Computer-aided prediction of 125Te and 13C NMR chemical shifts of diorgano tellurides

Abstract

Esse trabalho descreve um método para previsão dos deslocamentos químicos de RMN de 125 Te e 13 C de diorgano-teluretos baseado em uma abordagem tridimensional. Para tanto, 150 substâncias foram selecionadas da literatura e tiveram suas respectivas geometrias otimizadas através do método semi-empírico PM3. A partir desses dados, as estruturas foram codificadas através do programa FOCOS, que descreve o ambiente químico de cada átomo presente na estrutura, num total de 1411 focos para as substâncias. O método descrito foi testado com dez diorgano teluretos não inseridos na base de dados e mostrou uma exatidão maior na previsão de deslocamentos químicos de RMN de 125 Te e 13 C do que os dados previstos por um programa comercial. Os dados e os parâmetros estatísticos obtidos nesse estudo demonstram que o método aplicado foi capaz de prever com sucesso os deslocamentos químicos de RMN de 125 Te e 13 C dos diorgano teluretos.This work describes a method to predict the 125 Te and 13 C NMR chemical shifts of diorgano tellurides based in a three-dimensional approach. For that, a collection of 150 compounds were selected from the literature and had their geometry optimized using the PM3 semi-empirical method. From this data, the structures were coded by the FOCOS program which described the chemical environment for each atom present in the structure, totalizing 1411 focos for the substances. The method developed was tested with ten diorgano tellurides not inserted in the database showing a higher accuracy in the prediction of 125 Te and 13 C NMR chemical shifts than those predicted by the commercial program. The chemical shifts and the statistical parameters obtained in this work demonstrate that the method applied was able to predict successfully the 13 C and 125 Te NMR chemical shifts of the diorgano tellurides.

Prediction of chemical shift in NMR: A review

“…For 19 F shifts, Saunders et al [61] achieved a maximum deviation of 6.5 ppm for fluorinated (hetero)aromatic compounds. Vulpetti et al [62] report a root mean squared error (RMSE) of 1.08 for a CF3 test set and 2.37 for a CF test set, but does not offer a prediction for all cases. Emerenciano et al [63] predict 125 Te and 13 C shifts for diorgano tellurides. A MAE of 0.67 is reported for 13 C , which is a very good result, but only applies to a specialized class of compounds.…”

New Improvements in Automatic Structure Elucidation Using the LSD (Logic for Structure Determination) and the SISTEMAT Expert Systems

“…A new prediction program based on a 3D codification scheme is briefly described below. It was developed recently [25,26] based on a set of 1000 steroidal molecules from the SISTEMAT database. The molecules were subjected to geometry optimization by means of a semi-empirical quantum mechanical calculations method, namely AM1 (Austin Model 1) [27,28] with the root mean square (RMS) gradient value of 0.001 kcal/mol as the termination condition.…”