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CF Bond (cf + bond)
Selected AbstractsMulticyclic polyethers by the polycondensation of 1,2- or 1,3-dicyanotetrafluorobenzene with flexible diphenolsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006Hans R. Kricheldorf Abstract 1,2-Dicyanotetrafluorobenzene (1,2-DCTB) was polycondensed with various flexible diphenols in a molar ratio of 1:2, and experimental parameters such as the concentration and temperature were varied. Certain diphenols allowed a complete substitution of all CF bonds, so perfect multicyclic polyethers (BnCN, where B stands for bridge units, C represents cycles, and N is the degree of polymerization) were the main reaction products. Despite complete conversion, gelation was avoidable under optimized reaction conditions. However, in the case of 1,3-dicyanotetrafluorobenzene (1,3-DCTB), complete tetrasubstitution was not feasible with a feed ratio of 1:2. Yet, because of the inductive and mesomeric electronic interactions of all substituents in 1,3-DCTB, the three CF groups in the ortho position with respect to the cyano groups were significantly more reactive than the fourth CF bond. Therefore, polycondensations with diphenols in a 3:2 feed ratio showed a relatively clean course, yielding soluble multicycles of structure Bn /2CN. All the multicyclic polyethers were amorphous and possessed molar mass distributions with polydispersities greater than 2. Heating with Cu2+ salts caused crosslinking of the multicycles derived from 1,2-DCTB because of the formation of phthalocyanine complexes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5546,5556, 2006 [source] Computation and analysis of 19F substituent chemical shifts of some bridgehead-substituted polycyclic alkyl fluoridesMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003William Adcock Abstract The 19F NMR shieldings for several remotely substituted rigid polycyclic alkyl fluorides with common sets of substituents covering a wide range of electronic effects were calculated using the DFT-GIAO theoretical model. The level of theory, B3LYP/6,311+G(2d,p), was chosen based on trial calculations which gave good agreement with experimental values where known. The optimized geometries were used to obtain various molecular parameters (fluorine natural charges, electron occupancies on fluorine of lone pairs and of the CF bond, and hybridization states) by means of natural bond orbital (NBO) analysis which could help in understanding electronic transmission mechanisms underlying 19F substituent chemical shifts (SCS) in these systems. Linear regression analysis was employed to explore the relationship between the calculated 19F SCS and polar substituent constants and also the NBO derived molecular parameters. The 19F SCS are best described by an electronegativity parameter. The most pertinent molecular parameters appear to be the occupation number of the NBO p-type fluorine lone pair and the occupation number of the CF antibonding orbital. This trend suggests that in these types of rigid saturated systems hyperconjugative interactions play a key role in determining the 19F SCS. Electrostatic field effects appear to be relatively unimportant. Copyright © 2003 John Wiley & Sons, Ltd. [source] Bacterial hydrolytic dehalogenases and related enzymes: Occurrences, reaction mechanisms, and applicationsTHE CHEMICAL RECORD, Issue 2 2008Tatsuo Kurihara Abstract Dehalogenases catalyze the cleavage of the carbon,halogen bond of organohalogen compounds. They have been attracting a great deal of attention partly because of their potential applications in the chemical industry and bioremediation. In this personal account, we describe occurrences, reaction mechanisms, and applications of bacterial hydrolytic dehalogenases and related enzymes, particularly L -2-haloacid dehalogenase, DL -2-haloacid dehalogenase, fluoroacetate dehalogenase, and 2-haloacrylate reductase. L -2-Haloacid dehalogenase is a representative enzyme of the haloacid dehalogenase (HAD) superfamily, which includes the P-type ATPases and other hydrolases. Structural and mechanistic analyses of this enzyme have yielded important insights into the mode of action of the HAD superfamily proteins. Fluoroacetate dehalogenase is unique in that it catalyzes the cleavage of the highly stable CF bond of a fluorinated aliphatic compound. In the reactions of L -2-haloacid dehalogenase and fluoroacetate dehalogenase, the carboxylate group of Asp performs a nucleophilic attack on the ,-carbon atom of the substrate, displacing the halogen atom. This mechanism is common to haloalkane dehalogenase and 4-chlorobenzoyl-CoA dehalogenase. DL -2-Haloacid dehalogenase is unique in that a water molecule directly attacks the substrate, displacing the halogen atom. The occurrence of 2-haloacrylate reductase was recently reported, revealing a new pathway for the degradation of unsaturated aliphatic organohalogen compounds. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 67,74; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20141 [source] Multicyclic polyethers by the polycondensation of 1,2- or 1,3-dicyanotetrafluorobenzene with flexible diphenolsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006Hans R. Kricheldorf Abstract 1,2-Dicyanotetrafluorobenzene (1,2-DCTB) was polycondensed with various flexible diphenols in a molar ratio of 1:2, and experimental parameters such as the concentration and temperature were varied. Certain diphenols allowed a complete substitution of all CF bonds, so perfect multicyclic polyethers (BnCN, where B stands for bridge units, C represents cycles, and N is the degree of polymerization) were the main reaction products. Despite complete conversion, gelation was avoidable under optimized reaction conditions. However, in the case of 1,3-dicyanotetrafluorobenzene (1,3-DCTB), complete tetrasubstitution was not feasible with a feed ratio of 1:2. Yet, because of the inductive and mesomeric electronic interactions of all substituents in 1,3-DCTB, the three CF groups in the ortho position with respect to the cyano groups were significantly more reactive than the fourth CF bond. Therefore, polycondensations with diphenols in a 3:2 feed ratio showed a relatively clean course, yielding soluble multicycles of structure Bn /2CN. All the multicyclic polyethers were amorphous and possessed molar mass distributions with polydispersities greater than 2. Heating with Cu2+ salts caused crosslinking of the multicycles derived from 1,2-DCTB because of the formation of phthalocyanine complexes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5546,5556, 2006 [source] | ||||||||||