Search results for "SUBSTITUTION"

Kinetics and Mechanism of the Nucleophilic Substitution of Tellurium(II) Dialkanethiolates, Te(SR1)2 with Thiols, HSR2

2005

The equilibrium reaction between tellurium(II) dithiolates and thiols, Te(SR1)2 + 2 HSR2 ⇌ Te(SR2)2 + 2 HSR1 was studied by means of 1H- and 125Te NMR spectroscopy and ab initio quantum chemical methods. It was found that the reaction is catalyzed by Bronsted acids and bases, the catalytic activity corresponding to the strength of the respective acid or base. Investigation of the initial step of the reaction, Te(SR1)2 + HSR2 ⇌ Te(SR1)(SR2) + HSR1, showed it to proceed according to first order kinetics for Te(SR1)2, HSR2 and for the catalyst. Ab initio geometry optimizations and frequency calculations suggest [Te(SR1)(HSR1)(HSR2)]+ and [Te(SR1)2(SR2)]− to be stable intermediates and not tran…

Electrochemical and chemical reduction of niobocene dichlorides in the presence of carbon dioxide

1995

Abstract The chemical and electrochemical reduction of the niobocene dichlorides [Nb(η5-C5H4SiMe3)2Cl2]1, [Nb(η5-C5Me5)2Cl2] 2 and [Nb(η5-C5Me4Et)2Cl2] 3, in the presence of carbon dioxide has been investigated. Formation of compounds of the type [Cp2Nb(CO2)] and [Cp2(∗)NbCl(CO2))] 1 has been established by means of IR, ESR and/or NMR spectroscopy. They contain a labile η2-CO2. The order of stability increases with the degree of substitution the Cp. Less stable intermediates in the reduction of the system [Cp2NbCl2]/CO2 are discussed on the basis of cyclovoltammetric and coulometric data.

Modular Phosphole-Methano-Bridged-Phosphine(Borane) Ligands. Application to Rhodium-Catalyzed Reactions

2012

The synthesis of the phospholyl(phosphinoborane)methane air- and moisture-stable hybrid ligands 4a–f, starting from 1-phenylphospholes 1a–d, was performed via P–C bond coupling on the methano bridge. Two strategies were investigated, according to the phospholyl moiety used as a nucleophilic or an electrophilic reagent. In the first pathway, the phospholyl anions react with the easily available (chloromethyl)diphenylphosphine–borane 3 to afford ligands 4a–d in 29–67% isolated yields. In the second pathway, the phospholyl(dicyclohexylphosphinoborane)methane ligands 4e,f were synthesized in 18–23% yields, through a nucleophilic substitution on the cyanophosphole. Removal of the BH3 moiety on 4…

Hexasubstituted Benzenes with Ultrastrong Dipole Moments

2015

Hexasubstituted benzenes have been synthesized with the highest known dipole moments, as determined by dielectric spectroscopy and DFT methods. Based on the preparation of 4,5-diamino-3,6-dibromophthalonitrile, combined with a novel method to synthesize dihydrobenzimidazoles, these benzene derivatives have dipole moments in excess of 10 debye. Such dipole moments are desirable in ferroelectrics, nonlinear optics, and in organic photovoltaics. Structure determination was achieved through single-crystal X-ray crystallography, and the optical properties were determined by UV/Vis absorption and fluorescence spectroscopy.

Substitution of hazardous substances for health and environment: lessons and experiences from European projects

1999

This paper deals with substitution of hazardous substances in production processes for environmental and health and safety reasons, with special reference to experiences of substitution of volatile organic compounds in paints and in concrete mould release agents. Substitution in this context is seen as a particular kind of technological transfer, in which the main value of the technology lies in its environmental and health and safety performances, as a contribution to industrial sustainability. The authors identify the main actors of the substitution process (industry, trade unions, NGOs, etc.), the role they play in such a process (promoter, target group, ally or opposer) and the scene i…

Orthotopic MAINZ pouch bladder substitution – long-term follow-up

2021

Introduction After radical cystectomy, orthotopic neobladder is one surgical strategy for urinary diversion. To assess the usefulness of an operation, long-term data are essential. We examined long-term complications and continence rates of orthotopic ileocecal (MAINZ pouch) bladder substitution. Material and methods Between 1986 and 2011, 193 patients underwent orthotopic MAINZ pouch bladder substitution. Until July 2000, ureter implantation was performed into the ascending colon through a submucosal tunnel technique (Goodwin-Hohenfellner). After July 2000, ureters were implanted into the terminal Ileum using the ileocecal valve to prevent reflux: the left spatulated ureter by an end-to-en…

A rare case of peri-implant distal radius fracture☆

2021

A peri-implant fracture near the volar plate of distal radius represent a very rare injury. The main factor of this lesion is high energy trauma on the wrist. We report a case of a 61-year-old woman with a peri-implant fracture located just proximally to the plate and a fracture of the ulnar head that occurred after a simple fall. The patient was surgically treated by plate and screws removal. The fracture was fixed using a longer volar plate for the radial fracture and a plate for the head ulnar fracture. Different factors such as osteoporosis, BMI and screw position could influence the fracture pattern. However, considering growing use of plates for distal radius fracture fixation, the fr…

C172S Substitution in the Chloroplast-encoded Large Subunit Affects Stability and Stress-induced Turnover of Ribulose-1,5-bisphosphate Carboxylase/Ox…

1999

Previous work has indicated that the turnover of chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1. 39) may be controlled by the redox state of certain cysteine residues. To test this hypothesis, directed mutagenesis and chloroplast transformation were employed to create a C172S substitution in the Rubisco large subunit of the green alga Chlamydomonas reinhardtii. The C172S mutant strain was not substantially different from the wild type with respect to growth rate, and the purified mutant enzyme had a normal circular dichroism spectrum. However, the mutant enzyme was inactivated faster than the wild-type enzyme at 40 and 50 degrees C. In contrast, C172S mutant …

Independent tuning of electronic levels in pentacene by site-specific substitution.

2008

The Chemistry of [1,2,3]Triazolo[1,5- a] pyridines

2003

The reactivity of [1,2,3]triazolo[1,5-a]pyridines 1 is described. Triazolopyridines react with electrophiles in two contrasting ways, giving 3-substituted triazolopyridines 2, or products 3, resulting from triazolo ring opening with loss of molecular nitrogen. The triazolopyridines can be lithiated at -40 degrees C by lithium diisopropylamide in ether giving regiospecifically the 7-lithio derivative. Bromotriazolopyridines have activation towards nucleophilic substitution at position 5 and 7, and benzenoid inertness at position 6. The parent compound 1a is easily hydrogenated giving tetrahydrotriazolopyridine 11a in high yield; when the triazolopyridines have substituents, the hydrogenation…