Um estudo de DFT em derivados 5-NI foi realizado em diferentes níveis de teoria, a fim procurar a melhor metodologia para calcular constantes de acoplamento hiperfinas (hfccs), distribuições da densidade da rotação e propriedades eletrônicas, sabendo-se que é difícil obter boa concordância entre os valores de hfccs calculados e experimentais para compostos radicais centrados no nitrogênio. Os híbridos funcionais diferentes B1LYP, B3LYP e PBE0 foram usados conjuntamente com vários meios para aumentar o tamanho da base estudada. O modelo de C-PCM foi considerado para interações do soluto-solvente. As comparações de nossos cálculos com os dados experimentais precedentes obtidos por meio de medidas de EPR e raios-X confirmaram que esta aproximação computacional representa importante avanço. Nossos resultados indicaram que os efeitos solventes e a consideração de funções difusas são os fatores mais importantes no cálculo de constantes hiperfinas de acoplamento para este sistema nitro-heterocíclico. Foi verificado também que algumas propriedades eletrônicas calculadas como orbital de LUMO, funções condensadas de Fukui para ataques nucleofílico e afinidade de elétron não são correlacionadas como esperado com a atividade biológica.

A DFT study on 5-NI derivatives was carried out at different levels of theory, in order to seek for the best methodology that helps us to calculate hyperfine coupling constants (hfccs), spin density distributions and electronic properties, since it is difficult to obtain a good agreement between calculated and experimental hfccs for nitrogen center radical compounds. Different functional hybrids namely B1LYP, B3LYP and PBE0 were used in conjunction with various medium to large size basis sets. C-PCM model was considered for solute-solvent interactions. Comparisons of our calculations with previous experimental data obtained from EPR and X-ray techniques confirmed that this computational approach represents an important aid. Our results indicated that solvent effects and consideration of diffuse functions are the most important factors on the calculation of hyperfine coupling constants for this nitro-heterocyclic system. Also, we found that some electronic properties calculated (LUMO orbital, condensed Fukui functions for nucleophilic attacks and electron affinity) do not correlate as expected with the biological activity.

Condensation of 4-methylthiobenzaldehyde with 1-nitropropane unexpectedly afforded separable amounts of both (E)- and (Z)-1-(4-methylthiophenyl)-2-nitrobutene. The ¹H and 13C NMR spectra allowed the unequivocal assignment of all signals and their correlation with the preferred conformations adopted by these compounds as determined by NOESY experiments. Hartree Fock theory optimizations at the 6-311G(d,p) level were carried out for the stereoisomeric 4-methylthionitroethene, -nitropropene, and -nitrobutene pairs, and the relative energy differences between isomers were calculated in order to estimate approximate E/Z equilibrium constants. These energy differences decrease with the increasing number of side chain carbon atoms, explaining the possibility of separating (E)- and (Z)-nitrobutenes and the failure to isolate the (Z) isomers of the lower homologues under the usual thermodynamically controlled reaction conditions

The conformational preferences of a series of 1-benzyl-1,2,3,4-tetrahydroisoquinolines (norlaudanosine and coclaurine analogues) were investigated with the aid of their 1H NMR spectra and NOESY experiments, coupled with ab initio theoretical studies to estimate energy barriers among the various stable conformers of these systems. The secondary amines prefer an extended conformation, while the N-alkylated derivatives prefer a semi-folded one, with considerable freedom to exchange between both forms. A third, folded conformation, although not much higher in energy, is relatively inaccessible