Study of some aliphatic ammonium ylides by semiempirical and ab initio methods: Structure and charge distribution

1980 ◽  
Vol 45 (1) ◽  
pp. 92-103 ◽  
Author(s):  
Vladimír Král ◽  
Zdeněk Arnold
Keyword(s):  
Ab Initio ◽  
Charge Distribution ◽  
Quantum Chemical ◽  
Negative Charge ◽  
Dipole Moments ◽  
Ab Initio Methods ◽  
Chemical Methods ◽  
Quantum Chemical Methods

Structure of, and charge distribution in, some aliphatic ammonium ylides were determined by quantum chemical methods (CNDO/2, INDO, MINDO/2, PCILO, ab initio-STO-3G and 4-31G bases). Non-stabilized ylides were found to have pyramidal arrangement of bonds on the ylide carbon whereas the stabilized ylides have a planar arrangement. The charge distribution in stabilized ylides indicates a significant transfer of the negative charge from the ylide carbon to the electronegative groups. The calculated dipole moments for the previously prepared compounds, as well as for the derivatives VII and X, described in this paper, agree well with the experimental value.

Trimethylammoniodiformylmethylide: Structure and charge distribution

1980 ◽  
Vol 45 (1) ◽  
pp. 80-91 ◽  
Author(s):  
Vladimír Král ◽  
Zdeněk Arnold
Keyword(s):  
Dipole Moment ◽  
Total Energy ◽  
Ab Initio ◽  
Charge Distribution ◽  
Quantum Chemical ◽  
Energy Minimum ◽  
Chemical Methods ◽  
Quantum Chemical Methods ◽  
Total Energy Minimum

Geometric arrangement of trimethylammoniodiformylmethylide (I) and charge distribution in this compound were calculated by quantum chemical methods (EHT, CNDO/2, INDO, PCILO, MINDO/2, ab initio). Total energy minimum was found for the arrangement If. The experimentally found dipole moment agrees very well with that calculated for this conformation.

Quantum chemical study of sulfonium ylides: Structure, charge distribution and dipole moments

1980 ◽  
Vol 45 (4) ◽  
pp. 1236-1250 ◽  
Author(s):  
Vladimír Král ◽  
Zdeněk Arnold ◽  
Václav Jehlička ◽  
Otto Exner
Keyword(s):  
Ab Initio ◽  
Charge Distribution ◽  
Quantum Chemical ◽  
Dipole Moments ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Quantum Chemical Methods ◽  
Sulfonium Ylide ◽  
Experimental Values ◽  
Sulfonium Ylides

The geometry, charge distribution and dipole moments of parent sulfonium ylide - dimethylsulfoniomethylide (I) - and a series of stabilized sulfonium ylides, including 2-dimethylsulfuranylidene-1,3-cyclopentanedione (VI) prepared in this study, was investigated using the CNDO/2, PCILO and ab initio methods. Values of dipole moments, calculated by quantum chemical methods (CNDO/2 with sp and spd bases, ab initio with the STO-3G basis) as well as by the method of empirical bond moments, are compared with the experimental values determined in dioxane or benzene. Dipole moments of several related ammonium ylides were also studied.

scholarly journals How accurate are approximate quantum chemical methods at modelling solute–solvent interactions in solvated clusters?

2020 ◽  
Vol 22 (7) ◽  
pp. 3855-3866 ◽  
Author(s):  
Junbo Chen ◽  
Bun Chan ◽  
Yihan Shao ◽  
Junming Ho
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Interaction Energies ◽  
Chemical Methods ◽  
Dft Methods ◽  
Solvent Interactions ◽  
Quantum Chemical Methods ◽  
Composite Methods ◽  
Wide Range

In this paper, the performance of ab initio composite methods, and a wide range of DFT methods is assessed for the calculation of interaction energies of thermal clusters of a solute in water.

Tautomerism in Five-membered Nitrogen Heterocycles. A Test of the Reliability of Semiempirical (AMI, PM3, MNDO) Quantum Chemical Methods

1990 ◽  
Vol 45 (11-12) ◽  
pp. 1328-1334 ◽  
Author(s):  
Walter M. F. Fabian
Keyword(s):  
Quantum Chemical ◽  
Dipole Moments ◽  
Nitrogen Heterocycles ◽  
Ionization Potentials ◽  
Semiempirical Methods ◽  
Chemical Methods ◽  
Pm3 Method ◽  
Lone Pairs ◽  
Quantum Chemical Methods ◽  
The Stability

AbstractThe reliability of three popular semiempirical quantum chemical methods (AM1, PM3, MNDO) for the treatment of tautomeric equilibria is tested in a series of five-membered nitrogen heterocycles. The known flaw of MNDO to overestimate the stability of compounds with two or more adjacent pyridine-like lone pairs is also present in AM1 and to a somewhat lesser extent in PM3. Tautomeric species differing in the number of adjacent pyridine-like lone pairs, thus, cannot be adequately treated by these semiempirical methods. Both AM1 as well as PM3, however, represent major improvements over MNDO in the case of lactam-lactim tautomerism. The stability of N-oxides as compared to N-hydroxy tautomers seems to be overestimated by the PM3 method. All three semiempirical methods yield quite reliable ionization potentials and dipole moments.

scholarly journals Hydration dynamics gives the distinctive brown color in the "brown ring" nitrate test

2021 ◽  
Author(s):  
Ambar Banerjee ◽  
Michael R. Coates ◽  
Michael Odelius
Keyword(s):  
Aqueous Solution ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Solution Structure ◽  
Ab Initio Molecular Dynamics ◽  
Ring Test ◽  
Chemical Methods ◽  
Aqua Complexes ◽  
Quantum Chemical Methods ◽  
Ring Complex

The brown ring test is one of the most popular and visually appealing reagent tests, commonly known to chemistry undergrads and familiar even to school students. The exact composition, mechanism and structure of the complex has been investigated for nearly a century. Recent studies have elucidated its UV-vis, EPR and Mossbauer spectra, mechanistic details and kinetics, followed by crystallization and structure determination in solid state. Nonetheless these studies were unable to address the aspects of solution structure and dynamics of the brown ring complex. We have conducted ab initio molecular dynamics simulations of the classic brown ring complex in aqueous solution. In the process from the simulation trajectory, we have identified that the classically established pseudo-octahedral [Fe(H2O)5(NO)]2+ complex is in chemical equilibrium with the square-pyramidal [Fe(H2O)4(NO)]2+ complex through the exchange of one of the coordinated H2O molecules. The dynamics in aqueous solution between the penta-aqua and tetra-aqua complexes in the brown ring system has to our knowledge never been suggested earlier. Interestingly we find, using ab initio multi-reference quantum chemical methods i.e. CASSCF/NEVPT2 and CASPT2 calculations, that the mixture of these two complexes is what gives the distinctive brown coloration to the brown ring test. We show that its UV-vis spectrum can be theoretically reproduced only by accounting these two species, and not solely the classically established [Fe(H2O)5(NO)]2+ complex. The energetics of the penta-aqua and tetra-aqua complexes is also investigated at the level of multi-reference quantum chemical methods.

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