AMI methods

Semi-empirical methods are sometimes suggested for studying isodesmic reactions. We performed this same study using the AMI method the results are given in the following table ... 

Tautomeric interconversions of 1,3-diimino-isoindolenine and its nitro and amino derivatives have been studied theoretically by the AMI method (97MI9). 

Arguing that the MNDO method is more suitable than the AMI method for predicting the heats of formation of five-membered nitrogenated aromatic rings, Garcia and Vilarrasa (88H1803) calculated that 4-fluoroimidazole 14a (R = F, = H) is 2.5 kJ mol more stable than its tautomer 14b,... 

Bond orders and charge densities of 4//-pyrido[l, 2-u]pyrimidin-4-one and its protonated form were calculated by the semiempirical AMI method with full optimization of geometry (97MI22). 

Bond orders, charges on the atoms in 1 l//-pyrido[2,l-Z)]quinazolin-l 1-one and its protonated form were calculated by quantum chemical calculations by the semiempirical AMI method. According to the results, the equilibrium conformation of the ring in 1 l//-pyrido[2,l-Z)]quinazolin-l 1-one is planar, while l//-pyrimido[l,2-u]quinolin-1-one adopts a conformation close to a half-chair due to the unfavorable interactions between the oxygen atom of the carbonyl group and the ring C-10 atom in the pen-position (97MI22). 

Two models of practical interest using quantum chemical parameters were developed by Clark et al. [26, 27]. Both studies were based on 1085 molecules and 36 descriptors calculated with the AMI method following structure optimization and electron density calculation. An initial set of descriptors was selected with a multiple linear regression model and further optimized by trial-and-error variation. The second study calculated a standard error of 0.56 for 1085 compounds and it also estimated the reliability of neural network prediction by analysis of the standard deviation error for an ensemble of 11 networks trained on different randomly selected subsets of the initial training set [27]. 

The conformation with the lowest found energy from the previous conformational analysis was subjected to a geometry optimization (energy minimization) using the semi-empirical quantum chemistry-based AMI method available in the Spartan program. 

Using the semiempirical AMI method with full structure optimization, the bond lengths and bond angles of 4- and 5-aminoimidazoles (179) and (180) have been calculated [92JCS(P 1)2779] and the results are summarized in Table X. 

Experimental dipole moments and acidities of azoles, including 1,2,3-triazole, show linear correlations with their Jt-electron excess calculated by the semiempirical AMI method <2003CHE71>. Experimental dipole moments of azoles agree well with those calculated by the DFT program ALLCHEM <2003PCA4172>. Calculated dipole moments t (in units of Debye,D) of a few selected azoles are listed below ... 

AMI semi-empirical and B3LYP/6-31G(d)/AMl density functional theory (DFT) computational studies were performed with the purpose of determining which variously substituted 1,3,4-oxadiazoles would participate in Diels-Alder reactions as dienes and under what conditions. Also, bond orders for 1,3,4-oxadiazole and its 2,5-diacetyl, 2,5-dimethyl, 2,5-di(trifluoromethyl), and 2,5-di(methoxycarbonyl) derivatives were calculated <1998JMT153>. The AMI method was also used to evaluate the electronic properties of 2,5-bis[5-(4,5,6,7-tetrahydrobenzo[A thien-2-yl)thien-2-yl]-l,3,4-oxadiazole 8. The experimentally determined redox potentials were compared with the calculated highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) energies. The performance of the available parameters from AMI was verified with other semi-empirical calculations (PM3, MNDO) as well as by ab initio methods <1998CEJ2211>. 

More recent calculations using the AMI method were applied in order to distinguish between two possible structures 9 and 10, affording a more stable conformation of each isomer <2003T4591>. 

Jakdetchai and Nakajima/Wang and coworkers—theoretical models favor redox mechanism. Beginning in 2002, a number of theoretical models were published in Theochem studying the water-gas shift reaction over Cu(110), Cu(lll), and Cu(100) surfaces. Perhaps the first was by Jakdetchai and Nakajima,325 relying on the AMI method. The main goal of the study was (1) to determine whether or not theoretical calculations are consistent with a redox or associative (e.g., formate) mechanism and (2) whether the kinetics are described best by a Langmuir-Hinshel-wood expression or an Eley-Rideal expression. That is, in the case of a redox model, does the adsorbed O adatom react with adsorbed CO or directly with gas phase CO Their approximate A//a[Pg.205]

Theoretical calculations were carried out for the rationalization of the ring closure reactions yielding thiazolo[2,3-7][l,2,4]triazinones 47 <2003PS1143>. PM3 and AMI methods were applied which revealed that the observed regioselective cyclization is in accordance of the charge control of the reaction. 

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