Stereochemistry and mechanism of the copper(I) halide cleavage of thallium-carbon bonds

Stereochemical studies on the copper(I) halide cleavage of thallium-carbon bonds in acetonitrile indicate that at 80°C a radical path accounts for approximately $\text{2}\text{3}$ of the product, whereas at 60°C an ionic path predominates. The results are consistent with e.s.r. measurements by a spin trapping technique.     

Dynamics of halide ion-water hydrogen bonds in aqueous solutions: dependence on ion size and temperature

We have carried out a series of molecular dynamics simulations to investigate the dynamics of X(-)-water (X = F, Cl, Br, and I) and water-water hydrogen bonds in aqueous alkali halide solutions at room temperature and also of Cl(-)-water and water-water hydrogen bonds at seven different temperatures ranging from 238 to 318 K. The hydrogen bonds are defined by using a set of configurational criteria with respect to the anion(oxygen)-oxygen and anion(oxygen)-hydrogen distances and the anion(oxygen)-oxygen-hydrogen angle for an anion(water)-water pair. The results of the hydrogen bond dynamics are obtained for two different cutoff values for the angular criterion. In both cases, similar dynamical behavior of the hydrogen bonds is found with respect to their dependence on ion size and temperature. The fluoride ion-water hydrogen bonds are found to break at a much slower rate than water-water hydrogen bonds, while the lifetimes of chloride and bromide ion-water hydrogen bonds are found to be shorter than those of fluoride ion-water ones but still longer than water-water hydrogen bonds. The short-time dynamics of iodide ion-water hydrogen bonds is found to be slightly faster, while its long-time dynamics is found to be slightly slower than the corresponding water-water hydrogen bond dynamics. Correlations of the observed dynamics of anion(water)-water hydrogen bonds with those of rotational and translational diffusion and residence times of water molecules in ion(water) hydration shells are also discussed. With variation of temperature, the lifetimes of both Cl(-)-water and water-water hydrogen bonds are found to show Arrhenius behavior with a slightly higher activation energy for the Cl(-)-water hydrogen bonds.     

Hexahalogenotin(IV) complexes in aqueous mixed hydrogen halide solutions in the glassy state

The configurations of hexahalogenotin(IV) complex ions in glassy aqueous mixed hydrogen halide solutions were determined by Mössbauer and Raman spectroscopies. Trans-(SnF₄Cl₂)^2-, (SnCl₅Br)^2- and (SnCl₅Br)^2- and trans-(SnF₄Br₂)^2- ions are the main tin complex ions in the aqueous Sn(IV)-HF-HCl, Sn(IV)-HCl-HBr and Sn(IV)-HF-HBr solutions in the glassy state, respectively.     

Structure and photophysics of 2-(2'-pyridyl)benzindoles: the role of intermolecular hydrogen bonds

The photophysical properties of two isomeric 2-(2'-pyridyl)benzindoles depend on the environment. Strong fluorescence is detected in nonpolar and polar aprotic solvents. In the presence of alcohols, the emission reveals an unusual behavior. Upon titration of n-hexane solutions with ethanol, the fluorescence intensity goes through a minimum and then increases with rising alcohol concentration. Transient absorption and time-resolved emission studies combined with ground- and excited-state geometry optimizations lead to the conclusion that two rotameric forms, syn and anti, coexist in alcohols, whereas in nonpolar and aprotic polar media, only the syn conformation is present. The latter can form cyclic complexes with alcohols, which are rapidly depopulated in the excited state. In the presence of excess alcohol, syn --> anti rotamerization occurs in the ground state, promoted by the cooperative action of nonspecific and specific effects such as solvent polarity increase and the formation of hydrogen bonds to both donor and acceptor sites of the bifunctional compounds.     

Heteronuclear intermolecular resonance-assisted hydrogen bonds. The structure of pyrrole-2-carboxamide (PyCa)

The crystal and molecular structure of pyrrole-2-carboxamide (PyCa) determined by single crystal X-ray diffraction is presented. Molecular conformations of PyCa are also analyzed by FT-IR and NMR techniques. Additionally DFT calculations at the B3LYP/6-311++G(d,p) level of approximation are performed for dimers of PyCa and for related species. The existence of two tautomeric forms for the analyzed dimers differing in H-bond motifs, N-H...O or O-H...N, is studied. The geometrical and energetic features of such H-bonds show that these interactions may be classified as intermolecular resonance-assisted hydrogen bonds. Additionally the Bader theory is applied to determine and to analyze bond critical points.     

Computation of conformations of 2-(2-hydroxyethoxy)-3,4-dihydropyran with intramolecular hydrogen bonds

The conformations of 2-(2-hydroxyethoxy)-3,4-dihydropyran were calculated by the methods of molecular mechanics and MNDO/H with and without allowance for the formation of intramolecular hydrogen bonds. Two possible centers of the formation of the intramolecular hydrogen bond,viz., the oxygen atoms of the alkoxy radical and of the dihydropyran cycle, have been considered. The results obtained show that 2-(2-hydroxyethoxy)-3,4-dihydropyran does not exist in any preferable conformation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1202–1203, July, 1994.     

Competition between coordination bonds and hydrogen bonds: the nitrile-silver(I) interaction using dicyanobithiophene as ligand

Reactions of the ligand 5,5′-dicyano-2,2′-bithiophene (T₂CN₂) with a variety of silver(I) salts are presented. In most cases, the ligand precipitates by itself without incorporating the silver(I) metal. However, when the counterion is triflate, in benzene or THF, a coordination compound is formed. The crystal structure of the species grown from benzene, a double-stranded one-dimensional polymer, is reported. In this structure, the bithiophene ligand is twisted into the uncommon syn orientation. The reasons for the lack of reactivity of the ligand are discussed by comparing the relative strengths of the interligand hydrogen bond with the ligand–metal bond.     

Predicted signs of reduced two-bond spin-spin coupling constants (2hKX-Y) across X-H-Y hydrogen bonds

The reduced two-bond Fermi-contact terms and the reduced spin-spin coupling constants (2h)K(X-Y) across X-H-Y hydrogen bonds for complexes stabilized by C-H-N, N-H-N, O-H-N, F-H-N, C-H-O, O-H-O, F-H-O and C-H-F hydrogen bonds are positive. The NMR Triplet Wavefunction Model (NMRTWM) indicates that the signs of the reduced FC terms and (2h)K(X-Y) are determined by excited triplet states that have an odd number of nodes intersecting the X-Y axis between X and Y, thereby leading to an antiparallel alignment of the nuclear magnetic moments of atoms X and Y.     

Molecular structure and hydrogen bonds in solid dimethylol propionic acid (DMPA)

The H-bonds in dimethylol propionic acid (DMPA) are investigated through the spectra changes between -150 and 180 degrees C, the spectra comparison before and after the pendent carboxylic group was neutralized as well as after DMPA was partly deuterated. Vibrational bands assignment is proposed based on the group frequency, band shape, intensity and the crystal structure. It was found that the highly crystallized DMPA is also highly H-bonded with the obvious crystal relating bands besides the typical H-bonded characteristic bands of both alcohols and carboxylic acids. The packing mode of carboxylic acid is similar to long-chain polymers to some extent but possesses the dimer spectra characteristic, especially still showing the prominent out-of-plane bending vibrational band gammaOH. The three hydroxyls, including the carboxylic hydroxyl, are all in the different H-bond states, showing three H-bonded hydroxyl bands with different frequencies. The frequency, intensity and shape of nuOH relates not only to OH bond length, but also to H-bond length as well as the bond angle. The H-bond in carboxylic hydroxyl is more sensitive to temperature changes and deuteration whereas the two primary hydroxyls form another H-bond pattern after DMPA was neutralized. It was also found that the possible overtone of gammaOH appears at lower temperature.     

Photoinduced ion-pair formation in the (HI)m(H2O)n cluster system

The temporal behavior of the photoinduced ion-pair formation process in the (HI)m(H2O)n (n=1-6 for m=1 and n=1-4 for m=2) cluster system has been studied via the coupling between the g 3Sigma- Rydberg and V 1Sigma+ valence states. Comparison of the time constants obtained to those measured in previous experiments for the analogous process in HBr-water clusters, along with a detailed analysis of the signal intensity as a function of laser-pulse power, provides new insight into and confirmation of the previously proposed ion-pair formation mechanism.     

Intramolecular hydrogen bonds in the copper(II) complex withcis,cis-1,3,5-tri[2-(diphenylphosphoryl)ethylamino]cyclohexane

The formation of intramolecular hydrogen bonds in the complex ofcis,cis-1,3,5-tri[2-(diphenylphosphoryl)cthylamino]cyclohexanc with the Cu²⁺ cation in different solvents has been studied by IR spectroscopy. Conformational analysis of the complex has been performed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1537–1542, June, 1996.     

O-H ... O(S) hydrogen bonds in 2-hydroxy(thio)benzamides. Survey of spectroscopic and structural data

Summary From a survey of spectroscopic and structural data of six corresponding 2-hydroxybenzamides and 2-hydroxythiobenzamides (amide, N-methylamide, N,N-dimethylamide, piperidide, morpholide, 2,6-dimethylpiperidide) remarkable similarities between O(N)-H ... O and O(N)-H ... S hydrogen-bonds are obtained, concerning both, hydrogen-bond patterns and hydrogen-bond strengths. In dilute solution the OH groups of all compounds are intramolecularly associated to the (thio)carbonyl O (S) atoms with distinctly larger hydrogen-bond strengths for primary and secondary amides [ (O-H)=2950–3020 cm^–1, (OH)=12.16–11.99 ppm] and thioamides [ (O-H)=2960–3000 cm^–1, (OH)=11.65–11.13 ppm], than for tertiary amides [ (O-H)=3200–3250 cm^–1, (OH)=9.95–8.95 ppm] and thioamides [ (O-H)=3245–3330 cm^–1, (OH)=8.09–7.06 ppm]. In the solid state, the OH groups of the primary and secondary (thio)amides are also engaged in rather strong intramolecular O-H ... O=C [O ... O=2.51 Å, (O-H)=2700–2750 cm^–1] and O-H ... S=C [O ... S=2.90–2.94 Å, (O-H)=2700–2840 cm^–1] hydrogen-bonds; thetrans-NH groups of the primary (thio)amides and the NH groups of the secondary (thio)amides connect the molecules to N-H ... O-H [N ... O=2.93–3.10 Å, (N-H)=3319–3407 cm^–1] hydrogen-bonded chains; the remainingcis-NH groups of the primary (thio)amides give rise to eight-membered cyclic dimers via N-H ... O=C [N ... O=2.93 Å, (N-H)=3226 cm^–1] and N-H ... S=C [N ... S=3.46–3.47 Å, (N-H)=3233–3277 cm^–1] hydrogen-bonds. Contrary, the OH groups of the tertiary (thio)amides are intermolecular associated in the solid state and link the molecules to O-H ... O=C [O ... O=2.63–2.75 Å, (O-H)=3075–3135 cm^–1] and O-H ... S=C [O ... S=3.18–3.26 Å, (O-H)=3130–3190 cm^–1] hydrogen-bonded chains.

---

O-H ... O(S)-Wasserstoffbrückenbindungen in 2-Hydroxy(thio)benzamiden. Ein Überblick über spektroskopische und strukturelle Daten

Zusammenfassung Aus einer Zusammenstellung von spektroskopischen und strukturellen Daten von sechs entsprechenden 2-Hydroxybenzamiden und 2-Hydroxythiobenzamiden (Amid, N-Methylamid, N,N-Dimethylamid, Piperidid, Morpholid, 2,6-Dimethylpiperidid) ergeben sich bemerkenswerte Analogien zwischen O(N)-H ... O und O(N)-H ... S H-Brücken, die sowohl die H-Brücken-Muster als auch die H-Brücken-Stärken betreffen. In verdünnter Lösung sind die OH-Gruppen aller Verbindungen intramolekular mit den O(S)-Atomen der (Thio)Carbonylgruppen assoziiert, wobei die H-Brücken bei den primären und sekundären Amiden [ (O-H)=2950–3020 cm^–1, (OH)=12.16–11.99 ppm] und Thioamiden [ (O-H)=2960–3060 cm^–1, (OH)=11.65–11.13 ppm] deutlich stärker sind, als bei den tertiären Amiden [ (O-H)=3200–3250 cm^–1, (OH)=9.95–8.95 ppm] und Thioamiden [ (O-H)=3245–3330 cm^–1, (OH)=8.09–7.06 ppm]. Im Festkörper weisen die primären und sekundären (Thio)Amide ebenfalls sehr starke intramolekulare O-H ... O=C [O ... O=2.51 Å, (O-H)=2700–2750 cm^–1] und O-H ... S=C [O ... S=2.90–2.94 Å, (O-H)=2700–2840 cm^–1] H-Brücken auf; dietrans-NH-Gruppen der primären (Thio)Amide und die NH-Gruppen der sekundären (Thio)Amide verknüpfen die Moleküle über N-H ... O-H H-Brücken [N ... O=2.93–3.10 Å, (N-H)=3318–3407 cm^–1] zu Ketten; die verbleibendencis-NH-Gruppen der primären (Thio)Amide bilden zyklische, über N-H ... O=C [N ... O=2.93 Å, (N-H)=3226 cm^–1] und N-H ... S=C [N ... S=3.46–3.47 Å, (N-H)=3233–3277 cm^–1] H-Brücken gebundene, 8-Ring-Dimere. Im Gegensatz dazu sind die OH-Gruppen der tertiären (Thio)Amide im Festkörper intermolekular assoziiert und verknüpfen die Moleküle über O-H ... O=C [O ... O=2.63–2.75 Å, (O-H)=3075–3135 cm^–1] und O-H ... S=C [O ... S=3.18–3.26 Å, (O-H)=3130–3190 cm^–1] H-Brücken zu Ketten.

     

Oxidation of C-H bonds by [(bpy)2(py)RuIVO]2+ occurs by hydrogen atom abstraction

Anaerobic oxidations of 9,10-dihydroanthracene (DHA), xanthene, and fluorene by [(bpy)(2)(py)Ru(IV)O](2+) in acetonitrile solution give mixtures of products including oxygenated and non-oxygenated compounds. The products include those formed by organic radical dimerization, such as 9,9'-bixanthene, as well as by oxygen-atom transfer (e.g., xanthone). The kinetics of these reactions have been measured. The kinetic isotope effect for oxidation of DHA vs DHA-d(4) gives k(H)/k(D) > or = 35 +/- 1. The data indicate a mechanism of initial hydrogen-atom abstraction forming radicals that dimerize, disproportionate and are trapped by the oxidant. This mechanism also appears to apply to the oxidations of toluene, ethylbenzene, cumene, indene, and cyclohexene. The rate constants for H-atom abstraction from these substrates correlate well with the strength of the C-H bond that is cleaved. Rate constants for abstraction from DHA and toluene also correlate with those for oxygen radicals and other oxidants. The rate constant for H-atom transfer from toluene to [(bpy)(2)(py)Ru(IV)O](2+) appears to be close to that predicted by the Marcus cross relation, using a tentative rate constant for hydrogen atom self-exchange between [(bpy)(2)(py)Ru(III)OH](2+) and [(bpy)(2)(py)Ru(IV)O](2+).