Halogenated Benzene Cation Radicals

Abstract

The halogenated benzenes C(6)HF(5), 2,4,6-C(6)H(3)F(3), 2,3,5,6-C(6)H(2)F(4), C(6)F(6), C(6)Cl(6), C(6)Br(6), and C(6)I(6) were converted into their corresponding cation radicals by using various strong oxidants. The cation-radical salts were isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy and by single-crystal X-ray diffraction. The thermal stability of the cation radicals increased with decreasing hydrogen content. As expected, the cation radicals [C(6)HF(5)](+) and 2,3,5,6-[C(6)H(2)F(4)](+) had structures with the same geometry as C(6)HF(5) and 2,3,5,6-[C(6)H(2)F(4)]. In contrast, the cation radicals [C(6)F(6)](+), [C(6)Cl(6)](+), and possibly also [C(6)Br(6)](+) exhibited Jahn-Teller-distorted geometries in the crystalline state. In the case of C(6)F(6)(+)Sb(2)F(11)(-), two low-symmetry geometries were observed in the same crystal. Interestingly, the structures of the cation radicals 2,4,6-[C(6)H(3)F(3)](+) and C(6)I(6)(+) did not exhibit Jahn-Teller distortions. DFT calculations showed that the explanation for the lack of distortion of these cations from the D(3h) or D(6h) symmetry of the neutral benzene precursor was different for 2,4,6-[C(6)H(3)F(3)](+) than for [C(6)I(6)](+).

5-Fluorolysine as alternative substrate of lysine 5,6-aminomutase: A computational study

“…For instance, B3LYP/6-311+G(d,p) calculated values were in satisfactory agreement with experimental values in the case of halogenated benzene radicals [56]. The …”

“…Accurate theoretical prediction for the 19 F HFCCs values seems difficult. Authors have employed several combinations of methods and basis sets to calculate 19 F HFCCs [56][57][58]. Nevertheless, it is yet not well established which method and basis sets predict accurate 19 F HFCCs.…”

Oxidation Chemistry of Inorganic Benzene Complexes

“…The use of weakly coordinating anions (WCA) to stabilize reactive p ‐block cations has gained enormous attention, and numerous representative examples have recently been reviewed by Krossing et al . The pioneering work of Seppelt et al in this field gave access to the single‐electron oxidation products of substituted benzenes (C 6 X 6 , X=F, Cl, Br, I) . Although C 6 I 6 shows no distortion of the initial D 6 h symmetry upon oxidation, the lighter congeners show either a quinoid (C 6 Br 6 , C 6 F 6 ) or a bisallylic (C 6 Cl 6 , C 6 F 6 ) Jahn–Teller distortion (see Scheme ).…”

“…The quinoid or bisallylic distortion of the oxidized cyclo ‐E 6 ligands of 2 a – 3 are also well comparable to the halogenated benzenes (cf. Scheme ) . Geometry optimization of the complexes [(Cp R Mo) 2 E 6 ] + ( 2 a , 2 b , 3 ) by DFT calculations results persistently in bisallylic distortions of the central cyclo ‐E 6 ligands.…”

13C‐Detected Through‐Bond Correlation Experiments for Protein Resonance Assignment by Ultra‐Fast MAS Solid‐State NMR

“…[C 6 F 6 ] + was possibly the first one that could be isolated, but a structure determination was missing 3,4. Only recently, the first of such structure determinations became available, for [C 6 F 6 ] + ,5 [C 6 F 5 H] + ,6 1,2,4,5‐[C 6 F 4 H 2 ] + ,6 1,3,5‐[C 6 F 3 H 3 ] + ,6 [C 6 Cl 6 ] + ,6 and [C 6 I 6 ] + 6. Simultaneously, the crystal structure of [1,4‐(CH 3 O) 2 ‐2,5‐F 2 C 6 H 2 ] + [Nb 2 F 11 ] – was reported 7…”