar amount of acetic anhydride under solvent-free conditions at room temperature. 相似文献
82.
Non-resonant microwave absorption (NRMA) studies of superconducting MgB2 and a sample containing ∼10% by weight of MgO in MgB2 are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB2 sample. A linear temperature dependence of the lower critical field H
c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB2 + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links.
The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB2 sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong
pinning of flux lines. This hysteresis saturates a few degrees below T
c while in the MgB2 + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning. 相似文献
83.
84.
Recently, donor stabilized divalent carbon(0) compounds have undergone intense experimental and theoretical investigation due to their strong electron rich character. In this Article, some new cyclic and acyclic carbon(0) compounds stabilized by differential coordination modes (such as abnormal, remote and a mixture of both) of N-heterocyclic carbenes are studied theoretically. The cyclic carbon(0) compounds proposed in this study are unusual in the sense that they contain a five membered ring consisting of only carbon atoms with a central carbon atom in the formal oxidation state of zero. All these compounds are found to be very strong nucleophiles which might have wide implications in catalysis. Calculation of first proton affinities of these molecules reveal that they are better σ donors than the carbon(0) compound supported by normal N-heterocyclic carbenes. Quantum chemical calculations indicate that these molecules possess very high donor-acceptor L → C bond strengths and are thermodynamically stable. Calculation of the bond dissociation energies for the complexation of one and two molecules of AuCl indicates the possible isolation of their gem dimetalated derivatives. 相似文献
85.
This paper is concerned with an experimental investigation of a comparison of the rheological performance of an ER fluid, consisting of a carrier with a range of solid phase sizes, in oscillatory squeeze-flow under DC conditions. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. It is seen that the dynamic performance of the fluid, in terms of the capacity for the transmission of imposed forces across the fluid, is highly dependent on the size of the dispersed solid phase and has an optimum value which is dependent on the mean value of the interelectrode gap. In addition the paper includes some measurements of the current through the fluid which may help to shed some further light on the mechanism of the ER effect. Finally the implications of the results to vibration control are discussed. Copyright 1999 Academic Press. 相似文献
86.
87.
Silica-supported p-toluene sulfonic acid is found to be an excellent catalyst for the Prins reaction to produce 1,3-dioxanes in good yields from olefins and aliphatic aldehydes in dichloromethane at room temperature and solventless microwave irradiation within a short reaction time. 相似文献
88.
A rapid process for decarboxylative bromination of α,β-unsaturated carboxylic acids have been developed using N,N-dibromo-p-toluenesulfonamide (TsNBr2). Treatment of cinnamic acids with TsNBr2 in presence of potassium carbonate in acetonitrile produces corresponding β-bromostyrenes at room temperature. Exclusive formation of (E)-β-bromostyrenes was observed in a stereoselective manner within a very short period of time (5–15?min). This method was further extended for obtaining 1-bromoalkynes from corresponding propiolic acids. Instantaneous formation of bromoalkynes was observed when the reaction was carried out in presence of DBU as a base in acetonitrile at room temperature. A wide variety of cinnamic acids and propiolic acids could be converted to corresponding β-bromostyrenes and 1-bromoalkynes respectively under mild reaction condition with high to excellent yield. 相似文献
89.
Sanchay Jyoti Bora Purabi Sarmah Prodeep Phukan Birinchi K. Das 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(9):m392-m394
The title compound, [Cu2(C7H5O2)4(C7H10N2)2], is a crystallographically centrosymmetric binuclear complex, with Cu atoms [Cu...Cu = 2.6982 (4) Å] bridged by four benzoate ligands. Each of the Cu atoms in this bunuclear copper(II) acetate hydrate analogue is present in an approximately square‐pyramidal environment, with four O atoms in a plane and the pyridine N atom at the apical site. Selected geometric parameters are compared with values for related tetrabenzoate complexes of copper(II). 相似文献
90.
Rongala Ramalakshmi Koushik Saha Dipak Kumar Roy Dr. Babu Varghese Prof. Ashwini K. Phukan Prof. Sundargopal Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17191-17195
A series of agostic σ‐borane/borate complexes have been synthesized and structurally characterized from simple borane adducts. A room‐temperature reaction of [Cp*Mo(CO)3Me], 1 with Li[BH3(EPh)] (Cp*=pentamethylcyclopentadienyl, E=S, Se, Te) yielded hydroborate complexes [Cp*Mo(CO)2(μ‐H)BH2EPh] in good yields. With 2‐mercapto‐benzothiazole, an N,S‐carbene‐anchored σ‐borate complex [Cp*Mo(CO)2BH3(1‐benzothiazol‐2‐ylidene)] ( 5 ) was isolated. Further, a transmetalation of the B‐agostic ruthenium complex [Cp*Ru(μ‐H)BHL2] ( 6 , L=C7H4NS2) with [Mn2(CO)10] affords a new B‐agostic complex, [Mn(CO)3(μ‐H)BHL2] ( 7 ) with the same structural motif in which the central metal is replaced by an isolobal and isoelectronic [Mn(CO)3] unit. Natural‐bond‐orbital analyses of 5–7 indicate significant delocalization of the electron density from the filled σB?H orbital to the vacant metal orbital. 相似文献