Search results for "Halogen"

New insight into halogen release from experimental studies on BrO/Br ratios in volcanic plumes

2014

Phytoscreening as an efficient tool to delineate chlorinated solvent sources at a chlor-alkali facility

2017

Chlorinated ethenes (CE) are among the most common volatile organic compounds (VOC) that contaminate groundwater, currently representing a major source of pollution worldwide. Phytoscreening has been developed and employed through different applications at numerous sites, where it was generally useful for detection of subsurface chlorinated solvents. We aimed at delineating subsurface CE contamination at a chlor-alkali facility using tree core data that we compared with soil data. For this investigation a total of 170 trees from experimental zones was sampled and analyzed for perchloroethene (PCE) and trichloroethene (TCE) concentrations, measured by solid phase microextraction gas chromato…

Atom transfer radical polymerization with different halides (F, Cl, Br, and I): Is the process "living" in the presence of fluorinated initiators?

2016

Atom transfer radical polymerization (ATRP) is often used for grafting from fluorinated polymers. Nevertheless, the possibility to initiate an ATRP from a C-F functionality and the activity of the catalysts in the presence of fluoride anions are essentially unexplored. Therefore, we investigated the thermodynamics and kinetics of C-F bond activation by ATRP catalysts and compared it with other halide systems. The ATRP equilibrium constant was estimated to be small for the reaction between [CuITPMA]+ and benzyl fluoride (TPMA = tris(2-pyridylmethyl)- amine). However, [CuITPMA] + could react with the more active initiator diethyl fluoromalonate (DEFM). With DEFM as initiator and CuIBr/TPMA as…

Surface-relief gratings in halogen-bonded polymer-azobenzene complexes A concentration-dependence study

2017

In recent years, supramolecular complexes comprising a poly(4-vinylpyridine) backbone and azobenzene-based halogen bond donors have emerged as a promising class of materials for the inscription of light-induced surface-relief gratings (SRGs). The studies up to date have focused on building supramolecular hierarchies, i.e., optimizing the polymer–azobenzene noncovalent interaction for efficient surface patterning. They have been conducted using systems with relatively low azobenzene content, and little is known about the concentration dependence of SRG formation in halogen-bonded polymer–azobenzene complexes. Herein, we bridge this gap, and study the concentration dependence of SRG formation…

Oxidative Addition of Halogens on Open Metal Sites in a Microporous Spin-Crossover Coordination Polymer

2009

One-Pot Synthesis of Pyrrole-2-carboxylates and -carboxamides via an Electrocyclization/Oxidation Sequence

2014

An electrocyclic ring closure is the key step of an efficient one-pot method for the synthesis of pyrrole-2-carboxylates and -carboxamides from chalcones and glycine esters or amides. The 3,4-dihydro-2H-pyrrole intermediates generated in situ are oxidized to the corresponding pyrroles by stoichiometric oxidants or by catalytic copper(II) and air in moderate to high yields. A wide range of functional groups are tolerated, and further combination with an in situ bromination gives access to polyfunctional pyrrole scaffolds.

Synthesis of Densely Functionalised 5-Halogen-1,3-oxazin-2-ones byHalogen-Mediated Regioselective Cyclisation of N-Cbz-ProtectedPropargylic Amines: A…

2013

A very efficient synthesis of 5-halogen-1,3-oxazin-2-ones has been accomplished by the halocyclisation reaction of chiral nonracemic N-carbobenzyloxy (N-Cbz)-protected propargylic amines by using I-2, Br-2 and Cl-2 as electrophile sources. The nature of the halogen influences the reaction time and yield. However, in all cases the reaction is totally regioselective taking place through a 6-endo-dig process regardless of the nature of the halogen and of the substituents in the starting material. To rationalise the experimental results, theoretical studies at the B3LYP/6-311G* level have been performed.

Prediction of new inorganic molecules with quantum chemical methods

2006

Quantum chemistry can today be employed to invent new molecules and explore unknown molecular bonding. An overview of novel species containing metals bound to polynitrogen clusters is presented. The prediction of metal polyhydrides is discussed. Finally, some species containing gold that behaves as a halogen are described, together with recent advances in actinide chemistry and exploration of the nature of the actinide–actinide chemical bonding.

Study of the MAu6(M = Cr, Mo, W) molecular species: A transition from halogenlike to hydrogenlike chemical behavior for gold

2004

Quantum chemical calculations suggest that a series of molecules with the general formula MAu6 are stable, where M is a a group 6 atom, Cr, Mo, W, respectively. These species have a structure analogous to the corresponding MH6 compounds, while they differ from the MX6, where X is a halogen. The further reaction MAu6 + 3Au2 → MAu12 is strongly exothermic.

Supramolecular hierarchy among halogen and hydrogen bond donors in light-induced surface patterning

2015

Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an io…