The estimation of the aromaticity of five-membered and benzo fused five-membered rings by the hybrid DFT computed magnetic properties

The structures of thiophene, pyrrole, furan, and their benzo derivatives were generated with the hybrid B3LYP density functional theory (DFT) methods employing a 6-31G* basis set. Their magnetic susceptibility anisotropics were calculated on these geometries with a continuous set of gauge transformations. The aromaticity of the heterocycles was discussed in light of their structural uniformity and magnetic susceptibility. The computed structural parameters, order of aromaticity, stability, and reactivity is in excellent agreement with the experimental results. The usefulness of this approach to determine the reactivity is discussed.     

Complete basis set ab initio computational study of ionization potential, electron affinity and the C-F bond dissociation energy for perfluorinated methane derivatives

A computational study of perfluorinated methane derivatives was performed with complete basis set ab initio methods. The total energies for their neutral, cation, and anionic states were computed. From these values, the energy gaps between different electronic states, ionization potentials, electron affinities, and C-F bond dissociation energies were calculated. The computed values are compared with experimental data and the reliability of complete basis set ab initio methods is discussed. New values for C-F bond dissociation energies are suggested. Received: 12 January 1998 / Accepted: 2 April 1998 / Published online: 29 July 1998     

Ligand free open air copper(II) mediated aryl formamidation and amination of aryl halides

A simple synthetic procedure for direct formamidation and amination of aryl halides mediated by copper(II) salts was developed in open air, without an external ligand in formamide with potassium carbonate as a base. This approach is particularly efficient when electron active aryl halides are used as substrates. In these cases almost quantitative formamidation was observed.     

Unique charge-separated pyridinium-barbituric acid zwitterions

A synthetic procedure for the preparation of the unusual charge-separated pyridinium barbiturate zwitterion 2 from 1,3-dimethylbarbituric acid and 2-pyridinecarbaldehyde in methanol was developed. The structure of the compound was confirmed with X-ray analysis to demonstrate the strong charge separation throughout the molecule. One would expect that this charge separation would increase its reactivity; however, contrary to this expectation, the compound is very stable in acidic media, and in the presence of a base, decarbonylation occurs on one barbituric acid while the zwitterionic moiety of the molecule stays intact.     

Microwave-assisted synthesis of 1,3-benzodioxole derivatives from catechol and ketones or aldehydes

An efficient synthetic procedure for the preparation of a diverse library of 1,3-benzodioxoles was developed by applying controlled microwave heating in comparison with currently available conventional heating. Reactions were completed in less than 3 h. The isolation of product is simple, the isolated yields are good to excellent, and this method is applicable to large scale production.     

Ab initio and density functional theory studies of the gas-phase hydrogen fluoride addition to ethylene. An example of catalytic effect from a second molecule of the reagent

The accuracy of three popular DFr methods (hybrid, gradient-corrected, and local) has been evaluated on the HF-assisted addition of HF to ethylene. The possibility of forming trimolecular (two HF and one ethylene) and dimolecular (one HF and one ethylene) complexes and transition state structures during the transformation of HF and ethylene in fluoroethane is discussed. An energetically favorable pathway was selected on the basis of the computed potential energy surface for these two reactions.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Density functional theory study of difluorovinylidene isomerization to difluoroacetylene

The isomerization of difluorovinylidene: C = CF₂ into difluoroacetylene FCCF was systematically studied using density functional theory (DFT) methods with the 6-311 + G(2 p, 2 p) Gaussian-type basis set. The computed geometries for the reactant, product, and transition state as well as the enthalpy and reaction barrier were compared with the previously computed values obtained by the LSD and NLSD DFT methods and the ab initio CCSD method. The suitability of some of the DFT methods for the computation of this system was discussed and the best estimated computational data were selected. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 515–520, 1997     

Complete basis set, the MP2 ab initio, and hybrid density functional theory evaluation of ionization potential and electron affinity for PH, PH2, PHF, PF, and PF2

A systematic study was performed on the small molecular systems built from phosphor, hydrogen and fluorine with the target being to evaluate accurately their ionization potentials and electron affinities, as well as influence fluorine on the ionization potential of phosphor as a central atom. To determine the accuracy of hybrid density functional methods for computing those energies, ionization energies for hydrogen, fluorine and phosphor were calculated and compared with the experimental and CBSQ values. To demonstrate the accuracy of this method, both the ionization potential and the electron affinity for phosphorus and fluorine atoms were calculated and compared with the experimental data. For both PF and PF₂, an identical electron affinity of 0.72 eV and for PH and PHF 1.0 eV were suggested.