Bromine Molecules (bromine + molecule)

Distribution by Scientific Domains

Selected Abstracts

Competing kinetic pathways in the bromine addition to allylic ethers in 1,2-dichloroethane: Opposite temperature effects

Alessandro Cecchi
The kinetics of the electrophilic bromination of three allylic ethers in a nonprotic solvent, 1,2-dichloroethane, has been investigated. Two of them followed a prevalent second-order pathway, while the third one exhibited a classical, clean third order. The second-order pathway in the first two olefins is attributed to electrophilic assistance of the ethereal oxygen to the attacking bromine molecule. In the molecular bromination of 2,4- cis -dimethyl-8-oxabicyclo[3.2.1]-6-octen-3- cis -ol, opposite temperature dependences were found for the two different kinetic pathways. An exoergonic process for the second-order reaction was explained by the lesser stability of the bromiranium,bromide ionic intermediate, compared to the bromiranium,tribromide in the third-order profile. 2007 Wiley Periodicals, Inc. 39: 197,203, 2007 [source]

Development of graphene layers by reduction of graphite fluoride C2F surface

A. V. Okotrub
Abstract We studied a possibility of reduction of the surface of graphite fluoride obtained by fluorination of highly oriented pyrolytic graphite (HOPG) by a gaseous mixture of BrF3 and Br2. X-ray diffraction (XRD) revealed a layered structure of the fluorinated product being a second-stage intercalate due to a presence of bromine molecules between the fluorinated graphite layers. Scanning tunneling microscopy and spectroscopy showed that the "old" surface of graphite fluoride (exposed to the ambient air) has the graphite-like structure, while the fresh cleaved surface is non-conductive. Therefore, the outer layers of graphite fluoride can be reduced by water present in the laboratory atmosphere. The sample was treated by H2O vapor to confirm that. The reduction was controlled by Raman spectroscopy using intensity of the 1360 and 1580,cm,1 bands. The energy dependent photoelectron spectroscopy was used for estimation of thickness of the reduction layer, which was found, does not exceed 2,3 graphite layers. The obtained results indicate the possibility of synthesis of graphene layers on dielectric fluorinated graphite matrix. [source]

Photolysis of Br2 in CCl4 studied by time-resolved X-ray scattering

Qingyu Kong
A time-resolved X-ray solution scattering study of bromine molecules in CCl4 is presented as an example of how to track atomic motions in a simple chemical reaction. The structures of the photoproducts are tracked during the recombination process, geminate and non-geminate, from 100,ps to 10,s after dissociation. The relaxation of hot Br2* molecules heats the solvent. At early times, from 0.1 to 10,ns, an adiabatic temperature rise is observed, which leads to a pressure gradient that forces the sample to expand. The expansion starts after about 10,ns with the laser beam sizes used here. When thermal artefacts are removed by suitable scaling of the transient solvent response, the excited-state solute structures can be obtained with high fidelity. The analysis shows that 30% of Br2* molecules recombine directly along the X potential, 60% are trapped in the A/A, state with a lifetime of 5.5,ns, and 10% recombine non-geminately via diffusive motion in about 25,ns. The Br,Br distance distribution in the A/A, state peaks at 3.0,. [source]

Microstructure analysis of brominated styrene,butadiene rubber

Sepideh Khoee
The bromine addition to the SBR double bonds in chloroform at 0C has been investigated by FTIR, 1H NMR and DSC techniques. In this case, bromine molecules react exclusively with the polydiene double bonds and the polystyrene units are unaffected. The bromine reacts preferentially with 1,4-trans double bonds of the polybutadiene segment of SBR. At low bromination level (below 15%) the bromine reacts mainly with the 1,4-trans double bonds of SBR, while at higher bromination level (up to 30%) the bromine shows the most reactivity toward the vinylic double bond. Above 30%, the addition reaction occurs on 1,4-trans double bonds. The microstructure of modified and unmodified styrene,butadiene copolymers were fully characterized by 1H NMR technique. Expanded regions have been utilized to resolve the complex 1H NMR spectrum and establish the compositional and configurational sequences of styrene,butadiene copolymers. POLYM. ENG. SCI., 47:87,94, 2007. 2007 Society of Plastics Engineers [source]