A crystalline H-bond cluster of hexafluoroisopropanol (HFIP) and piperidine: Structure determination by X ray diffraction

Piperidine and 1,1,1-3,3,3 hexafluoro-2-propanol (HFIP) have been co-crystallized and X-ray crystal structure has been explored. Single-crystal X-ray analysis displays the existence of hydrogen bonding aggregates through dimers 1 of the complex (one piperidine/two HFIP) where the heteroatoms form a six-center ring. In this cluster 1, each heteroatom (N, O) is multiple H-bond donor and acceptor. Surprisingly the strongest H-bond of the network is where HFIP acts as an acceptor from the amine. In this complex HFIP adopts a conformation different from that of HFIP aggregates. The supramolecular architecture is also based on discrimination between polar and hydrophobic parts that allows the alignment of molecules and the formation of parallel channels. NMR experiments show that strong interactions between piperidine and HFIP are maintained in solution.     

Low-temperature F NMR spectroscopy of 1-fluoro-1-lithioethenes : Stability, shifts and unexpected coupling constants

Half-lives and fluorine atom shifts of stabilized 1-fluoro-1-lithioethenes bearing hydrogen, fluorine, phenyl, and/or dimethylphenylsilyl groups in the β-positions have been determined by a low-temperature ¹⁹F NMR spectroscopy. Some 1-fluoro-1-lithioethenes displayed an exceptionally low value of the trans-³J_FF coupling constant. Stereoselectivity of carbenoid formation, as well as an effect of configuration on the stability is discussed.     

Organofluorine compounds and fluorinating agents : Part 28. New perfluoroalkyl substituted chiral mesogens

The perfluorohexyl-aryl-thioethers 3 and 4, building blocks for the synthesis of the chiral target mesogens 12-15, were prepared by dithionite-mediated S-perfluoroalkylation of the p-substituted thiophenols 1 and 2. The phenolic HO group of 3 was O-glucosylated with pentaacetyl-d-glucopyranose to 5 followed by deacetylation forming the tetrol 6 and by acetalizing with 4-(4-perfluorohexylsulfanyl-benzoyloxy)-benzaldehyde-dimethylacetal (8) generating the dihydroxy-intermediate 9. The latter contains two perfluorohexylthio chains. Alternatively, the dimethylacetal 8 was linked to p-octylphenyl-β-d-glucopyranoside (10) giving the mixed octyl/perfluorohexyl substituted p-octylphenyl-4,6-O-[4′-(4″-perfluorohexylsulfanyl)-benzoyloxy]-benzylidene-β-d-glucopyranoside (11). Compound 8 was obtained via esterification of 4 with p-hydroxy-benzaldehyde to 4-(4-perfluorohexylsulfanyl-benzoyloxy)-benzaldehyde (7). Finally, the diols 9 and 11 were dehydroxylated to 12 and 13 followed by hydrogenation yielding 14 and 15, respectively. Tetrol 6, diols 9, 11 and the non-amphiphilic compounds 7, 12-15 are thermotropic liquid crystals.     

Environmental assessment of CFC alternatives: Rate constants for the reactions of OH radicals with fluorinated compounds

The rate constants for the reactions of OH radicals with CF₃OCHFCF₃, and CF₃CHFCF₃ have been measured over the temperature range 250-430 K. Kinetic measurements have been carried out using the flash photolysis, and laser photolysis methods combined, respectively, with the laser induced fluorescence technique. The influence of impurities in the samples has been investigated by using gas chromatography. No sizable effect of impurities was found on the measured rate constants of these fluorinated compounds, if the purified samples were used in the measurements. The following Arrhenius expressions were determined: k(CF₃OCHFCF₃) = (4.39 ± 1.38) × 10⁻¹³ exp[−(1780 ± 100)/T] cm³ molecule⁻¹ s⁻¹, and k(CF₃CHFCF₃) = (6.19 ± 2.07) × 10⁻¹³ exp[−(1830 ± 100)/T] cm³ molecule⁻¹ s⁻¹.