Reply to comment on “H3O and OH, the real ions in aqueous acids and bases”

We have measured the quantum beats in the decay of pulse-excited “prompt” fluorescence in tetracene crystals as a function of magnetic field. We have demonstrated that counting the beats is a very simple and reliable method to study a possible influence of triplet-triplet interactions. In all so far performed experiments in tetracene crystals no influence has been found.     

Stability of equilibrium-top atoms

The stability of a new classical equilibrium configuration for two-electron atoms, a rotating rigid body atom, has been investigated. We identify this equilibrium configuration as hyperbolic fixed point in the phase space. The size of the classical atom turns out to be stable within a linear stability analysis, its quantum analog is therefore regarded as a new type of resonance. Binding is provided by motions along stable directions of the fixed point whereas unstable directions are responsible for a finite lifetime. The stable motions near the fixed point have no simple “molecular interpretation” in terms of periodic bending and stretching vibrations. Quasiperiodic unstable motions, however, are shown to exist.     

Localised vs delocalised molecular orbitals in aromatic hydrocarbons

In many series of polycyclic aromatic hydrocarbons, e.g. the acenes, phenes, starphenes, pyrenes, perylenes and coronenes, the first two IP's follow simple rules and can be predicted with sufficient accuracy from the IP's of the basic chromophores. For example, the PE spectra of all angularly annellated anthracenes show a persistent (“autonomous”) band at 7.4 eV; in the tetracenes such a band is found at 7.0 eV, in the pentacenes at 6.6 eV. The PE spectrum of hexaphene is essentially a superposition of the spectra of tetracene and anthracene, and the spectrum of heptaphene resembles that of tetracene, with all bands showing twice the normal integrated intensity. The bands in the spectra of the linearly annellated pyrenes can be classified into pyrene and acene-type bands of which only the latter respond to annellation (“moving” bands). Similar observations can be made in angularly annellated perylenes and the linearly annellated coronenes. Isotopic hydrocarbons, i.e. compounds with identical UV band positions, show surprising similarities in their PE spectra, despite the widely differing topologies. The origin of these regularities is discussed in terms of the sextet formalism and Hückel theory. Applications to structure elucidation are pointed out.     

General methods of analysing molecular vibrations

An acute need may arise to develop for the complete analysis of molecular vibrations practically convenient general methods based on coordinates other than “chemical coordinates”. One reason is the proven proposition: Among independent internal coordinates corresponding to a molecule, there cannot be one which describes a small displacement of a chemical group as a whole relative to a certain molecular plane, provided this group contains more than two linearly or three non-linearly arranged atoms. Two methods are presented in some detail. The first is based on the use of X⁰_δ coordinates which are components of “bond vectors” in the “sown” (for each “bond”) Cartesian coordinate system. The second method utilizes X⁰ coordinates, i.e. the components of atomic displacements in the “down” (for each atom) Cartesian coordinate system. Computation of the torsional vibration of transdichloroethane is given as an example illustrating the first method. The Mayants treatment of the symmetry of a molecule, proceeding from elementary considerations which do not use the group theory explicitly and are valid for any coordinates, is expounded in a somewhat improved version. The peculiarities arising when considering the mean-square amplitude matrix, Σ, in X⁰_δ and X⁰ coordinates are also discussed.     

Vibronic coupling in the ground and excited states of oligoacene cations

The vibrational coupling in the ground and excited states of positively charged naphthalene, anthracene, tetracene, and pentacene molecules is studied on the basis of a joint experimental and theoretical study of ionization spectra using high-resolution gas-phase photoelectron spectroscopy and first-principles correlated quantum-mechanical calculations. Our theoretical and experimental results reveal that, while the main contribution to relaxation energy in the ground state of oligoacene systems comes from high-energy vibrations, the excited-state relaxation energies show a significant redistribution toward lower-frequency vibrations. A direct correlation is found between the nature of the vibronic interaction and the pattern of the electronic state structure.     

Toward a Consistent Interpretation of the QTAIM: Tortuous Link between Chemical Bonds,Interactions, and Bond/Line Paths

Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, “misinterpretations” of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM’s topological analysis of the one‐electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the “interaction” to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed “line paths” in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some “problematic” molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new “interpretation” of data is performed.     

Studies of chemisorbed tetracene on si(111)-7x7

The chemisorption of tetracene on the Si(111)-7x7 surface was studied using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. On the basis of the STM results and dimension analysis, two types of binding configurations were proposed. One of the configurations involves the di-sigma reaction between two C atoms of an inner ring with an adatom-rest atom pair on the substrate to give rise to an unsymmetrical butterfly structure. Tetracene in another configuration possesses four C-Si bonds that are formed via di-sigma reactions between the C atoms at the terminal rings with two center adatom-rest atom pairs within one-half of the surface unit cell. Besides, two other binding modes were proposed based on the dimension compatibility between the tetracene C and the substrate Si dangling bonds even though their identifications through the STM images are nonexclusive. Structural modeling and adsorption energies calculations were carried out using the DFT method. Factors affecting the relative thermodynamic stabilities based on the calculation results and the relative populations of tetracene in the different binding configurations as observed experimentally were discussed.     

Pyrene‐fused Acenes and Azaacenes: Synthesis and Applications

In this account, the synthesis and applications of pyrene‐fused acenes, as well as pyrene‐fused azaacenes, have been carefully reviewed. Moreover, the synthetic methods involving two key synthons (different lengths of dienes and ynes) have been included. Furthermore, the “clean reaction” strategy has been introduced for the preparation of pyrene‐fused acenes with a single terminal‐pyrene unit from tetracene to octacene, as well as for the synthesis of pyrene‐fused octatwistacenes and nonatwistacenes with double terminal‐pyrene units. Similarly, the synthons and the synthetic methods for pyrene‐fused azaacenes have also been summarized. The applications of pyrene‐fused acenes and pyrene‐fused azaacenes have been included.     

Chemistry of exciplexes 11: Photocycloaddition of 1,3-cyclohexadiene to polynuclear aromatic hydrocarbons

Extending our investigations on the photochemical reactions between benzenoid aromatic hydrocarbons and conjugated polyunsaturated olefins to the higher arenes, we describe the pericyclic reactivity evidenced in the photochemical cycloaddition reactions of anthracene, tetracene, benz(a)anthracene, dibenz(a,c)anthracene, dibenz(a,h)anthracene, dibenz(a,j)anthracene and pentaphene with 1,3-cyclohexadiene. The divergent reactivities of these arenes is not explicable in terms of Woodward-Hoffmann or derivative theories. We attribute the proclivities of these systems to engage in pericyclic cycloaddition reactions, and in particular the failure of dibenz(a,h)anthracene and pentaphene to from “allowed” 4π_s + 4π_s meso cycloadducts, to a requirement for the preservation of “essential symmetry” about the reactive positions, wherein the local nodal structure of the reactants must correlate with that of the products for a pericyclic process to be energetically competitive with other modes of deactivation of the arene excited state. Applicability of this theory in thermal processes is also considered.     

A V‐Shaped Polyaromatic Amphiphile: Solubilization of Various Nanocarbons in Water and Enhanced Photostability

Nanocarbons are synthetic carbon‐rich compounds with polyaromatic frameworks that have lately attracted attention as emerging functional materials. However, their extreme hydrophobicity and aggregation peculiarity, besides their shape and size diversities, precluded their study in solution, especially in “green” water. More convenient and general solubilizing methods of nanocarbon frameworks are required by using non‐covalent supramolecular interactions. Here we report a protocol for solubilizing a wide range of nanocarbons, that is, fullerenes (C₆₀, C₇₀, C₈₄, and C₁₂₀), polyarenes (tetracene, pentacene, perylene, coronene, and hexabenzocoronene), and carbon nanotubes (single‐walled and multi‐walled CNTs), in water through manual grinding with V‐shaped polyaromatic amphiphiles. The obtained aqueous nanocomposites are composed of nanocarbons encircled by the polyaromatic frameworks of the amphiphiles through multiple aromatic–aromatic interactions. Notably, the encapsulated photosensitive nanocarbons, such as tetracene, pentacene, and fullerene dimer, exhibit unusual stability toward UV/Vis light.     

Surface of liquid helium as a trap for rydberg atom. Mechanisms of relaxation

Recently, the special interest to the exploration of the system “atom adsorbed on the cryogenic surface” has emerged. This interest is concerned with the construction of the hydrogen masers [1], which are important for metrological applications, with the preparation of the high densities of the quantum states of the spin-polarized hydrogen type [2] and with studies of transfer processes in highly degenerate systems [3]. In the paper [4] the authors considered the adsorption of the Rydberg atom by the cryogenic surfaces of the dielectric (see, also [19]). The bound state of an atom with a surface is formed, consisting of a ionic core and a highly excited electron. The wave functions of electron can be “semi-spheric” (the interaction with ionic core exceeds the interaction of the electron with its image) or “flat” depending on the level of excitation of an atom.     

A study on the transition state in the photooxygenations by aromatic amine N-oxides

Oxygen—atom transfer process in the photolysis of aromatic amine N-oxides was suggested to involve the primary oxygen—atom elimination from N-oxides to give “oxene” follwed by its reactions with the oxygen-acceptors.     

Alternative mechanisms of electrophilic substitution in azole series

Data on three mechanisms of aromatic electrophilic substitution in azole series have been presented. First of them is similar to an ordinary addition–elimination mechanism including the formation of a cationic σ-complex (Wheland intermediate). The second mechanism is realized according to the elimination–addition scheme and includes a protonation or a formation of a complex on the “pyridine” N atom, proton abstraction from the C atom adjacent to the above N atom, and addition of a cationoid reagent to the ylide (carbene) formed. The third mechanism proposed by the present authors can be realized for azoles having three and two N atoms of the pyridine type. It does not require the preliminary N-protonation or complex formation and occurs due to a strong electron withdrawing effect of several “pyridine” atoms, resulting in the CH-deprotonation followed by the interaction of the carbanion formed with a cation under mild conditions.     

Application of the dimer approach for the analysis of vibrational spectra of BEDT—TTF-based charge-transfer salts

The dimer approach was proposed for the normal coordinate analysis of BEDT—TTF⁺ molecular vibrations. It was shown that, within the framework of the approximation used, the appearance of additional bands in the IR as well as in Raman spectra may be explained as due to the reduction of symmetry of the dimerized system in comparison with the monomeric one. The strength of intermolecular interaction in the dimer was estimated by adjusting the calculated frequencies to the observed positions of intense “vibronic” bands recorded in the IR spectra of BEDT—TTF-based monovalent charge transfer salts. It was found that for the reproduction of “vibronic shifts” observed for some vibrations it should be assumed that the intermolecular interaction takes effect not only on the totally symmetric a_g modes, but also on the vibrations of other symmetry species.     

A general approach for atom-type assignment and the interconversion of molecular structure files

In molecular modeling projects which require use of several different computer programs, one encounters problems in sharing data between programs. One difficult problem is the conversion of atom types from one program's definition to another. A second problem is the conversion of a polymer, such as a protein or polynucleotide molecule, from a “general” program, which understands molecules as a collection of atoms, to a “polymer” program, which understands molecules as a collection of molecular fragments stored in some library. We describe here a new method by which atom types are deduced from the environment of each atom. We use the Daylight Chemical Information Systems library of programs to deduce the atom types based only on the atomic symbol, connectivity and formal charge of each atom in the molecule. We also describe a method by which the polypeptide nature and sequence of a molecule can be deduced from minimal information about the atoms in the molecule. We have written a computer program which demonstrates this method. This program deduces atom types for AMBER, GRIN/GRID, CHARMm, and ALOGP. It will also produce input files for the AMBER/PREP fragment library preparation program.     

高中化学新教材中VSEPR模型的b值规定之刍议

新教材关于VSEPR模型中b值的计算,暂未考虑"与中心原子结合的原子"所处的位置环境,即只做了静态规定,是符合新课标要求的;但若拓展运用在CH3COOH这样常见的分子上,会出现与常识不相符的情况,使得VSEPR模型的适用范围受限.从拓展高中化学的教与学的角度出发,笔者认为,将"与中心原子结合的原子"所处的位置环境考虑在...     

Interionic vibrations and the molecular structure of ion pairs for 1-acetylpyridinium halides

The structure and interionic vibrations of the ion pairs of 1-acetylpyridinium halides have been analysed by the joint use of far-IR spectroscopy, a molecular orbital method and molecular mechanics calculations. It has been found that these ion pairs are non-rigid molecules with large amplitude low-frequency interionic vibrations. The most probable ion pair geometry corresponds to the anion location over the plane of the cation pyridinium ring. The nature of chemical bonding between the anion and cation has been established to be predominantly ionic.     

A new possibility for determining vibration frequencies of organic molecules in the excited electronic state from fluorescence spectra

The dependence of the fluorescence spectra of some aromatic hydrocarbons and phthalocyanines in solid solutions at 4.2 K on the frequency of laser excitation has been studied. It has been found that “multiplets” exist in the fluorescence spectra in the case when laser excitation occurs in the vibronic transition region. The structure of these “multiplets” does not depend on the solvent but changes considerably with a change of laser frequency. It has been shown that by analysing the above-mentioned “multiplets” one can obtain frequencies of vibrations of the investigated molecules in excited electronic states.     

The destabilization of hydrogen bonds in an external E-field for improved switch performance

The effect of an electric field on a recently proposed molecular switch based on a quinone analogue was investigated using next-generation quantum theory of atoms in molecules (QTAIM) methodology. The reversal of a homogenous external electric field was demonstrated to improve the “OFF” functioning of the switch. This was achieved by destabilization of the H atom participating in the tautomerization process along the hydrogen bond that defines the switch. The “ON” functioning of the switch, from the position of the tautomerization barrier, is also improved by the reversal of the homogenous external electric field: this result was previously inaccessible. The “ON” and “OFF” functioning of the switch was visualized in terms of the response of the most preferred directions of motion of the electronic charge density to the applied external field. All measures from QTAIM and the stress tensor provide consistent results for the factors affecting the “ON” and “OFF” switch performance. Our analysis therefore demonstrates use for future design of molecular electronic devices. © 2019 Wiley Periodicals, Inc.     

Chemistry of the Positron and of Positronium

In this progress report, the properties and behavior of the positron (“positive electron”, anti-electron) and of the positronium, a “hydrogen atom” containing a positron instead of a proton, are considered from the chemist's viewpoint. Examples are given to demonstrate the development of positronium chemistry, in aqueous solution and in the gaseous, liquid, and solid phases, with its problems and possibilities.