Quantum chemical calculations of hydration electrostatics and electrochemical oxidation potential of cyclic nitroxide radicals

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Quantum chemical calculations on thioridazine

Quantum chemical CNDO /2 calculations for the conformational preference of the side chain of thioridazine as a function of angle indicated the crystallographically determined structure gave the lowest energy. There is also a small region of conformational flexibility within the first 90° of rotation of the side chain. This is commensurate with the results which we had obtained previously for our similar calculations for promazine and its Cl and CF₃ derivatives, perazine and its Cl and CF₃ derivatives, and for the hypothetical hitherto unknown N-piperidinopromazine and its Cl and CF₃ derivatives. The conformational profile of thioridazine resembles that of the perazines. The calculated gross atomic populations on the alkyl nitrogen in thioridazine was within the range we had previously found necessary for neuroleptic activity.     

Quantum chemical calculation of hydration for alkali metal salts

Calculations using the GAUSSIAN 03 program package were performed to determine the hydrated structures of lithium, potassium, LiCl, NaCl, and sulfonic cation exchanger in the form of alkali metal ions. For ions with positive hydration, the distance between the radii of the first and second spheres of hydration water is larger than in pure water; for ions with negative hydration, this distance is smaller. Salts with different types of hydration for cation and anion have hydrated structures similar to those of ions with negative hydration.     

Separation of aliphatic and aromatic amines by thin-layer chromatography using silica gel plates

Summary 28 different aromatic and aliphatic amines have been separated by TLC; 20 solvent systems were examined.     

Kinetics and mechanism of the deamination of primary aliphatic amines on the silica surface

Temperature-programmed desorption mass spectrometry was used to study the reaction of a series of primary amines (isobutylamine, isopentylamine, 1-pentylamine, 1-hexylamine, and 1-heptylamine) with a fumed silica surface. A mechanism was proposed and the kinetic parameters of the formation of alkenes from the chemisorbed aliphatic amine fragments on the silica surface were determined. A linear correlation was found between the activation energy and Taft constants for the substituents at the reaction site.     

Quantum chemical calculations for polyvinylidene fluoride with substitution defects

The MNDO calculation method and molecular cluster model are used to study the influence of substitution defects formed by alkali metal (Li, Na, K) and halogen (Cl, I) atoms on the saturation polarization and forbidden gap of polyvinylidene fluoride (CH₂2CF₂) a pyroelectric with pronounced photoelectric properties. Densities of state are calculated for both the defectless pyroelectric and for the sample with substitution defects. The calculated energy characteristics are in good agreement with the available experimental data. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 3, pp. 468-473, May–June, 2000.     

Quantum chemical calculations of fluoroethylene molecules by the CNDO and INDO methods

Conclusions A quantum chemical calculation of seven fluoroethylene molecules and two fluorochloroethylene molecules and two fluorochloroethylene molecules by the CNDO and INDO methods has made it possible to explain the experimentally observed change in reactivity and direction of addition reactions at the double bond. The data of a calculation of the relative stability of various isomers also agree with the experimental results.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2199–2202, October, 1973.     

Correlation between basicity and quantum chemical indices of some aliphatic amines

Conclusions The change in the pK values of solutions of aliphatic amines (C₂H₅)₂NCH₂CH₂X in acetic acid is linear and opposite to the change in the energies of the upper filled molecular orbitals, which were calculated by the CNDO/2 method.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1908–1909, August, 1979.The authors are indebted to L. A. Piruzyan for his constant interest in the work.     

Semiempirical calculations of ESCA chemical shifts by the SCC-AMEP model

ESCA chemical shifts give a direct insight into the charge redistribution accompanying formation of chemical bonds. This remarkable feature follows directly from a finding that inner-shell binding energies are closely related to the potentials exerted on the nuclei in question. We have provided extensive evidence which conclusively shows that electrostatic potentials (EP), evaluated in the atomic monopole (AM) approximation, by using the self-consistent charge (SCC-MO) densities, reproduce observed ESCA data in a surprisingly successful way. This approach, abbreviated heretofore the SCC-AMEP model, has also a considerable predictive power. The results have usually an accuracy which is placed in between the chemical and moderate precision. Hence, the salient features of the basic ESCA lines are well described within the AMEP approximation. Finally, the role of the relaxation energy is briefly discussed.     

Quantum chemical calculations on the catalytic dehydration of 2-propanol

The charge on atoms and the bond strengths in CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– and CH₃ CH₃...O(H)CH(CH₃)₂ have been calculated by the CNDO/2 method. The results are in agreement with published experimental observations on catalytic dehydration. A modified mechanism of anti-elimination on solid catalysts is proposed.

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CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– CH₃ CH₃...O(H)CH(CH₃)₂, CNDO/2. . .

     

Quantum chemical ab initio calculations for excited states of F IV

Quantum chemical ab initio calculations have been performed for the ground state and for several excited states of the F³⁺ ion (F IV). Three levels of accuracy have been used: Frozen-core SCF calculations (FRC-SCF) to determine orbital energies ε _nl and quantum defects δ _l for excited Rydberg orbitalsnl; frozen-core SCF followed by CI calculations (FRC-CI) which account for multiplet splittings and configuration mixings, and multi-configuration coupled-electron-pair approximation (MC-CEPA) calculations which include dynamic correlation effects. The accuracy of the calculated excitation energies is in the order of 5000 cm^?1 at the FRC-CI level and in the order of 500 cm^?1 at the MC-CEPA level. This latter error amounts to about 0.1% for excitation energies in the range of 400000 to 600000 cm^?1. The MC-CEPA calculations have been performed for 17 experimentally known states and for 14 experimentally unknown states, in particular for the configurations 2s2p ² (² D)3s, 2s 2p ²(² S)3s, 2s ² 2p 4p, and 2s ² 2p 5p.     

CNDO/2 molecular orbital calculations on the complexes formed between dimethylberyllium and aliphatic amines

A systematic CNDO/2 study has been carried out on the molecular complexes formed between dimethylberyllium and aliphatic amines. It has shown that the calculated molecular properties of these complexes, viz. the interaction energy, amount of charge transferred and the enhancement of the dipole moment are related to the ionization potential of the amine. The results are discussed in terms of the Mulliken's charge transfer theory.     

pKa calculations of aliphatic amines, diamines, and aminoamides via density functional theory with a Poisson-Boltzmann continuum solvent model

In order to make reliable predictions of the acid-base properties of macroligands with a large number of ionizable sites such as dendrimers, one needs to develop and validate computational methods that accurately estimate the acidity constants (pKa) of their chemical building blocks. In this article, we couple density functional theory (B3LYP) with a Poisson-Boltzmann continuum solvent model to calculate the aqueous pKa of aliphatic amines, diamines, and aminoamides, which are building blocks for several classes of dendrimers. No empirical correction terms were employed in the calculations except for the free energy of solvation of the proton (H+) adjusted to give the best match with experimental data. The use of solution-phase optimized geometries gives calculated pKa values in excellent agreement with experimental measurements. The mean absolute error is <0.5 pKa unit in all cases. Conversely, calculations for diamines and aminoamides based on gas-phase geometries lead to a mean absolute error >0.5 pKa unit compared to experimental measurements. We find that geometry optimization in solution is essential for making accurate pKa predictions for systems possessing intramolecular hydrogen bonds.     

Quantum chemical calculations of the structure of hydrogen-bonded sulfuric acid-dimethylformamide complexes

The most characteristic structures of hydrogen-bonded (H₂SO₄)₂, H₂SO₄-dimethylformamide (DMF) and (H₂SO₄)₂-DMF complexes are obtained by means of B3LYP/cc-pVQZ. The changes in the geometric parameters of the complexes are analyzed and the energy values of the intermolecular interaction are estimated. The electronic mechanism for the formation of hydrogen bonds between molecules is considered. It is shown that complexes of (H₂SO₄)₂-DMF composition are more energy-stable than complex with one H₂SO₄ molecule. It is established that molecular complexes with very strong hydrogen bonds and complexes with proton transfer can be formed between an acid dimer and N,N-dimethylformamide. It is concluded that protons can be transferred in the gas phase in (H₂SO)₂-DMF, where the molecules in (H₂SO₄)₂ are bound by three hydrogen bonds.