Treatment of hydrogen bonding within CNDO/2 and MINDO/3: CNDO/2H and MINDO/3H

A formalism has been developed to treat hydrogen-bonded A—H…?B systems within the CNDO /2 and the MINDO /3 methodologies. In this formalism the interactions are divided into three distinct classes; those between (a) two hydrogen-bonded atoms, (b) one hydrogen-bonded and non-hydrogen-bonded atom, and (c) two non-hydrogen-bonded atoms. The last class of interactions is treated solely by the existing CNDO /2 or MINDO /3 method. For A –H…?B systems, the core resonance integrals are individually parametrized depending upon the class of the interaction. Three types of A—H…?B systems have been thus far parametrized. Nine hydrogen-bonded dimers have been studied using the new formalism and the current CNDO /2 and the MINDO /3 methods. MINDO /3 predicts very large interatomic (A –B) distances for the equilibrium geometry, and relatively small stabilization values for the hydrogen-bond energies. CNDO/2 predicts the reverse. The new formalism for both CNDO /2 and MINDO /3 predicts accurate geometries as well as energies for all nine dimers. The new formalisms are called CNDO /2H and MINDO /3H. A general discussion of the nature of hydrogen bonding as exhibited by CNDO /2H and MINDO /3H is presented.     

MINDO/3 calculations of ESCA chemical shifts

Calculations of ESCA chemical shifts, using Jolly's equivalent core approximation and the MINDO/3 semi-empirical SCF MO method, have given results in reasonable agreement with experiment.     

MINDO/3 Calculation of carbocation heats of formation

Heats of formation calculated by MINDO /3 are reported for 42 carbocations for which experimental heats of formation have been published. Errors associated with these calculations can be large, with an overall range of ±13 kcal/mol. Correction of systematic errors in the MINDO /3 calculations by means of hydrocarbon models and isodesmic relationships results in a reduction in the range of errors to ±8 kcal/mol. Comparison with experimental heats of reaction of hydride transfer equilibria minimizes experimental errors and gives an average absolute error of 2 kcal/mol with a range of ±3 kcal/mol.     

A MINDO/3 MO study of oxidized flavins

The use of semi-empirical molecular orbital methods for the study of biologically important molecules has increased in recent years. The validity of well-known approximate Hartree-Fock molecular orbital methods such as MINDO/3 and MNDO still remains largely untested for biological molecules. Here we report its first application to the study of the electronic structures of isoalloxazines. Electronic charge distribution, variation of dipole moment, first ionization potential, electron affinity, orbital energies and electronic transitions are examined. Some of these results are compared with experiments. Good correlations with experiments were generally found in net atomic charge distributions, ionization potentials and electronic transitions. As a result of relatively good correlations with experiment application of the MINDO/3 method for extended study of biologically important coenzymes is promising.     

Development and status of MINDO/3 and MNDO

The historical development of MINDO/3 and MNDO is outlined in relation to the parallel developments of the ab initio SCF approach. It is pointed out that both treatments are purely empirical so far as chemistry is concerned and complement one another, MINDO/3 and MNDO allowing calculations to be carried out when ab initio methods of comparable performance are inapplicable because they need one-thousand times more computing time.     

Qualitative quantum-chemical models for surface OH groups of oxides

The dependence of the acidity and frequency characteristics of surface OH groups on the number and electronegativity of their bonded nonoxygen atoms has been analyzed in terms of the Del Re localized molecule orbitals method. The model suggested is applied, in particular, to interpret the nonmonotonous dependence of the stretching vibration frequencies for single-coordinated OH groups on the electronegativity of nonacid atoms for a great variety of oxides.

---

Pe OH- . , , OH- .

     

Cluster model for the surface OH groups of beryllium oxide

Cluster models calculated by a semiempirical CNDO method are used to describe properties of the surface hydroxy groups of beryllium oxide. The results are compared with those obtained from IR studeies and with data on BeO energy bands.

---

- , . , BeO.

     

The calculation of monocyclic molecular structures using MINDO/3

A comparison is made of the experimentally determined structures for some 4, 5, and 6 membered monocyclic rings and the MINDO/3 calculated structures. Among several systematic deficiencies the calculated ring structures are found to be too flat. This is attributed to the fact that MINDO/3 underestimates 1,4-eclipsing interactions.     

Dipole moment derivatives from MINDO/3 semi-empirical MO calculations

Dipole moment derivatives for CO, NO, CO₂, H₂O, HCN, BF₃, CH₄, C₂H₄, C₂H₆, CH₃F, F₂CO and H₂CO molecules have been evaluated using MINDO/3 MO calculations. The values are compared with those obtained by other semi-empirical MO methods.     

Molecular dipole polarizabilities based on MINDO/1 and MINDO/2 wavefunctions

Molecular dipole polarizability values are derived from a MINDO/1 — and MINDO/2 — “finite perturbation treatment”. The results are, especially in the MINDO/1 case, surprisingly good.     

Radical hydroxylation of aromatic hydrocarbons examined by MINDO/3 methods

MINDO/3 calculations have been made on the potential-energy surfaces for the attachment of OH^. radicals to benzene (1) and naphthalene (2) in the vapor state. The activation energies of these reactions are calculated as 88 and 58 kJ/mole. while the enthalpies at 298K are calculated as –211 and –199 kJ/mol. The transition states in (1) and (2) lie closer to the reagents than the products on the reaction coordinate, while (1) has an earlier transition state than does (2). The transition states in these reactions have high dipole moments: 3.1 and 3.6 D, respectively, which are due to charge transfer from the hydrocarbons to the OH^.. Quantum-chemical calculations and kinetic data on the reactions of aromatic hydrocarbons with OH^. in aqueous solution indicate that the mechanism is probably not one involving electron transfer and a rate-limiting stage in the attachment. These processes are of high performance because the radicals are of high stability, while polar effects determine the selectivity.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 20–26, January–February, 1986.     

Calculations of p-alkyltoluenes and their radicalcations by the MINDO/3 method

p-Cymene and p-cyclopropyltoluene and their radical-cations were calculated by the LCAO-MO SCF method in the MINDO/3 valence approximation. It was shown that the radical-cations are stabilized through , conjugation of the methyl groups.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 348–350, May–June, 1990.     

MINDO/SR calculations of nickel surface properties as a function of hydrogen coverage

The MINDO/SR method is used to study surface properties such as the work function, heat of adsorption and magnetic moment as a function of hydrogen coverage. A good correlation between theory and experiment is found. Furthermore, a qualitative analysis of surface geometry changes due to hydrogen chemisorption is presented.     

Template electrosynthesis of La(OH)3 and Nd(OH)3 nanowires using porous anodic alumina membranes

High quality arrays of Ln(OH)₃ (Ln = La, Nd) nanowires have been successfully fabricated for the first time by an electrochemical process using anodic alumina membrane templates. A physico-chemical characterisation of electrodeposited hydroxides has been carried out by different techniques (XRD, SEM and EDX). The results show that the synthesized nanostructures are crystalline, dense, continuous, well aligned, and with high aspect ratio, suggesting further development of possible applications in the lanthanide family species.     

A MINDO/3 study of the hetero-Diels–Alder reaction

The transition states involved in the hetero-Diels–Alder reactions of acrylaldehyde–ethylene and butadiene–formaldehyde systems were characterized using an efficient method of locating a saddle point on the energy surface of two coordinates calculated with MINDO /3 method. It has been shown that parallel transition and rotation of the conjugate coordinate frame lead to the reaction and orthogonal coordinate system on the hyperbolic paraboloid energy surface. It was concluded that the method we adopted is similar to the “X-method” but is much simpler to apply to real reaction systems.     

Determination of the surface hydroxy groups on alumina and silica-alumina catalysts by dimethylzinc

The earlier proposed pulse flow method for the determination of surface OH groups based on the reaction of gaseous dimethylzinc tetrahydrofuranate with active hydrogen was applied to alumina and silica-alumina catalysts. The concentrations of OH groups found by this method are in a good agreement with the published data, obtained by deuterium exchange and gravimetry.

---

, , OH, , - . OH, , , .