A multinuclear NMR study of the cycloaddition reaction of SNSAsF6 with tert-butylphosphaacetyline (CH3)3CCP leading to the 5-tert-butyl-1,3,2,4-dithiazaphospholium cation; a preliminary account of the novel exchange of a cyclic phosphorus by nitrogen in the reaction of with azide N3− leading to 5-tert-butyl-1,3,2,4-dithiadiazolyl

1995 ◽  
Vol 73 (8) ◽  
pp. 1312-1320 ◽  
Author(s):  
Simon Parsons ◽  
Jack Passmore ◽  
Xiaoping Sun ◽  
Manfred Regitz
Keyword(s):  
Sulfur Dioxide ◽  
Low Temperature ◽  
Cycloaddition Reaction ◽  
The Novel ◽  
Multinuclear Nmr ◽  
Tert Butyl ◽  
Nmr Study ◽  
Preliminary Account ◽  
Net Replacement

The cycloaddition reaction of SNS+ (as the AsF6− salt) with 5-tert-butylphosphaacetyline (CH3)3CCP in sulfur dioxide solution at −60 °C gave [Formula: see text], the first identified example of a 1,3,2,4-dithiazaphospholium heterocycle [Formula: see text]. The cycloadduct was characterized by multinuclear NMR (1H, 13C, 14N, 15N, 31P) spectroscopy at low temperature. Reduction of 6π [Formula: see text] in situ with SbPh3 in the presence of Me4NCl led to a radical, which may be the 7π tert-butyl-1,3,2,4-dithiazaphospholyl [Formula: see text]. The reaction of 5-tert-butyl-1,3,2,4-dithiazaphospholium [Formula: see text] with azide N3− surprisingly gave the previously known 5-tert-butyl-1,3,2,4-dithiadiazolyl [Formula: see text]. The conversion of [Formula: see text] to [Formula: see text] by the net replacement of a cyclic phosphorus with nitrogen is unprecedented. Keywords: dithiazaphospholium, dithiazaphospholyl, cycloaddition, multinuclear NMR, ESR.

In Situ High Temperature Multinuclear NMR Study of Clinker Formation

1998 ◽  
pp. 47-55
Author(s):  
Laurent Bonafous ◽  
Catherine Bessada ◽  
Dominique Massiot ◽  
Jean-Pierre Coutures ◽  
Bruno LeRolland ◽  
...  
Keyword(s):  
High Temperature ◽  
Multinuclear Nmr ◽  
Nmr Study

Dynamisches Verhalten dimerer 1,3,2,4λ2-Diazasilastannetidine und -plumbetidine in Lösung — eine Multikern-NMR-Studie/Dynamic Behaviour of Dimeric 1,2,3,4λ2-Diazasilastannetidines and -plumbetidines in Solution — a Multinuclear NMR Study

1989 ◽  
Vol 44 (3) ◽  
pp. 288-292 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Klaus Horchler ◽  
Hong Zhou ◽  
Michael Veith
Keyword(s):  
Low Temperature ◽  
Dynamic Process ◽  
Room Temperature ◽  
Dynamic Behaviour ◽  
The Other ◽  
Multinuclear Nmr ◽  
Nmr Data ◽  
Nmr Study ◽  
Intramolecular Process

1,3-Diisopropyl-2,2-dimethyl-1,3,2,4λ2-diazasilastannetidine (1b) and -plumbetidine (2b) are dimeric [(1b)2, (2b)2] in solution. At room temperature the structure of (1b)2 is fluxional. The dynamic behaviour is interpreted - on the basis of 1H. 13C, 29Si and 119Sn NMR data - as an intramolecular process in which the four-membered rings keep their identity. Such a process involves either concerted opening of the two coordinative Sn - N bonds and mutual slippage of the two rings, or consecutive cleavage of one of the coordinative Sn - N bonds and rotation about the other one. At room temperature the dimer (2b)2 is in equilibrium with its monomer 2b, whereas at low temperature the dynamic process corresponds to that established for (1b)2. In solutions which contain a mixture of the dimers (1b)2 and (2b)2, the presence of the mixed dimer 1b/2b can be proved unambiguously by consistent 29Si, 119Sn and 207Pb NMR data.

Mécanisme de la réaction de glycosylation par réversion acide en présence d'anhydride trifluorométhane sulfonique comme agent de condensation

1981 ◽  
Vol 59 (2) ◽  
pp. 482-489 ◽  
Author(s):  
André A. Pavia ◽  
Sak N. Ung-Chhun
Keyword(s):  
Low Temperature ◽  
Necessary Conditions ◽  
Free Acid ◽  
Trifluoromethanesulfonic Acid ◽  
Nmr Study ◽  
Trifluoromethanesulfonic Anhydride ◽  
Glycosylation Reaction ◽  
Comme Agent ◽  
Mechanism Of The Reaction

The acid-catalysed mechanism of the reaction using trifluoromethanesulfonic anhydride to synthesize symmetrical 1,1′-glycosyl-glycosides such as trehalose and galacto, manno, arabino, xylo etc. analogues has been elucidated. The authors were able to prove by 19F nmr study at low temperature that the efficiency of the system is due to the peculiar property of trifluoromethanesulfonic acid generated in situ to form a stable, insoluble hydroxonium trifluoromethanesulfonate CF3SO3− H3O+. The procedure satisfies the two necessary conditions for a glycosylation reaction being workable: (i) the presence in catalytic amounts of free acid which is regenerated during the condensation step; (ii) a very efficient trapping of the water liberated during the protonation step which displaces the equilibrium towards the formation of the glycoside. The α-stereoselectivity of the reaction is discussed in terms of anomerisation of the β-anomers on to the thermodynamically more stable α ones, through a cyclic oxonium intermediate.

Low Temperature Multinuclear NMR Study of the Mechanism of Protonation of W(H)2Cl2(PMe2Ph)4

1995 ◽  
Vol 34 (11) ◽  
pp. 2894-2901 ◽  
Author(s):  
Helmut Rothfuss ◽  
Dmitry G. Gusev ◽  
Kenneth G. Caulton
Keyword(s):  
Low Temperature ◽  
Multinuclear Nmr ◽  
Nmr Study

In situ generation of nitrile oxides from copper carbene and tert-butyl nitrite: synthesis of fully substituted isoxazoles

2018 ◽  
Vol 16 (25) ◽  
pp. 4683-4687 ◽  
Author(s):  
Rongxiang Chen ◽  
Abosede Adejoke Ogunlana ◽  
Shangwen Fang ◽  
Wenhao Long ◽  
Hongmei Sun ◽  
...  
Keyword(s):  
Cycloaddition Reaction ◽  
Nitrile Oxides ◽  
Tert Butyl ◽  
Keto Esters ◽  
In Situ Generation

Herein, a novel [3 + 2] cycloaddition reaction of β-keto esters with nitrile oxides, which were generated in situ from copper carbene and tert-butyl nitrite, was developed effectively to give fully substituted isoxazoles.

Hybrid polymer/nanocrystalline TiO2 composites prepared via low-temperature in-matrix crystallization of titania

e-Polymers ◽  
2010 ◽  
Vol 10 (1) ◽  
Author(s):  
Alexander Tolstov ◽  
Vitaliy Matyushov ◽  
Dmytro Klymchuk
Keyword(s):  
Low Temperature ◽  
Polymer Composites ◽  
Chemical Interaction ◽  
Sol Gel ◽  
Urethane Acrylate ◽  
The Novel ◽  
Nanocrystalline Tio2 ◽  
Novel Approach ◽  
Photoactive Materials

AbstractThe novel approach for in situ preparation of polymer/TiO2 composites via low-temperature in-matrix crystallization of sol-gel prepared titania was developed and successfully applied. Rigid aromatic polyimide (PI) and flexible poly(ether-urethane)acrylate (PEUA) were used as polymer matrices and the templates for titania crystallization. Structure and morphology of prepared hybrids have been characterized by WAXD, FTIR and SEM. Chemical interaction between functional groups of the polymers and reactive inorganic component were studied. It was found that the rigid PI is more perspective matrix (instead of flexible PEUA) for carrying out the low-temperature crystallization of TiO2. Developed crystallization technique allowed to decrease the temperature of TiO2 crystallization from 350-500 °C to 250 °C (at atmosphere pressure) and to prepare functional crystalline TiO2-based polymer composites as perspective photoactive materials. Moreover, proposed approach gives also the possibility to obtain the polymer composites with enhanced compatibility between dispersed titania and continuous polymer phases.

In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

1975 ◽  
Vol 33 ◽  
pp. 58-59
Author(s):  
F. H. Louchet ◽  
L. P. Kubin
Keyword(s):  
Electron Microscope ◽  
Transition Temperature ◽  
Low Temperature ◽  
Slip System ◽  
Low Temperatures ◽  
Tensile Axis ◽  
Image Intensifier ◽  
Screw Dislocations ◽  
Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

Role of boundaries in the crystallization of amorphous films

1988 ◽  
Vol 46 ◽  
pp. 626-627
Author(s):  
D. A. Smith
Keyword(s):  
Low Temperature ◽  
Amorphous State ◽  
Nucleation And Growth ◽  
Amorphous Films ◽  
Island Nucleation ◽  
Surface Steps ◽  
Transmission Electron ◽  
Component Systems ◽  
Temperature Deposition

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.

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