Interaction between ions and substituted buckybowls: A comprehensive computational study

Complexes formed by substituted buckybowls derived from corannulene and sumanene with sodium cation or chloride anion have been computationally studied by using a variety of methods. Best results have been obtained with the SCS‐MP2 method extrapolated to basis set limit, which reproduces the highest‐level values obtained with the MP2.X method. All bowls form stable complexes with chloride anion, with stabilities ranging from ?6 kcal/mol in the methylated corannulene derivative to ?45 kcal/mol in the CN‐substituted sumanene. The opposite trend is observed in sodium complexes, going from deeply attractive complexes with the methylated derivatives (?36 kcal/mol with sumanene derivative) to slightly repulsive ones in the CN‐substituted bowls (2 kcal/mol in the corannulene derivative). Anion complexes are stabilized by large electrostatic interactions combined with smaller though significant dispersion and induction contributions. Conversely, cation complexes are stabilized by large induction contributions capable of holding together the bowl and the cation even in cases where the electrostatic interaction is repulsive. The effect of substitution is mainly reflected on changes in the molecular electrostatic potential of the bowl and, thus, in the electrostatic contribution to the interaction. Therefore, the variations in the stability of the complexes on substitution could be roughly predicted just considering the changes in the electrostatic interaction. However, other contributions also register changes mainly as a consequence of displacements on the position of the ion at the minimum, so the accurate prediction of the stability of this kind of complexes requires going further than the electrostatic approach. © 2014 Wiley Periodicals, Inc.     

Photodetachment of electrons from tetracyanoethylene negative ions

A crossed beam experiment using a surface ionization negative ion source and a xenon are lamp has allowed the relative cross section for photodetachment of an electron from a negative ion of tetracyanoethylene to be determined for photons in the energy range 2.1—3.5 eV (590—350nm). The threshold energy was found to be 2.03 ± 0.07 eV.     

NH4I/EtOCS2K promoted synthesis of substituted benzils from diphenylacetylene derivatives

A facile protocol is described for the synthesis of benzil derivatives from readily accessible diarylacetylene derivatives using the NH₄I/EtOCS₂K system. This novel protocol results in excellent chemoselectivity and provided good to excellent yields. A control experiment indicated that the reaction proceeds via NH₄I promoted EtOCS₂K dimerization to give the corresponding dixanthogen and subsequent dixanthogen assisted oxidation.     

Cyclisation of benzils

Treatment of several substituted benzils [3,3′- and 4,4′-dimethyl-; 2,2′-, 3,3′- and 4,4′-dichloro-; 3,3′-dibromo-; 4-(N,N-dimethylamino)-] with an excess of chlorosulfonic acid gave the corresponding 3-chloro-2-phenylbenzofuran disulfonyl dichlorides. Disubstitution was confirmed by microanalytical and spectral data for the corresponding bis(N,N-dimethylaminsulfonamides). The positions of electrophilic substitution were not confirmed with 3,3′-dimethyl-, 2,2′- and 3,3′-dichlorobenzils. With 4,4′-dichlorobenzil, a smaller amount of chlorosulfonic acid enabled the isolation of 3,6,4′-trichloro-2-phenylbenzofuran-5-sulfonyl chloride, which was identified by X-ray analysis of the N,N-dimethylsulfonamide. The cyclisation failed with 3,3′-dimethoxy-, and 3,3′- and 4,4′-dinitrobenzils. The results have been interpreted mechanistically.     

The loss of ortho halogeno substituents from substituted thiobenzamide ions

The loss of ortho substituents (CH₃, Cl, Br, I) from molecular ions of substituted thiobenzamides has been investigated by determination of the critical energy and kinetic energy released during this process to obtain some further insight into the corresponding reaction of N,N-dimethylthiobenzamide ions. In contrast to the latter compounds the ortho methyl substituent is not eliminated from the molecular ions of o-methylthiobenzamide, but the loss of ortho halogeno substituents occurs with identical reaction characteristics in both series of compounds. It is concluded that the loss of halogeno substituents from molecular ions in both series corresponds to a direct substitution reaction via a 4-membered transition state.     

Unsymmetrically substituted N-heterocyclic phosphenium ions

Reduction of an unsymmetrically substituted α-diimine followed by condensation with PCl₃ yielded a P-chloro-N-aryl-N′-alkyl diazaphospholene which was further converted into an unsymmetrical diazaphospholium triflate by reaction with trimethylsilyl triflate. Reaction of tetramers of N-H- or N-alkyl-benzo-1,3,2-diazaphospholes with methyl triflate or triflic acid led in one step to triflate salts of unsymmetrically substituted benzo-1,3,2-diazaphospholium cations. Determination of the crystal structures of two of these derivatives by single-crystal X-ray diffraction studies revealed that individual cations and anions in the crystal lattice interact via specific electrostatic, π-stacking, or van-der-Waals type interactions to form supramolecular assemblies. Thermoanalytical measurements disclosed that benzo-diazaphospholium triflates with medium length alkyl chains melt below 100 °C and exhibit a strong tendency to form supercooled liquids.     

A survey of some theoretical studies of negative ions

The quantum chemical methods employed by us to investigate the stabilities, charge densities, and bonding characteristics of atomic and molecular anions are briefly reviewed. The results of our work on chemically interesting species are surveyed, as are our initial results on the treatment of solvation effects in anionic systems. Finally, a simple-minded approach to the problem of finding shape resonances for electron–atom scattering processes is outlined.     

Dynamic polarizability of negative ions

Theoretical and Experimental Chemistry -     

Polarizability of negative molecular ions

Theoretical and Experimental Chemistry -     

A theoretical investigation of charge transfer in several substituted acridinium ions

We present calculations for various properties of the ground and excited states of several arylamine-substituted acridinium ion systems that have been studied experimentally. Using ab initio and semiempirical quantum mechanical methods together with the generalized Mulliken-Hush (GMH) model, we examine the excitation energies, dipole moment shifts, and electronic coupling elements for the vertical charge shift (CSh) processes in these systems. We also examine solvent effects on these properties using a dielectric continuum reaction field model. The results are in generally good agreement with available experimental results and indicate that there is strong electronic coupling in these systems over a wide range of torsional angles. Nevetheless, the initial and final cationic states remain reasonably well-localized over this range, and thus TICT state formation is unlikely in these systems. Finally, a version of the GMH model based on Koopmans' Theorem is developed and found to yield coupling elements generally within a factor of 2 of the many-electron GMH for a sample acridinium system, but with overestimated adiabatic and diabatic dipole moment differences.     

Hartree-Fock theory for negative ions

It is shown that HF computations which yield ?_i > 0 for an occupied MO do not minimize the HF energy. If ?_i > 0, which frequently occurs in the RHF treatment of negative ions, one can reduce ?_i to zero and simultaneously lower E_HF by an appropriate admixture of a continuum function to the corresponding MO ?. We propose a modification of the HF model that takes these facts into account. Applications to the systems O^2?, N^3?, C^4?, S^2?, O₂^2?, C₂^2? are reported and discussed.     

Mass spectra of negative ions from thiophane and its alkyl derivatives

The mass spectra of the negative ions from the dissociative capture of electrons were obtained for thiophane and its alkyl derivatives. With a few exceptions, all of these negative ions of the spectrum contain sulfur atoms: electron capture is not observed in cyclic compounds — cyclopentane and methylcyclopentane. The principle routes of dissociation during electron capture were isolated for thiophane and alkylthiophanes and explain the greater portion of the observed lines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1631–1632, December, 1971.     

A collisional activation study of ions generated from the molecular ions of 2-phenoxyethyl halides

Collisional activation spectra of ions generated from phenol, [2,2,2]oct-2-en-5,7-dione and site specifically deuterium labelled 2-phenoxyethyl halides, , have shown that 2,4-cyclohexadienone and phenol ions are distinct stable species in the gas phase for ≥ 10^?5 s.     

Photoelectron spectroscopic study of the negative ions of 4-thiouracil and 2,4-dithiouracil

We report the photoelectron spectra of the negative ions of 4-thiouracil (4-TU)(-) and 2,4-dithiouracil (2,4-DTU)(-). Both of these spectra are indicative of valence anions, and they are each dominated by a single broad band with vertical detachment energies of 1.05 and 1.4 eV, respectively. Complementary calculations by Dolgounitcheva, Zakrzewski, and Ortiz (see companion paper) are in accord with our experimental results and conclude that the (4-TU)(-) and (2,4-DTU)(-) anions, reported herein, are valence anions of canonical 4-thiouracil and canonical dithiouracil. Comparisons among the anions and corresponding neutrals of 4-thiouracil, 2,4-dithiouracil, 5-chlorouracil, 5-fluorouracil, and uracil itself show that both sulfur and halogen modifications of uracil give rise to significant changes in the electronic structure. The electron affinities of the first four are all substantially larger than that of the canonical uracil.     

Spectral study of the conversion of porphyrins during interaction with molecular negative ions

In the interaction of ethioporphyrin and of several of its metal derivatives with negative ions of pyridine and anthracene in tetrahydrofuran solutions, an electron transfer takes place which results in the conversion of the pyridine and anthracene ions into neutral molecules, whereas the molecules of the pigment are first transformed into monovalent anions and subsequently into the di-, tri-, tetra-, and sometimes even into the hexavalent anions. In the first stage of this interaction, ferriethioporphyrin is reduced to ferro-ethioporphyrin, whereas the unmetallized pigment and its copper complex are transformed into the disodium derivative of ethioporphyrin. When the temperature is lowered, the rate of the electron transfer from pyridine ions to zinc-ethioporphyrin is decreased, and illumination leads to a substantial rate increase. The photochemical sensitivity of this system is possibly linked to the formation of stable complexes between pigment molecules and pyridine ions.     

Reaction of ethyl bromoacetate with substituted naphthoate ions

Rate constants for the reaction of ethyl bromoacetate with three series of substituted naphthoate ions have been measured in an acetone-water mixture (90% v/v). Using σ _p values rate constants at 30^o correlate well with the Hammett equation yielding ρ=−0.54, −0.19 and −0.25 for (4,1−), (6,1−) and (6,2−) series, respectively. Comparison of these ρ values with those of the reaction of phenacyl bromide reveals the failure of the reactivity-selectivity principle RSP in these reactions. Failure of RSP has been explained in terms of isoselective temperature.