Double-ionization energies to ground and excited states of the tungsten hexacarbonyl dication

Tungsten hexacarbonyl was investigated by double-charge-transfer (DCT) spectroscoPy, and the double-ionization energies to ground and electronically excited states of W(CO) ₆ ²⁺ determined. The double-ionization energies corresponding to the first two distinct peaks in the spectra are 22.8 ± 0.3 eV and 28.5 ± 0.3 eV, but numerous overlapping peaks at higher energies are evident. It is shown that the DeI spectra can explain the main features of a previously determined (J. Am. Soc. Mass Spectrom. 1990, 1, 16–27) internal energy distribution curve for W(CO) ₆ ²⁺ ions formed by 70-eV electron ionization of W(CO)₆ molecules.     

Enantioselective organocatalytic synthesis of fluorinated molecules

The enantioselective synthesis of fluorinated molecules has drawn much attention within the chemical community due to its unique stereoelectronic properties. The main aim of this review is to cover the most important organocatalytic enantioselective methodologies to obtain them. The review is divided into three parts: first, the direct introduction of a fluorine atom studied in the early 2000s. Second, the later use of Michael reactions to introduce fluorine-containing synthons. Finally, the simultaneously-developed trifluoromethylation reactions, giving the catalysts, mechanisms and reagents that have been used.     

Photophysics of fluorinated benzene. III. Hexafluorobenzene

A theoretical study of the photoabsorption spectroscopy of hexafluorobenzene (HFBz) is presented in this paper. The chemical effect due to fluorine atom substitution on the electronic structure of benzene (Bz) saturates in HFBz. State- of-the-art quantum chemistry calculations are carried out to establish potential energy surfaces and coupling surfaces of five energetically low-lying electronic (two of them are orbitally degenerate) states of HFBz. Coupling of these electronic states caused by the Jahn-Teller (JT) and pseudo-Jahn-Teller (PJT) type of interactions are examined. The impact of these couplings on the nuclear dynamics of the participating electronic states is thoroughly investigated by quantum mechanical methods and the results are compared with those observed in the experiments. The complex structure of the S(1) ← S(0) absorption band is found to originate from a very strong nonadiabatic coupling of the S(2) (of πσ* origin) and S(1) (of ππ* origin) state. While S(2) state is orbitally degenerate and JT active, the S(1) state is nondegenerate. These states form energetically low-lying conical intersections (CIs) in HFBz. These CIs are found to be the mechanistic bottleneck of the observed low quantum yield of fluorescence emission, non overlapping absorption, and emission bands of HFBz and contribute to the spectral width. Justification is also provided for the observed two peaks in the second absorption (the unassigned "c band") band of HFBz. The peaks observed in the third, fourth, and fifth absorption bands are also identified and assigned.     

Activation energies in catalytic oxidation of benzene

The existence of a linear correlation between the apparent activation energy of benzene disappearance and the primary selectivity was demonstrated for a series of vanadia based catalysts. Analysis of this correlation leads to the conclusion that the activation energies of reaction 1 as well as activation energies of reaction 2 in benzene oxidation scheme do not differ significantly over a series of these catalysts.

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High levelab initio stabilization energies of benzene

Summary G2 theory is shown to be reliable for calculating isodesmic and homodesmotic stabilization energies (ISE and HSE, respectively) of benzene. G2 calculations give HSE and ISE values of 92.5 and 269.1 kJ mol^–1 (298 K), respectively. These agree well with the experimental HSE and ISE values of 90.5±7.2 and 268.7±6.3 kJ mol^–1, respectively. We conclude that basis set superposition error corrections to the enthalpies of the homodesmotic or isodesmic reactions are not necessary in calculations of the stabilization energies of benzene using G2 theory. The calculated values of the enthalpies of formation of such molecules containing multiple bonds such as benzene ands-trans 1,3-butadiene, which are found from the enthalpies of isodesmic and homodesmotic reactions rather than of atomization reactions, demonstrate good performance of G2 theory. Estimates of theH _f ^o value for benzene from the G2 calculated enthalpies of homodesmotic reaction (2) and isodesmic reaction (3) are 80.9 and 82.5 kJ mol^–1 (298 K), respectively. These are very close to the experimentalH _f ^o value of 82.9±0.3 kJ mol^–1. TheH _f ^o value ofs-trans 1,3-butadiene calculated using the G2 enthalpy of isodesmic reaction (4) is 110.5 kJ mol^–1 and is in excellent agreement with the experimentalH _f ^o value of 110.0±1.1 kJ mol^–1.     

Relative energies of substituted benzene valence isomers

Ab initio calculations employing the STO-3G basis set are used to obtain the relative energies of the benzene valence isomers and some selected monosubstituted derivatives. We find that 3,3'-bicyclopropenyl, the least stable of the five (CH)₆ examined, is slightly more stable in the anti conformation than the gauche (Φ = 45°) conformation in agreement with experiment. Substituents are calculated to produce significant changes in the relative energies of the benzene valence isomers. The ground-state isomerization of 1-Dewar benzeneearbinyl cation to benzyl cation is more exothermic than the aromatization of Dewar benzene, but is, in contrast to the latter, symmetry-allowed.     

Empirical resonance energies for benzene and pyridine

Empirical resonance energies are calculated for benzene and pyridine from both experimental ΔH_f^o data and from total molecular energies obtained using the 6-31G* basis set as the energy change for three distinct types of reaction. The results show that the aromatic stabilization of pyridine and benzene is essentially the same.     

Alkali-ion microsolvation with benzene molecules

The target of this investigation is to characterize by a recently developed methodology, the main features of the first solvation shells of alkaline ions in nonpolar environments due to aromatic rings, which is of crucial relevance to understand the selectivity of several biochemical phenomena. We employ an evolutionary algorithm to obtain putative global minima of clusters formed with alkali-ions (M(+)) solvated with n benzene (Bz) molecules, i.e., M(+)-(Bz)(n). The global intermolecular interaction has been decomposed in Bz-Bz and in M(+)-Bz contributions, using a potential model based on different decompositions of the molecular polarizability of benzene. Specifically, we have studied the microsolvation of Na(+), K(+), and Cs(+) with benzene molecules. Microsolvation clusters up to n = 21 benzene molecules are involved in this work and the achieved global minimum structures are reported and discussed in detail. We observe that the number of benzene molecules allocated in the first solvation shell increases with the size of the cation, showing three molecules for Na(+) and four for both K(+) and Cs(+). The structure of this solvation shell keeps approximately unchanged as more benzene molecules are added to the cluster, which is independent of the ion. Particularly stable structures, so-called "magic numbers", arise for various nuclearities of the three alkali-ions. Strong "magic numbers" appear at n = 2, 3, and 4 for Na(+), K(+), and Cs(+), respectively. In addition, another set of weaker "magic numbers" (three per alkali-ion) are reported for larger nuclearities.     

Gelation of fluorinated liquids by non-fluorinated low-molecular-mass molecules

A family of tetrahydroxy diesters has been synthesised and observed to gel a range of fluorinated solvents and their mixtures; the phase behaviour and gel microstructure are reported for a homologous family of these diesters in blends of 1H,1H-heptafluorobutanol (HFB) and 2H,3H-perfluoropentane (HPFP).     

Accurate ab initio binding energies of the benzene dimer

Accurate binding energies of the benzene dimer at the T and parallel displaced (PD) configurations were determined using the single- and double-coupled cluster method with perturbative triple correction (CCSD(T)) with correlation-consistent basis sets and an effective basis set extrapolation scheme recently devised. The difference between the estimated CCSD(T) basis set limit electronic binding energies for the T and PD shapes appears to amount to more than 0.3 kcal/mol, indicating the PD shape is a more stable configuration than the T shape for this dimer in the gas phase. This conclusion is further strengthened when a vibrational zero-point correction to the electronic binding energies of this dimer is made, which increases the difference between the two configurations to 0.4-0.5 kcal/mol. The binding energies of 2.4 and 2.8 kcal/mol for the T and PD configurations are in good accord with the previous experimental result from ionization potential measurement.     

Solvation energies of planar and pseudo-planar molecules

The Born equation for solute-solvent interaction is generalized to planar and pseudo-planar molecules. The solvation energies thus obtained are compared to experimental values and the agreement is satisfactory.     

Magnetic resonance energies of heterocyclic conjugated molecules

Magnetic resonance energy (MRE), derived from ring-current diamagnetic susceptibility, can be interpreted as a kind of aromatic stabilization energy. For polycyclic conjugated hydrocarbons, this quantity correlates well with topological resonance energy (TRE). MREs for typical heterocyclic conjugated molecules were then calculated and analyzed. It was found that even for heterocycles MRE highly correlates with TRE. Thus, the MRE concept has been firmly established as a reliable indicator of aromaticity, which mediates magnetic criteria of aromaticity with energetic ones. The conformity of heterocycles to the rule of topological charge stabilization can be checked using not only TRE but also MRE.     

Calculation of bond energies in diatomic molecules

Theoretical Chemistry Accounts - An extrapolation method is proposed for an approximative evaluation of covalent bonding powers of some elements from their electronegativity values. Using these...     

Pseudo-Raman broad band of stacked benzene molecules

The broad band displayed by pilled-up benzene molecules in Raman-like scale has the same nature as the one produced by chain polymers as BSA and PGA.     

Reaction of quinolines fluorinated at the benzene ring with nitrogen-centered nucleophiles

A primary functionalization of quinolines polyfluorinated at the benzene ring (5,7-difluoro-, 5,7,8-trifluoro-, 5,6,8-trifluoro-, 8-chloro-5,7-difluoro-, 5,6,7,8-tetrafluoro-, and 5,7,8-trifluoro-6-(trifluoromethyl)quinolines) by the reaction with nitrogen-centered nucleophiles (aqueous and liquid ammonia, hydrazine hydrate, piperidine) has been studied. If the molecule of fluorinated quinoline contains three or four halogen atoms, their combined orientation effect outweighs the influence of the heterocycle N atom. It was found that the orientation of substitution in the reactions of 5,6,8-trifluoro- and 5,7,8-trifluoro-6-(trifluoromethyl)quinolines with piperidine depends on temperature, because the enthalpy control of the ratio of the rates of competing reactions changes to the entropy control. Nineteen new quinoline derivatives containing F atoms and amino or modified amino groups in the benzene ring have been obtained.     

Graph-theoretical resonance energies of benzene and heterobenzenes from photoelectron spectra

Experimental values of π ionization potentials, non-subjective linear regression techniques, and graph theory are used to calculate resonance energies with the results, C₆H₆, 0.821 eV; C₆H₅N, 0.618 eV; C₆H₅P 0.661 eV; C₆H₅As, 0.545 eV; C₆H₅Sb, 0.607 eV.     

On unicyclic conjugated molecules with minimal energies

The energy of a graph is defined as the sum of the absolute values of all the eigenvalues of the graph. Let U(k) be the set of all unicyclic graphs with a perfect matching. Let C _g(G) be the unique cycle of G with length g(G), and M(G) be a perfect matching of G. Let U ⁰(k) be the subset of U(k) such that g(G)≡ 0 (mod 4), there are just g/2 independence edges of M(G) in C _g(G) and there are some edges of E(G)\ M(G) in G\ C _g(G) for any G∈U ⁰(k). In this paper, we discuss the graphs with minimal and second minimal energies in U ^*(k) = U(k)\ U ⁰(k), the graph with minimal energy in U ⁰(k), and propose a conjecture on the graph with minimal energy in U(k).      

Aqueous solubilization of highly fluorinated molecules by semifluorinated surfactants

The physical and chemical properties of organic compounds are deeply affected by the introduction of fluorinated substituents. Perfluorinated and highly fluorinated organic molecules are both hydrophobic and lipophobic. This makes the recognition and the binding of fluorinated molecules extremely difficult to achieve through classical elements of molecular recognition. Here we show that semifluorinated water-soluble block copolymers can generate micellar structures having a fluorous phase-based inner core in aqueous solution. Furthermore, we show that these micelles can be used to encapsulate and bind highly fluorinated molecules through association in the internal fluorous phase (fluorophobic effect). We report that semifluorinated block copolymers can be used for the aqueous solubilization of the widely diffused gaseous anesthetic sevoflurane, thereby suggesting the possibility of the intravenous delivery of this commonly used anesthetic.     

Surface energies of chain molecules from homogeneous nucleation

A model for the interpretation of homogeneous nucleation data for chain molecules is presented. The two surface energies σ_s and σ_e are related to interchain and intrachain bonding. Surface energies calculated from experimental data on n-alkanes from octane to dotriacontane and polyethylene agree with estimated values. The results are discussed in relation to surface energies measured from spherulite growth rates in polymers but these values are not known with sufficient reliability to provide a good basis for comparison.