Structural studies, fluorinated alkyl

Another example of a trifluoromethyl heteroaryl-containing herbicide is di-thiopyr (Dimension ) [72], Structure-activity studies have demonstrated that a fluorinated alkyl group is required for optimum activity at the 2 and/or 6 positions of the pyridine ring [73], Thiazopyr (Mandate , Visor ), a herbicide related to dithiopyr, was introduced by Monsanto in 1992 and later sold to Rohm and Haas. It is used for the pre-emergence control of annual grass and a few broadleaf weeds in tree fruit, vines, sugar cane, and other crops. 

Many research groups have been systematically studied the effect of the structure-property relationship on gas transport properties of fluorinated polyimides. In this connection, Kim et al. investigated the effect of incorporating fluorinated alkyl side groups into polyimide membranes in terms of their physical and gas permeation properties (Table 3.5) [61]. They demonstrated four polyimides with fluorinated side groups and another four without side groups by polycondensation of 2-(perfluorohexyl)ethyl-3,5-diamino benzoate (PFDAB) and m-PDA with four aromatic dianhydrides (6FDA, ODPA, BTDA, and PMDA), respectively (Scheme 3.12). 

Synthetic methods have been devised that lead to moderate to good yields of a-fluorinated alkyl cobaloximes. NMR studies and structural comparisons to the nonfluorinated analogs suggest that there is a significant ionic character in the bonding of the fluorinated alkyl ligands to the cobalt center. 

In contrast, fluorinated surfactants with a predominantly fluorinated alkyl chain obey the cmc-chain length relationships expressed by Eqs. (34) and (37). Selve at al. [157] studied the surface activity of fluorinated nonionic surfactants with a two-chain polyoxyethylene hydrophilic head linked to the hydrophobe via an amide bond, F(CF2)/(CH2), C(0)N[(C2H40) CH3]2. The cmc values of surfactants with a structure m = 1, = 3, and / = 6,8, and 10 are 0.55,0.012, and 0.0003 mmol/L, respectively. The ratio of the cmc values for the surfactants with 1 = 6 and 8 is 46, which corresponds to a 1.7-fold cmc decrease per C2F4 unit. As expected, the cmc values of the fluorinated surfactant with six CF2 groups are very similar to the cmc values of a hydrocarbon surfactant with 10 CH2 groups (Table 6.10). 

Adcock, W. Abeywickrema, A. N. Substituent effects in the bicyclo[2.2.2]octane ring system. A carbon-13 and fluorine-19 nuclear magnetic resonance study of 4-substituted bicyclo[2.2.2]oct-l-yl fluorides, / Org. Chem 1982,47,2957-2966. Laube, T Ha, T. K. Detection of hyperconjugative effects in expaimentaUy dete-mined structures of neutral molecules, J. Am. Chem. Soc. 1988,110, 5511-5517. Rozeboom, M. D. Houk, K. N. Stereospecific alkyl group effects on amine lone-pair ionization potentials Photoelectron spectra of alkylpiperidines, / Am Chem Soc. 1982,104,1189-1191. 

One problem was that three different groups had to be connected regioselec-tively to the 1,2- and 3-positions of the benzene ring in the phthaloyl moiety. An iodine atom was introduced selectively into the 3-position of the phthaloyl moiety by a palladium-catalyzed reaction in the presence of a specific substituent in the 2-position. On the basis of the structure-activity relationship, the introduction of lipophilic alkyl substituents, including fluorine atoms, seemed to increase the activity though a practical method of introduction was not available. The overcoming of such difficulties led to dramatic advances in terms of a more detailed study on the structure-activity relationship as well as the establishment of a facile synthetic method that provided various new derivatives. 

These reactions have also been studied by DFT. When the set of four ruthenium isomers is considered (Scheme 51), it becomes clear that the [Ru(H)F(PH3)2(GO)(=GF2)] is almost equienergetic with [RuH(GF3)(PH3)2(GO)]. However, the fluorocarbene complex, [RuF2(PH3)2(GO)(=GFH)], is substantially more stable, and the difluoromethyl complex, [Ru(GF2H)F(PH3)2(GO)], is the most stable of all in accord with experiment. The calculated structure of [RuH(GF3)(PH3)2(GO)] shows a remarkable distortion of the GF3 group in which one fluorine is brought close to the metal (2.626 A) while extending its G-F bond (Scheme 51). This structure resembles that of an agostic alkyl, and clearly assists the a-fluorine elimination. " ... 

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