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Chlorine Substituents (chlorine + substituent)
Selected AbstractsThe Effects of Fluorine and Chlorine Substituents across the Fjords of Bifluorenylidenes: Overcrowding and StereochemistryEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2006Sergey Pogodin Abstract The bistricyclic aromatic enes (BAEs) (E)- and (Z)-1,1,-difluorobifluorenylidene, 1,8,1,,8,-tetrafluorobifluorenylidene, (E)- and (Z)-3,3,-difluorobifluorenylidene, 3,6,3,,6,-tetrafluorobifluorenylidene, and their chlorinated analogues were subjected to a DFT study of overcrowding in their fjord regions. The B3LYP hybrid functional was employed to calculate energies and geometries of the twisted conformations of these BAEs. The diastereomers E11,F2 and Z11,F2 have identical twist angles (, = 37.1°) and similar degrees of overcrowding, but differ in the degree and mode of pyramidalization, ,. In E11,F2, ,(C9) = +,(C9,) = 7.0° (syn -pyramidalization), while in Z11,F2, ,(C9) = ,,(C9,) = 1.0° (anti -pyramidalization). By contrast, in E11,Cl2 and Z11,Cl2, , = 40.6° and 42.7°, respectively. Introducing four halogen substituents results in higher twist angles: , = 40.3° in 181,8,F4 and 52.6° in 181,8,Cl4. Surprisingly, Z11,F2 is more stable than E11,F2 (,H298 = ,1.9 kJ/mol), whereas Z11,Cl2 is less stable than E11,Cl2 (,H298 = 2.2 kJ/mol). Both results are consistent with the experimental relative stabilities of these diastereomers. The unexpected stability of Z11,F2 is explained by a combination of steric and electronic effects. Calculations of Coulomb energies for point charge systems of atoms C, F, and H in the fjord regions shows stabilization of the (Z) diastereomer by ,45.5 kJ/mol. The dipole,dipole interactions in the fjord region destabilize Z11,F2 by 6.4 kJ/mol relative to E11,F2. Careful examination of the NMR spectra of E11,F2 and Z11,F2 shows, in the latter, evidence of long-range fluorine,fluorine coupling over seven bonds (11.4 Hz) and carbon,fluorine coupling over six bonds (4.8 Hz).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Gas-phase hydrodechlorination of chlorobenzenes over silica-supported palladium and palladium,ytterbium,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6-7 2003Satyakrishna Jujjuri Abstract A 5% w/w palladium loading on silica has been achieved via impregnation of the support with Pd(C2H3O2)2 and { (DMF)10Yb2[Pd(CN)4]3} , precursors to deliver monometallic (Pd/SiO2) and bimetallic (Yb,Pd/SiO2) catalyst systems respectively. The catalytic action of each has been assessed in the continuous gas-phase hydrodechlorination (HDC) of chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB) (T = 423 K, inlet chlorine/palladium mol ratio of 5 × 103 h,1) and the hydrogenation of benzene (T = 423 K, inlet C6H6/palladium mol ratio of 35 h,1). Activation of both catalysts delivered similar palladium crystallite size distributions with an average palladium diameter of 5,6 nm where the ytterbium component (in Yb,Pd/SiO2) was present as a thin surface coating. The Pd,Yb bimetallic exhibited significantly higher HDC and hydrogenation activities, the former manifested by significantly greater fractional dechlorinations and benzene selectivities/yields. Yb/SiO2 proved inactive in terms of promoting hydrogen scission or addition and the promotional effect of ytterbium in Yb,Pd/SiO2 is discussed in terms of electron donation and hydrogen transfer via surface YbH2. Under identical reaction conditions, a lower HDC activity was recorded for 1,2-DCB compared with CB, a response that is attributed to steric constraints allied to the deactivating effect of the second chlorine substituent. Both Pd/SiO2 and Yb,Pd/SiO2 exhibited a decline in HDC activity with time-on-stream, but the bimetallic was significantly more resistant to deactivation. Copyright © 2003 John Wiley & Sons, Ltd. [source] High-Performance Air-Stable n-Type Organic Transistors Based on Core-Chlorinated Naphthalene Tetracarboxylic DiimidesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Joon Hak Oh Abstract Core-chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are synthesized and employed for n-channel organic thin-film transistors (OTFTs). Structural analyses of the single crystals and thin films are performed and their charge-transport behavior is investigated in terms of structure,property relationships. NDIs with two chlorine substituents are shown to exhibit a herringbone structure with a very close ,-plane distance (3.3,3.4,Ĺ), a large ,-stack overlap (slipping angle ca. 62°), and high crystal densities (2.046,2.091,g,cm,3). These features result in excellent field-effect mobilities of up to 1.43,cm2,V,1,s,1 with minimal hysteresis and high on,off ratios (ca. 107) in air. This is similar to the highest n-channel mobilities in air reported so far. Despite the repulsive interactions of bulky Cl substituents, tetrachlorinated NDIs adopt a slip-stacked face-to-face packing with an interplanar distance of around 3.4,Ĺ, resulting in a high mobility (up to 0.44,cm2,V,1,s,1). The air-stability of dichlorinated NDIs is superior to that of tetrachlorinated NDIs, despite of their higher LUMO levels. This is closely related to the denser packing of the fluorocarbon chains of dichlorinated NDIs, which serves as a kinetic barrier to the diffusion of ambient oxidants. Interestingly, these NDIs show an optimal performance either on bare SiO2 or on octadecyltrimethoxysilane (OTS)-treated SiO2, depending on the carbon number of the fluoroalkyl chains. Their synthetic simplicity and processing versatility combined with their high performance make these semiconductors highly promising for practical applications in flexible electronics. [source] Additive Tuning of Redox Potential in Metallacarboranes by Sequential Halogen SubstitutionCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2010Patricia González-Cardoso Abstract The first artificially made set of electron acceptors is presented that are derived from a unique platform Cs[3,3,-Co(C2B9H11)2], for which the redox potential of each differs from its predecessor by a fixed amount. The sequence of electron acceptors is made by substituting one, two, or more hydrogen atoms by chlorine atoms, yielding Cs[3,3,-Co(C2B9H11,yCly)(C2B9H11,zClz)]. The higher the number of chlorine substituents, the more prone the platform is to be reduced. The effect is completely additive, so if a single substitution implies a reduction of 0.1,V of the redox potential of the parent complex, then ten substitutions imply a reduction of 1,V. [source] | ||||||||||