Stoichiometry and mechanism of protonation of alkali metal salts of benzophenone radical anions by weak proton donors and its relevance to the base-catalyzed decomposition of benzopinacol

The Stoichiometry of the protonation of lithium and potassium salts of benzophenone radical anions and of the lithium salt of the fluorenone radical anion by methanol has been measured and found to be [(Ar₂C=O)^–]/[MeOH] =21. This result, which was obtained by the method of magnetic titration, implies that paramagnetism decays by the reaction between a ketyl anion and a ketyl radical (i.e., a protonated ketyl anion). The reactivities of alkali metal salts of fluorenone radical anions in relation to methanol exhibit a pronounced dependence on the nature of the counterion. No kinetic deuterium isotope effect has been found for the protonation of the lithium salt of the benzophenone radical anion in tetrahydrofuran (THF) bytert-pentyl alcohol. The lithium salt of the benzophenone radical anion inN,N,N,N-tetramethylethylenediamine (TMEDA) behaves markedly differently. Namely, its protonation by methanol exhibits 1 1 Stoichiometry and it reacts considerably more slowly withsec-butyl alkohol,K(THF)/K(TMEDA) = 2.5. Benzopinacol undergoes decomposition by an alkoxide base to diphenyl ketyl, which decays into an equimolar mixture of benzophenone and benzhydrol. The reaction follows second-order kinetics and the specific rate constants exhibit an inverse relationship with respect to the initial concentration of the alkoxide. With a very strong base benzopinacol decomposes into two diphenyl ketyl anions. On the basis of this information as well as on studies of products, relevant mechanisms are proposed for the protonation of ketyl anions and for the decomposition of aromatic pinacols in basic media.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 83–91, January, 1995.     

Synthesis and Protonation Features of 24-, 27- and 32-membered Macrocyclic Polyamines

Three macrocyclic polyamines [24]ane-N₆ 1 , [32]ane-N₈ 2 and [27]ane-N₆O₃ 3 of ring size 24, 32 and 27, respectively, have been synthesized. They contain either trimethylenediamine of ethylenediamine units. The acyclic analog 4 , as the reference compound, was also prepared. Compounds 1–3 are macrocyclic analogs of natural polyamines and are potential ligands for metal cations as well as, when protonated, for anions. The protonation constants of compounds 1–4 have been determined. They are high enough for compounds 1–4 to be fully protonated in a pH-range close to neutrality, as required for binding of anions of weak acids. The effect of structural features on the protonation constants are briefly discussed in relation to the design of macrocyclic polyamine ligands.     

A theoretical study on the protonation of cycloalkanes CnH2n (n = 3 to 6)

Ab initio self-consistent-field molecular orbital calculations have been carried out for the C_nH_2n (n = 3 to 6) cycloalkanes and various conformers of their protonated forms. The calculated protonation energies for the sequence of conformers of the protonated forms follow the experimentally observed trend. Correlations between optimum C? C? C bond angles at the protonation site and the calculated protonation energies have been observed, and these correlations may be of some use in estimating protonation energy-bond angle relations in other (strained) cyclic compounds when the central carbon atom of a C? C? C moiety is protonated.     

The gas-phase reaction of hydrazine and ozone: A nonphotolytic source of OH radicals for measurement of relative OH radical rate constants

The homogeneous gas-phase reaction of N₂H₄ with O₃ in air atmospheric pressure has been used to generate OH radicals in the dark, allowing the determination of relative OH radical rate constants for compounds which photolyze rapidly. This technique was first validated by determining the OH radical rate constant ratios for n-butane/cyclohexane and methanol/dimethyl ether, both of which are in excellent agreement with the literature values. The rate constant for the reaction of OH radicals with methyl nitrite at 300 ± 3 K was then determined relative to those for the reaction of OH radicals with n-hexane and dimethyl ether. The resulting rate constant of 1.8 × 10^?13 cm³/molecule·s is about seven times lower than those of previous measurements which employed a different nonphotolytic relative rate method.     

Synthesis,crystal structures and anticancer activities of two decavanadate compounds

Two ammonium decavanadate(V) compounds, (H₂tmen)₃V₁₀O₂₈·6H₂O (1) and (H₂en)₃V₁₀O₂₈·2H₂O (2), where H₂tmen and H₂en represent the doubly protonated N,N,N′,N′-tetramethylethylenediammonium ion and doubly protonated ethylenediammonium ion, respectively, have been synthesized and structurally characterized by elemental analyses, spectroscopic (i.r., e.s.r.) studies, and single-crystal X-ray diffraction. Both crystal structures reveal the presence of the [V₁₀O₂₈]⁶⁻ cluster anions, doubly protonated diammonium cations, and lattice water molecules. Hydrogen bonds assemble these two compounds to form three-dimensional networks. The in vitro anticancer activity against A549 and P388 tumor cells lines has also been determined by the MTT-based assay, and the results suggest that both compounds can inhibit proliferation of these two kinds of tumor cells.     

Tunable Electronic Properties of a Proton‐Responsive N,N‐Dimethylaminoazobenzene Fullerene (C60) Dyad

A basic N,N‐dimethylaminoazobenzene–fullerene (C₆₀) dyad molecular skeleton is modelled and synthesized. In spite of the myriad use of azobenzene as a photo‐ and electrochromic moiety, the idea presented herein is to adopt a conceptually different path by using it as a bridge in a donor–bridge–acceptor single‐molecular skeleton, connecting the electron acceptor N‐methylfulleropyrrolidine with an electron donor N,N‐dimethylaniline. Addition of trifluoroacetic acid (TFA) results in a drastic colour change of the dyad from yellow to pink in dichloromethane (DCM). The structure of the protonated species are established from electronic spectroscopy and time‐dependent density functional theory (TD‐DFT) calculations. UV/Vis spectroscopic investigations reveal the disappearance of the 409 nm ¹(π→π*) transition with appearance of new features at 520 and 540 nm, attributed to protonated β and α nitrogens, respectively, along with a finite weight of the C₆₀ pyrrolidinic nitrogen. Calculations reveal intermixing of n_(N?N)→π*_(N?N) and charge transfer (CT) transitions in the neutral dyad, whereas, the n_(N?N)→π*_(N?N) transition in the protonated dyad is buried under the dominant ¹(π →π*) feature and is red‐shifted upon Gaussian deconvolution. The experimental binding constants involved in the protonation of N,N‐dimethylanilineazobenzene and the dyad imply an almost equal probability of existence of both α‐ and β‐protonated forms. Larger binding constants for the protonated dyads imply more stable dyad complexes than for the donor counterparts. One of the most significant findings upon protonation resulted in frontier molecular orbital (FMO) switching with the dyad LUMO located on the donor part, evidenced from electrochemical investigations. The appearance of a new peak, prior to the first reduction potential of N‐methylfulleropyrrolidine, clearly indicates location of the first incoming electron on the donor‐centred LUMO of the dyad, corroborated by unrestricted DFT calculations performed on the monoanions of the protonated dyad. The protonation of the basic azo nitrogens thus enables a rational control over the energetics and location of the FMOs, indispensable for electron transport across molecular junctions in realizing futuristic current switching devices.     

ESR Spectra of radicals produced by reduction of pyridine and pyrazine

Radicals produced by reaction of e^?_aq with pyridine, pyrazine, and pyrazinedicarboxylic acid have been studied by electron spin resonance using the in situ radiolysis steady-state ESR technique. The radical anions initially produced have been found to undergo rapid protonation on nitrogen to form pyridinyl and pyrazinyl radicals. The NH proton of pyridinyl radical does not dissociate even at pH 13.7. The radical from pyrazine has been observed only in the doubly protonated positively charged form in acid and neutral solutions, but no spectrum was observed in alkaline media. With 2,3-pyrazinedicarboxylic acid the doubly protonated radical has been observed at pH 4–8 and the singly protonated one at pH 11–12. The pK for this dissociation is 9.2. The hyperfine constants of the pyridinyl radical are compared with those obtained from INDO molecular orbital calculations.     

N-Hydroxyurea dimers: A matrix isolation and theoretical study

The dimerization of N-hydroxyurea (NH₂CONHOH) has been investigated by FTIR matrix isolation spectroscopy and DFT(B3LYP)/6-311++G(2d,2p) calculations. The analysis of NH₂CONHOH/Ar matrix spectra and comparison with theoretical ones reveal the formation of two types of dimers with a strong OH⋯O hydrogen bond. There is an additional weak interaction between the oxygen atom of the OH group of the proton donor molecule and the NH or NH₂ group of the proton acceptor in both dimers, respectively. The identified structures correspond to local minima on the PES. The formation of the less stable structures not the most stable ones indicates that the creation of N-hydroxyurea dimers is related to the dipole-dipole interaction at the initial stage of the dimerization process, which favours generation of polar dimers.     

Nitroarene products from the gas-phase reactions of volatile polycyclic aromatic hydrocarbons with the OH radical and N2O5

The nitroarene products of the gas-phase reactions of acenaphthylene, acenaphthene, phenanthrene, and anthracene-d₁₀ with N₂O₅ and the OH radical (in the presence of NO_x) are reported. The calculated atmospheric lifetimes of these polycyclic aromatic hydrocarbons (PAH), as well as those of naphthalene, 1- and 2-methylnaphthalene, biphenyl, fluoranthene, pyrene, and acephenanthrylene, show that reaction with the OH radical is the dominant loss process for these PAH, with the exception of acenaphthylene, acenaphthene, and acephenanthrylene which contain an external cyclopenta-fused ring. For these latter PAH, reaction with the NO₃ radical, and for acenaphthylene and acephenanthrylene reaction with O₃, are also expected to be important atmospheric loss processes. The nitroarenes observed as products of the atmospherically-important gas-phase reactions of the PAH in environmental chamber studies are compared with the nitroarenes measured in ambient air samples collected in California. It is concluded that although nitroarenes are formed in low yields (?5%) from the OH radical-initiated reactions of the PAH, atmospheric formation of nitroarenes may contribute significantly to ambient nitroarene concentrations.     

Resonance Raman spectroscopy and DFT calculations of the protonation of 4-(2-pyridylazo)-N,N-dimethylaniline in solution and adsorbed on oxide surfaces

The protonation of 4-(2-pyridylazo)-N,N-dimethylaniline (PYAD) in aqueous solution and its adsorption on oxide surfaces has been studied by resonance Raman (RR) spectroscopy. The gas phase structures of neutral, protonated and diprotonated forms of PYAD were modelled by SCF-DFT calculations at the B3-LYP/DZ level, enabling determination of the simulated vibrational spectra of these species, together with vibrational assignments, and providing confirmation that protonation occurs initially at the pyridyl nitrogen atom. Electronic absorption spectra were interpreted using time-dependent DFT calculations. Adsorption of PYAD on SiO₂ or Al₂O₃ surfaces is mainly via the neutral species, hydrogen bonded to surface OH groups, although a small proportion of adsorbed molecules are protonated. By contrast, adsorption on SiO₂–Al₂O₃ results in complete protonation, indicating the presence of Brønsted acidic sites with pK_a values ? 4.5, whereas adsorption on H-mordenite results in diprotonation, indicating the presence of Brønsted acidic sites with pK_a values ? 2.     

Gas phase sulfur anions: Synthesis and reactions of H2NS− and related ions

Many gas-phase anions react with carbonyl sulfide by sulfur atom transfer to form RS^? ions. The properties of H₂NS^?, formed in this way from H₂N^? and OCS, are described.     

Molecular surface electrostatic potentials and local ionization energies of Group V–VII hydrides and their anions: Relationships for aqueous and gas-phase acidities

We have computed ab initio HF /6-31+G * electrostatic potentials and average local ionization energies on the molecular surfaces of the Group V–VII hydrides and corresponding anions of the first three rows of the periodic table. The surfaces were defined to be specified contours (0.002 or 0.001 au) of the molecular electronic density. The most negative potentials, V_S,min, and lowest ionization energies ī_S,min, were located and determined. Their magnitudes separately satisfy limited correlations with gas-phase protonation enthalpies and aqueous pK_a values. Our results indicate that V_S,min, and ī_S,min are complementary, the former reflecting electrostatic factors and the latter being related to charge transfer/polarization. More general relationships for protonation enthalpies are obtained when both V_S,min and ī_S,min are explicitly included. Solution-phase and gas-phase acidities are shown to correlate very well if electrostatic effects are explicitly taken into account. © 1993 John Wiley & Sons, Inc.     

Influence of protonation on the geometry of 2-{[(2,6-dimethylphenoxy)ethyl]amino}-1-phenylethan-1-ol: crystal structures of the free base and of its chloride and 3-hydroxybenzoate salt forms

The aroxyalkylaminoalcohol derivatives are a group of compounds known for their pharmacological action. The crystal structures of four new xylenoxyaminoalcohol derivatives having anticonvulsant activity are reported, namely, 2-{[2-(2,6-dimethylphenoxy)ethyl]amino}-1-phenylethan-1-ol, C₁₈H₂₃NO₂, 1 , the salt N-[2-(2,6-dimethylphenoxy)ethyl]-1-hydroxy-1-phenylethan-2-aminium 3-hydroxybenzoate, C₁₈H₂₄NO₂⁺·C₇H₅O₃^?, 2 , and two polymorphs of the salt (R)-N-[2-(2,6-dimethylphenoxy)ethyl]-1-hydroxy-1-phenylethan-2-aminium chloride, C₁₈H₂₄NO₂⁺·Cl^?, 3 and 3p . Both polymorphs crystallize in the space group P2₁2₁2 and each has two cations and two anions in the asymmetric unit (Z′ = 2). The molecules in the polymorphs show differences in their molecular conformations and intermolecular interactions. The crystal packing of neutral 1 is dominated by intermolecular O—H…N hydrogen bonds, resulting in the formation of one-dimensional chains. In the crystal structures of the salt forms ( 2 , 3 and 3p ), each protonated N atom is engaged in a charge-assisted hydrogen bond with the corresponding anion. The protonation of the N atom also influences the conformation of the molecular linker between the two aromatic rings and changes the orientation of the rings. The crystal packing of the salt forms is dominated by intermolecular O—H…O hydrogen bonds, resulting in the creation of chains and rings. Structural studies have been enriched by the calculation of Hirshfeld surfaces and the corresponding fingerprint plots.     

Gas-phase fragmentation of long-lived cysteine radical cations formed via no loss from protonated S-nitrosocysteine

In this work, we describe two different methods for generating protonated S-nitrosocysteine in the gas phase. The first method involves a gas-phase reaction of protonated cysteine with t-butylnitrite, while the second method uses a solution-based transnitrosylation reaction of cysteine with S-nitrosoglutathione followed by transfer of the resulting S-nitrosocysteine into the gas phase by electrospray ionization mass spectrometry (ESI-MS). Independent of the way it was formed, protonated S-nitrosocysteine readily fragments via bond homolysis to form a long-lived radical cation of cysteine (Cys^•+), which fragments under collision-induced dissociation (CID) conditions via losses in the following relative abundance order: •COOH ≫ CH₂S > •CH₂SH-H₂S. Deuterium labeling experiments were performed to study the mechanisms leading to these pathways. DFT calculations were also used to probe aspects of the fragmentation of protonated S-nitrosocysteine and the radical cation of cysteine. NO loss is found to be the lowest energy channel for the former ion, while the initially formed distonic Cys^•+ with a sulfur radical site undergoes proton and/or H atom transfer reactions that precede the losses of CH₂S, •COOH, •CH₂SH, and H₂S.     

Hydro­gen‐bonding patterns in 2‐amino‐4,6‐di­methyl­pyrimidinium hydrogen sulfate

In the title compound, C₆H₁₀N₃⁺·HSO₄⁻, the asymmetric unit consists of a hydrogen sulfate anion and a 2‐amino‐4,6‐di­methyl­pyrimidinium cation. The hydrogen sulfate anions self‐assemble through O—H⋯O hydrogen bonds, forming supramolecular chains along the b axis, while the organic cations form base pairs via N—H⋯N hydrogen bonds. The amino­pyrimidinium cations join to the sulfate anions via a pair of hydrogen bonds donated from the pyrimidinium protonation site and from the exo amine group cis to the protonated site.     

ESR.-Messungen an Radikal-Anionen Trimethylsilyl-substituierter Hetero-π-Systeme

The ESR. spectra of the radical anions of trimethylsilyl-substituted derivatives of p-benzoquinone, phenylketone, diimine, p-benzoquinone-diimide, aniline and p-phenylenediamine are reported. In most cases the coupling constants of ²⁹Si isotopes in natural abundance have been measured. The comparison of the ESR. data for the radical anions of the trimethylsilyl derivatives with those for the radical anions of the corresponding parent hydrocarbons and/or alkyl-substituted compounds provide additional evidence for the overall electron withdrawing effect of the trimethylsilyl substituent (Si←C_π and Si←n_π delocalization).     

Hydride transfer reactions via ion–neutral complex: fragmentation of protonated N‐benzylpiperidines and protonated N‐benzylpiperazines in mass spectrometry

An ion‐neutral complex (INC)‐mediated hydride transfer reaction was observed in the fragmentation of protonated N‐benzylpiperidines and protonated N‐benzylpiperazines in electrospray ionization mass spectrometry. Upon protonation at the nitrogen atom, these compounds initially dissociated to an INC consisting of [RC₆H₄CH₂]⁺ (R = substituent) and piperidine or piperazine. Although this INC was unstable, it did exist and was supported by both experiments and density functional theory (DFT) calculations. In the subsequent fragmentation, hydride transfer from the neutral partner to the cation species competed with the direct separation. The distribution of the two corresponding product ions was found to depend on the stabilization energy of this INC, and it was also approved by the study of substituent effects. For monosubstituted N‐benzylpiperidines, strong electron‐donating substituents favored the formation of [RC₆H₄CH₂]⁺, whereas strong electron‐withdrawing substituents favored the competing hydride transfer reaction leading to a loss of toluene. The logarithmic values of the abundance ratios of the two ions were well correlated with the nature of the substituents, or rather, the stabilization energy of this INC. Copyright © 2010 John Wiley & Sons, Ltd.     

N‐{3‐[(2‐Ammonioethyl)amino]propyl}ethane‐1,2‐diaminium tris(trifluoromethanesulfonate): a salt of a folded triply protonated tetramine

The structure of a trifluoromethanesulfonate salt of a nontypical triply protonated linear tetramine, C₇H₂₃N₄³⁺·3CF₃SO₃⁻, with a layered crystal structure is presented. One N atom remains unprotonated. The conformation of the cation is enforced by intra‐ and intermolecular hydrogen bonds. The crystal structure is built of ca 10 Å deep layers, within which cations and anions are hydrogen bonded. Each layer is only weakly bound to its neighbours. This study shows a rare example of an unsymmetrically protonated polyamine and the relation between the lack of protonation, intramolecular hydrogen bonding and the conformation of the cation.     

Rate constants for the gas-phase reactions of cis-3-Hexen-1-ol,cis-3-Hexenylacetate,trans-2-Hexenal,and Linalool with OH and NO3 radicals and O3 at 296 ± 2 K,and OH radical formation yields from the O3 reactions

Rate constants for the gas-phase reactions of the four oxygenated biogenic organic compounds cis-3-hexen-1-ol, cis-3-hexenylacetate, trans-2-hexenal, and linalool with OH radicals, NO₃ radicals, and O₃ have been determined at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm³ molecule^?1 s^?1 units): cis-3-hexen-1-ol: (1.08 ± 0.22) × 10^?10 for reaction with the OH radical; (2.72 ± 0.83) × 10^?13 for reaction with the NO₃ radical; and (6.4 ± 1.7) × 10^?17 for reaction with O₃; cis-3-hexenylacetate: (7.84 ± 1.64) × 10^?11 for reaction with the OH radical; (2.46 ± 0.75) × 10^?13 for reaction with the NO₃ radical; and (5.4 ± 1.4) × 10^?17 for reaction with O₃; trans-2-hexenal: (4.41 ± 0.94) × 10^?11 for reaction with the OH radical; (1.21 ± 0.44) × 10^?14 for reaction with the NO₃ radical; and (2.0 ± 1.0) × 10^?18 for reaction with O₃; and linalool: (1.59 ± 0.40) × 10^?10 for reaction with the OH radical; (1.12 ± 0.40) × 10^?11 for reaction with the NO₃ radical; and (4.3 ± 1.6) × 10^?16 for reaction with O₃. Combining these rate constants with estimated ambient tropospheric concentrations of OH radicals, NO₃ radicals, and O₃ results in calculated tropospheric lifetimes of these oxygenated organic compounds of a few hours. © 1995 John Wiley & Sons, Inc.     

Physicochemical Properties of Polyaniline Base and Salt Films

Abstract

Polyaniline base and perchlorate salt films cast from N-methylpyr-rolidinone (NMP) solutions are studied using thermogravimetric analysis, infrared and ultraviolet-visible absorption spectroscopy, and x-ray photoelectron spectroscopy. Both types of films retain a substantial amount of solvent. Although most of the solvent can be removed by washing the films with deionized water, some C1O^? ₄ anions are removed from the salt films as well, resulting in a decrease in conductivity. In the salt films, protonation of the amine units in addition to the imine units can be readily achieved using HC1O₄. Structural modifications of the base films are apparent after one reprotonation/deprotonation cycle. These result in a decrease in the solubility of the film, the extent of which increases with the protonation level. Although NMP is a useful solvent for casting polyaniline salt and base films, both leucoemeraldine and perchloric acid protonated salt undergo degradation in this solvent.