Revisiting the electrochemical formation, stability and structure of radical and biradical anionic structures in dinitrobenzenes

Intermolecular hydrogen bonding of alcohols with dinitrobenzene radical anion and dianion: A combined electrochemical and DFT study

Hydrogen bonding is one of the most important inter-molecular interactions in the field of biochemistry and medicinal chemistry. Such non-covalent interactions play a vital role in self-assembly phenomena, chemical structures, material properties and enzymatic catalysis. Herein, we present hydrogen bonding phenomenon in alcohols-dinitrobenzene (DNB) radical anion/dianion systems using electrochemical and computational approaches. First, 1,3-DNB radical anion and dianion were generated through electrochemical method and then hydrogen bonding interactions with aliphatic alcohols in DMSO are studied through cyclic voltammetry (CV). CV results show that the cathodic peak potential of 1,3-Dinitrobenzene in Dimethyl sulfoxide is shifted catholically upon addition of alcohols which represent hydrogen bonding phenomenon. Theoretical investigations are performed to gain deep insight on hydrogen bonding interaction strength in DNB-alcohol systems. H-bonding interaction of all isomers of DNB (1,2-, 1,3-, 1,4-), its corresponding radical anion, and dianion with aliphatic alcohols is studied using density functional calculations. The strength of H-bonding is evaluated both qualitatively and quantitatively using interaction energies, vibrational and electronic spectroscopic analysis. Understanding of these interactions will be helpful in gaining insight into biological systems where these interactions play significant role.

Generation of Thiyl Radicals from Air-Stable, Odorless Thiophenol Surrogates: Application to Visible-Light-Promoted C–S Cross-Coupling

The synthetic versatility of thiophenols is offset by their air-sensitivity and foul odor. It is demonstrated that S-aryl isothiouronium salts can be used as precursors to thiyl radicals, extending the practical benefits of these air-stable, odorless salts from ionic to single electron manifolds. The isothiouronium salts are accessed via Ni-catalyzed cross-coupling of (hetero)aryl iodides and thiourea and are isolated as free-flowing solids following anion exchange. Judicious choice of a redox-innocent counteranion enables use of these convenient thiophenol surrogates in radical processes, as is exemplified by the synthesis of non-symmetrical diaryl thioethers via light-promoted S-arylation.

Electrochemistry and spectroelectrochemistry of 1,4-dinitrobenzene in acetonitrile and room-temperature ionic liquids: ion-pairing effects in mixed solvents

Room-temperature ionic liquids (RTILs) have been shown to have a significant effect on the redox potentials of compounds such as 1,4-dinitrobenzene (DNB), which can be reduced in two one-electron steps. The most noticeable effect is that the two one-electron waves in acetonitrile collapsed to a single two-electron wave in a RTIL such as butylmethyl imidazolium-BF4 (BMImBF4). In order to probe this effect over a wider range of mixed-molecular-solvent/RTIL solutions, the reduction process was studied using UV-vis spectroelectrochemistry. With the use of spectroelectrochemistry, it was possible to calculate readily the difference in E°'s between the first and second electron transfer (ΔE12° = E1° - E2°) even when the two one-electron waves collapsed into a single two-electron wave. The spectra of the radical anion and dianion in BMImPF6 were obtained using evolving factor analysis (EFA). Using these spectra, the concentrations of DNB, DNB(-•), and DNB(2-) were calculated, and from these concentrations, the ΔE12° values were calculated. Significant differences were observed when the bis(trifluoromethylsulfonyl)imide (NTf2) anion replaced the PF6(-) anion, leading to an irreversible reduction of DNB in BMImNTf2. The results were consistent with the protonation of DNB(2-), most likely by an ion pair between DNB(2-) and BMIm(+), which has been proposed by Minami and Fry. The differences in reactivity between the PF6(-) and NTf2(-) ionic liquids were interpreted in terms of the tight versus loose ion pairing in RTILs. The results indicated that nanostructural domains of RTILs were present in a mixed-solvent system.

Quantum-chemical insights into mixed-valence systems: within and beyond the Robin–Day scheme

The application of quantum-chemical methods to both organic and transition-metal mixed-valence systems is reviewed, with particular emphasis on how to describe correctly delocalisation vs. localisation near the borderline between Robin–Day classes II and III.