Structure of tetrafluoro-p-benzoquinone (p-fluoranil) at 120 K

Synthesis and characterisation of 1,2-difluoro-1,2-bis(5-trimethylsilyl-2-thienyl)ethenes. A new family of conjugated monomers for oxidative polymerisation

“…21, 22 Accordingly the bond lengths in the crystal structure of 14b are expected to be accurate. The C(1)-C(1)Ј bond measures 1.341(3) Å and is at the upper end of values found in (E ) and (Z)-difluoro substituted, alternated double bonds: for tetrafluoro-p-benzoquinone (at 113 K) a value of 1.339(2) Å was reported, 23 1.333(2) and 1.307 (9) for potassium hydrogen difluorofumarate (at 123 K) and maleate (at rt) respectively, 24 while values between 1.329(5) and 1.315(3) Å, depending essentially on the degree of conjugation and the deviations from planarity, have been reported at rt for two α,ωdiarylperfluoropolyenes. 25,26 Electron diffraction studies 27 of (E )-and (Z)-difluoroethenes give C᎐ ᎐ C double bond values of 1.331(4) and 1.329(4) Å, to be compared with 1.331(1) and 1.311(3) Å for monofluoroethene and tetrafluoroethene.…”

“…In 14b the length of the C(1)-C(2) bond, adjacent to the double bond is 1.440(2) Å: it is at the lower end of values of corresponding bond lengths in conjugated 1,2 difluorinated systems. In the case of tetrafluoro-p-benzoquinone we have 1.475 (2) Å, 23 1.499(1) Å for the planar potassium hydrogen difluoromaleate and 1.502(6) Å for the corresponding non-planar fumarate. 24 Values between 1.455(3) and 1.431(5) Å, depending upon the degree of conjugation and the deviations from planarity are found in the two cited α,ω-diarylperfluoropolyenes.…”

“…19 F decoupling) 0.36 (18H, s, -SiMe 3 ), 7 23. (2H, d, J 4,3 3.7, Th(4)-H), 7.44 (2H, d, J 3,4 3.7, Th(3)-H); δ H (500 MHz; CDCl 3 ) 0.36 (18H, s, -SiMe 3 ), 7.23 (2H, m, J 4,3 3.7, J 4,F 1.8, Th(4)-H), 7.44 (2H, d, J 3,4 3.7, Th(3)-H); δ F (500 MHz; CDCl 3 ; 1 H broad decoupling) Ϫ145.1 (2F, s); δ C (250 MHz; CDCl 3 ) 0.46 (6C, s, Th(5)SiMe 3 ), 127.0 (2C, t, J C,F1 3.7, J C,F2 3.7), 134.8 (2C, s), 136.6 (2C, t, J C,F1 9.2, J C,F2 9.2), 143.4 (2C, t, J C,F1 3.7, J C,F2 3.7), 144.7 (2C, dd, J C,F1 275.5, J C,F2 92.5, = CF); ν max /cm Ϫ1 (FTIR) 2953 (CH 3 ), 1515s, 1252vs, 1029s, 1118s (CF), 1061s (ring CH), 988vs, 839vs (ring CH), 811vs (ring CH), 758s, 538s; ν max /cm Ϫ1 (FT-Raman) 1653vs (vinyl C᎐ ᎐ C), 1422vs R mode).…”

Role of Exact Exchange and Relativistic Approximations in Calculating 19F Magnetic Shielding in Solids Using a Cluster Ansatz

“…Calculations were carried out on structures derived from single-crystal X-ray diffraction studies, with further refinements of atomic positions from plane-wave DFT geometry optimizations, as obtained in previous work . The materials in this study were 1,3,5-trifluorobenzene, , perfluorobenzene, , perfluoronaphthalene, , 2-fluorobenzoic acid, , 4-fluorobenzoic acid, , 2-fluorotoluene, , 3-fluorotoluene, , 4-fluorotoluene, , p -fluoranil, , and CFCl 3 . , The 19 F magnetic-shielding tensors of these materials were calculated on clusters of molecules, each of which represents a local portion of the extended lattice environment. The molecules selected for inclusion in the cluster were determined by the symmetry-adapted-cluster (SAC) ansatz . , The accuracy of this cluster approximation has been previously rigorously benchmarked, and its use is known to yield excellent agreement with calculations employing periodic-boundary conditions, such as those obtained using GIPAW. , In all calculations, a basis-set-partitioning scheme was used, in which the central molecule of the cluster (containing the NMR-active 19 F sites) was given the large basis set TZ2P and all other molecules were given the smaller basis set DZ.…”

π-Donor Substituent Effects on Calculated Structures, Spin Properties, and Vibrations of Radical Anions ofp-Chloranil,p-Fluoranil, andp-Benzoquinone

“…p -Benzoquinones find extensive use as electron acceptors in synthetic electron-transfer assemblies , and charge-transfer salts. − They are also ubiquitous in biological electron transfer. − Plastoquinones and ubiquinones, for example, are substituted p -benzoquinones that function as electron acceptors for energy storage in the photosynthetic reaction center 9 and energy utilization in mitochondria. , Moreover, the radical anions of p -benzoquinones (see 1 for the neutral molecules) p -benzosemiquinones (see 2 )are increasingly used in fundamental studies of ion pairing in solution , and spin densities inferred from electron paramagnetic resonance (EPR) experiments. , Although the p -benzoquinones are relatively well characterized, − their corresponding radical anions, in general, are not. This contribution presents and compares calculated structures, electronic spin density distributions, and harmonic vibrational frequencies for the radical anions of p -benzoquinone ( 2a ), p -fluoranil ( 2b ), and p -chloranil ( 2c ).…”