Molecular Mimicry of Structure and Electron Density Distributions in Minerals

1986 ◽  
Vol 73 ◽  
Author(s):  
G. V. Gibbs ◽  
M. B. Boisen
Keyword(s):  
Bond Strength ◽  
Electron Density ◽  
Molecular Orbital ◽  
Computational Models ◽  
Molecular Mimicry ◽  
Strength Parameter ◽  
Molecular Orbital Calculations ◽  
Bond Lengths ◽  
Density Distributions ◽  
Reaction Energies

ABSTRACTMolecular orbital calculations on hydroxyacid molecules with first- and secondrow X-cations (X = Li through N and Na through S) yield bond lengths and angles that mimic those of chemically similar minerals. These bond lengths are used to find a formula giving bond length as a function of a bond-strength parameter that reproduces XO bond lengths in crystals with main-group X-cations from all six rows of the periodic table within 0.05Å on average. The molecular orbital calculations also provide insights into reaction energies, physical properties of crystals such as electron density distributions, and data not amenable to direct measurement. They also provide a basis from which computational models for mineral structures may be constructed.

The stabilization of alkoxide anions

1969 ◽  
Vol 47 (12) ◽  
pp. 2306-2307 ◽  
Author(s):  
N. C. Baird
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Cyclotron Resonance ◽  
Molecular Orbital Calculations ◽  
Ion Cyclotron Resonance ◽  
Density Distributions ◽  
Alkyl Groups ◽  
Valence Electrons ◽  
Ion Cyclotron

Molecular orbital calculations by the MINDO method are reported for the valence electrons of HO− and a number of small alkoxide anions. The acidity order [Formula: see text] is predicted, in agreement with recent ion cyclotron resonance studies. The electron density distributions within the ions are discussed with reference to current models of the polarizability of alkyl groups.

Molecular orbital structures of sulfones

1982 ◽  
Vol 60 (6) ◽  
pp. 730-734 ◽  
Author(s):  
Russell J. Boyd ◽  
Jeffrey P. Szabo
Keyword(s):  
Crystal Structure ◽  
Gas Phase ◽  
Molecular Orbital ◽  
Geometry Optimization ◽  
Membered Ring ◽  
Molecular Orbital Calculations ◽  
Bond Lengths ◽  
Comparison With Experiment ◽  
The Difference

Abinitio molecular orbital calculations are reported for several cyclic and acyclic sulfones. The geometries of XSO2Y, where X, Y = H, F, or CH3 are optimized at the STO-3G* level. Similar calculations are reported for the smallest cyclic sulfone, thiirane-1,1 -dioxide, as well as the corresponding sulfoxide, thiirane-1-oxide, and the parent sulfide, thiirane. Where comparison with experiment is possible, the agreement is satisfactory. In order to consider the possibility of substantial differences between axial and equatorial S—O bonds in the gas phase, as observed in the crystal structure of 5H,8H-dibenzo[d,f][1,2]-dithiocin-1,1-dioxide, STO-3G* calculations are reported for a six-membered ring, thiane-1,1-dioxide, and a model eight-membered ring. Limited geometry optimization of the axial and equatorial S—O bonds in the chair conformations of the six- and eight-membered rings leads to bond lengths of 1.46 Å with the difference being less than 0.01 Å.

scholarly journals Étude théorique de la structure du phosphate d'isaxonine

1984 ◽  
Vol 62 (4) ◽  
pp. 680-686
Author(s):  
Jean-Pierre Monti ◽  
Marcel Sarrazin ◽  
Pierre Brouant
Keyword(s):  
Chemical Shift ◽  
Molecular Orbital ◽  
Coupling Constants ◽  
Published Data ◽  
Molecular Orbital Calculations ◽  
Good Prediction ◽  
Proton Chemical Shift ◽  
Screening Constant ◽  
Bond Lengths ◽  
Bond Indices

Protonations of isaxonine phosphate are studied by performing CNDO/2 and CNDO/S molecular orbital calculations. Results are compared with previously published data. Wiberg's bond indices and S character percentages calculated using electronic populations are shown to correctly predict variations of bond lengths and bond angles as well as [Formula: see text] coupling constants. A good prediction of proton chemical shift variations using a calculation of the screening constant was obtained.

Substitutent Effects on the Geometrical Properties of 1-Phenylallyl Alcohol

2005 ◽  
Vol 60 (4) ◽  
pp. 265-270
Author(s):  
Salim Y. Hanna ◽  
Salim M. Khalil ◽  
Moafaq Y. Shandala
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Substituent Effects ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Molecular Orbital Calculations ◽  
Electron Densities ◽  
Geometrical Properties ◽  
Stabilization Energies

Abstract Optimized geometrical parameters, electron densities, heats of formation and stabilization energies have been obtained on X-substituted phenylallyl alcohols, where X is H, OCH3, NH2, CN, F and CH3 at ortho, meta, and para positions, using MINDO-Forces SCF-molecular orbital calculations. The substituent effects on the geometrical parameters and the electron density are discussed.

An investigation into the origins of polar substituent effects upon 19F chemical shifts, using 4-substituted β,β-difluorostyrenes

1980 ◽  
Vol 58 (8) ◽  
pp. 839-845 ◽  
Author(s):  
William F. Reynolds ◽  
Victoria G. Gibb ◽  
Nick Plavac
Keyword(s):  
Chemical Shift ◽  
Electron Density ◽  
Molecular Orbital ◽  
Excellent Agreement ◽  
Field Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Molecular Orbital Calculations ◽  
Chemical Shift Difference ◽  
Polar Substituent

19F, 13C, and 1H chemical shifts have been determined for β,β-difluorostyrene and eight 4-substituted derivatives. The β-fluorine chemical shift difference, ΔδF, is used to evaluate the constant in the Buckingham equation. A = 3.0 × 10−11 esu for C—F bonds which is in excellent agreement with the value derived by Adcock and Khor. This allows accurate estimates of direct field effect contributions to 19F chemical shifts in aryl fluorides. Substituent parameter correlations demonstrate that the primary polar effect on 19F chemical shifts is field-induced π polarization. Abinitio molecular orbital calculations confirm that the substituent-induced 19F chemical shifts reflect changes in fluorine π electron density.

Molecular Orbital Calculations on the Interaction of Ni and Cu Atoms with PN

1981 ◽  
Vol 36 (10) ◽  
pp. 1092-1094
Author(s):  
H. Itoh ◽  
G. Ertl
Keyword(s):  
Electron Transfer ◽  
Bond Strength ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Weak Interactions ◽  
Bond Formation ◽  
Molecular Orbital Calculations ◽  
Kcal Mole ◽  
Mo Calculations ◽  
Ab Initio Mo Calculations

Ab initio MO calculations for PN predict a pronounced electron transfer from the P to the N atom. Only very weak interactions result for M-PN (M = Ni, Cu) configurations whereas bond formation is predicted if the N atom couples to the metal. The bond strength for Ni (10.5 kcal/mole) is about twice as large as for the Cu-NP complex (4.6 kcal/mole). Coupling occurs mainly with the 7 σ-level (HOMO) of the ligand whose energy is lowered below that of the 2 π-level.

Electrophilic Substitution in Methyl-substituted Naphthalenes III. Correlation between Experimental Results and Molecular Orbital Calculations of Reactivity Indices

1971 ◽  
Vol 49 (24) ◽  
pp. 4073-4083 ◽  
Author(s):  
P. Canonne ◽  
Le-Khac Huy ◽  
W. Forst
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Predictive Value ◽  
Electrophilic Substitution ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Substrate Molecule ◽  
Simple Description ◽  
Reactivity Indices ◽  
Frontier Electron Density

Common reactivity indices (electron density qr,self-polarizability πrr, frontier electron density fr, superdelocalizability Sr, and localization energy Lr) are calculated for electrophilic substitution in 25 methyl-naphthalenes. An elementary s.c.f. method in the form of a modified ω-technique is used, using the hyperconjugative-heteroatom model for the methyl groups, with ω = 1.4, hx = 2.0, kc–x = 0.8. This choice gives reasonably good ionization potentials and very good correlation for singlet transitions (p-band) in u.v. spectra of α-methylnaphthalenes. Purely static indices qr, fr, and πrr are found to be unsuitable for predicting reactive positions for chloromethylation, while Sr and Lr are very satisfactory. On the theory that the polarizing effect of the approaching reagent is important, the index qr′ = qr + πrr δαr may be obtained, which is also found to be very satisfactory for δαr = β. If the interaction is viewed as an interaction between a hard acid (chloromethyl) and soft base (methylnaphthalenes), the index ΔEr = aqr + bfr is obtained, which is likewise found to be satisfactory with a = 1, b = 0.15. These results show clearly that it is insufficient to base reactivity considerations in methylnaphthalenes entirely on the properties of the isolated substrate molecule, but that even a very simple description of the substrate–reagent interaction is sufficient since the four indices Sr, Lr, qr′ and ΔEr all have the same predictive value.

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