MNDO calculation

Obtain the dipole moment of methylenecyclopropene by a MNDO calculation and compare your answer with the result obtained from Hnckel molecular orbital calculations. 

Fig. 10. Most stable ground-state geometries found for CjjjLia and C Li,4 by the MNDO calculations the Li atoms are represented by the filled black circles.

A preliminary study of the above equilibrium, using 4-31G//MNDO calculations and including thermal and solvation energies [82JPR(324)827], was significantly improved by subsequent calculations. Enchev increased the level of the calculations to 4-31G//STO-3G and considered four other... 

Sporadic reports of the 2//-thiopyran transformation are still available. The electrocyclic ring-opening of 2-benzyl-2,4,6-triphenyl-2//-thiopyran (131, X = PhCH2) was detected by laser flash spectroscopy (86MI1). 2-Amino-2//-thiopyran was predicted to be more stable than its valence-bond isomer on the basis of semiempirical MINDO/3 and MNDO calculations (84JPR955). 

Analogous MNDO calculations for nonaromatic 1-aryl- and l-acyl-2-pyrazo-line-3-diazonium ions (8.24) were made by Glukhovtsev et al. (1990). 

See related MNDO calculations by Butler s group (Anderson et al., 1989) and the study of electrophilic aromatic substitutions by Jorgensen s group (Bures et al., 1985, Table 2 and references cited in that table). 

Pyman and Timmis investigated azo coupling reactions of imidazoles as long ago as 1922. Ridd and coworkers suggested in another relatively early publication (Brown et al., 1953) that reaction of imidazole occurs not via the neutral molecule but via the anion, despite the fact that imidazole is a very weak acid (pK = 14.5). Butler s group (Anderson et al., 1989) confirmed this suggestion by kinetic experiments in the pH range 6.52-7.48, supported by informative MNDO calculations. 

SCHEME 1. Energy levels (eV) of the HOMO and LUMO obtained from MNDO calculations of some sulfones and sulfonyl-like compounds. 

The authors would like to thank Mr. Rajzmann for performing theoretical MNDO calculations and M. Meyer for her help in the preparation of the manuscript. Drs Petrillo and Marino read the manuscript at the proof stage and we thank them for useful suggestions and comments. 

As can be seen from Table I, the C-C bond distance as described by LDF is closer to experiment than the corresponding HF value obtained with a 6-3IG basis. Including correlation via second and third order Moller-Plesset perturbation theory and via Cl leads to very close agreement with experiment. The C-H bond length is significantly overestimated in the LDF calculations by almost 2%. The HCH bond angle is reasonably well described and lies close to all the HF and post-HF calculations. Still, all the theoretical values are too small by more than one degree compared with experiment the deviation from experiment is particularly pronounced for the semi-empirical MNDO calculation. 

However, this kind of compounds has not been extensively studied theoretically [12,15], At the semi-empirical level, we point out the MNDO calculations of Williams [12] concerning chains of less than 14 carbon atoms, and the fNDO computations of Kirtman [15[ related to polymeric chains containing up to carbons. To our knowledge no ab-initio evaluation of... 

The corresponding syn-P-hydroxy-a-methyl aldehydes do not react through a chelated TS,112 which appears to be due to steric factors that raise the bicyclic TS by several kcal relative to the anti isomers. The monocyclic six-membered TS does not incorporate these factors and the syn isomer reacts through a monocyclic TS. Figure 9.3 depicts the competing TSs and their relative energies as determined by MNDO calculations. 

Modified neglect of diatomic overlap (MNDO) calculations can support the structures assigned to certain of these fused tricyclic systems, such as 401, where confirmatory X-ray crystallographic data are lacking <1983JCM128>. 

The geometries of silabenzene and four of its isomers were optimized using ab initio calculations at the STO-3G level (isomers 3-5 and 1)(60,193) or using semi-empirical MNDO calculations (isomer 6)(194). 

The parent heterocycle of pyrido[2,3-e][l,2,4]triazine and its phenyl derivative 39 were prepared (89JHC475) by cyclization with polyphos-phoric acid of 3-acyIhydrazino-2-aminopyridines 36, obtained by reduction of the corresponding 3-acylhydrazino-2-nitropyridines 35. Compounds 35 were obtained from 3-fluoro-2-nitropyridine 34 either by reaction with benzoylhydrazine or by reaction with hydrazine and subsequent for-mylation of the initially formed 3-hydrazino-2-nitropyridine 38. Attempts to prepare 38 from 3-chloro-2-nitropyridine gave 2-hydrazino-3-chloropyridine 37. These results could be explained by semiempirical calculations (CNDO and MNDO calculations). 

Hexacyano[3]radialene (50) is a very powerful electron acceptor according to both experiment23,24 35 and MNDO calculations of LUMO energy and adiabatic electron affinity25. The easy reduction to the stable species 50" and 502- by KBr and Nal, respectively, has already been mentioned. Similarly, the hexaester 51 is reduced to 512-by Lil24. Most [3]radialenes with two or three quinoid substituents are reduced in two subsequent, well-separated, reversible one-electron steps. As an exception, an apparent two-electron reduction occurs for 4620. The reduction potentials of some [3]radialenes of this type, as determined by cyclic voltammetry, are collected in Table 1. Due to the occurrence of the first reduction step at relatively high potential, all these radialenes... 

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