CNDO/2 method reactions

In refs. 2-1.128) jjj terms of the CNDO method, the coordination of ethylene on a monometallic AC with various alkyl groups has been analyzed CHj (complex A, reaction (24)), trans-C- Hj (complex C, reaction (25, 26)), and cw-CjHj (complex F, reaction (27)- 29)). In all cases, the initial and final states of the AC in the process of ethylene coordination are optimized by the minimum of the overall energy. This process includes the construction of potential surfaces in two independent coordinates, according to the change of the position of alkyl and ethylene. Several possibilities of ethylene entering into the coordination sphere of Ti(III) ion have been calculated. 

Alkylation. Theoretical treatment by the CNDO method, and the analysis of orbital interactions, show a frontier orbital control for the S -methylation of MeNHC(S)NHMe. Kinetic measurements of the alkylation of thioureas with alkyl halides or tosylates have shown that this reaction is first-order in thiourea and alkylating agent, implying an 5 n2 mechanism, with direct attack by the sulphur atom. 

During this, the electrons of the partial X—Z multiple bond are used. Experiments show that the ester can be further active in the polymerization. Its reactivity, however, is reduced in comparison with ion pairs. From a mechanistical point of view, the chain propagation should proceed in the manner of a SN2 reaction, that is with the monomer as nucleophile and the ester as substrate. With the assistance of quantum chemical calculations using the CNDO/2 method, the differences between covalent species and free ions should be examined. The following contains the three types of anions used ... 

Figures 5 and 6 give the 77- and total electronic charges calculated by the CNDO/2 method for several tautomeric forms of cytosine, 5-F and 6-F-cytosine, and of N8-amino and N8-hydroxy substituted cytosines. The last two compounds as discussed before are important in the theory of mutagenesis, being products of reaction between cytosine and hydrazine or hydroxylamine, respectively.

In particularly thorough examples of the traditional physical organic approach, Parker (1969) and Abraham (1974) interpreted solvent effects on Walden inversion reactions by using thermodynamic transfer functions. However, in order to explain the reaction rate decrease upon solvation from a microscopic point of view, quantum mechanical electronic structure calculations must be carried out. Micro-solvated Sn-2 reactions were initially studied in this way, with the CNDO/2 semiempirical molecular orbital (MO) method, by using the supermolecule... 

The results of the refined MO calculations (tt-SCF MO without and with Cl, open-shell tt-SCF MO, tt-UHF, or CNDO/2 Cl methods) differ depending on the approximations used. In some cases, the tt-SCF MO Cl method gives results quite similar for both states to those obtained by tt-HMO method for the first excited state. These results [spin densities, bond orders Pge, and free valences on the C(5)-C(6) bond] all correlate with the greater tendency to photodimerization of uracil and thymine compared with cytosine and do not indicate which of the excited states is involved in the reaction. On the other hand, Danilov et using the tt-SCF MO CI as well as the open-shell tt-SCF... 

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