RESUMO
In this article, we employed the induced magnetic field method to show that the Al2X6 (X = F, Cl, Br, I) clusters cannot be classified as aromatic systems. Interestingly, even nucleus independent chemical shift (NICS) reveals the same conclusion when analyzed in greater detail, showing that a superficial analysis of this index can easily lead to incorrect interpretations. In view of the fact that the NICS index is extensively used by computational and theoretically oriented experimental chemists, this is an important warning against superficial analyses, as it can lead to erroneous chemical interpretation.
RESUMO
The most stable forms of E(5)Li(7)(+) (E = Ge, Sn, and Pb) have been explored by means of a stochastic search of their potential-energy surfaces by using the gradient embedded genetic algorithm (GEGA). The preferred isomer of the Ge(5)Li(7)(+) ion is a slightly distorted analogue of the D(5h) three-dimensional seven-pointed starlike structure adopted by the lighter C(5)Li(7)(+) and Si(5)Li(7)(+) clusters. In contrast, the preferred structures for Sn(5)Li(7)(+) and Pb(5)Li(7)(+) are quite different. By starting from the starlike arrangement, corresponding lowest-energy structures are generated by migration of one of the E atoms out of the plane with the a corresponding rearrangement of the Li atoms. To understand these structural preferences, we propose a new energy decomposition analysis based on isomerizations (isomerization energy decomposition analysis (IEDA)), which enable us to extract energetic information from isomerization between structures, mainly from highly charged fragments.
RESUMO
Density functional theory calculations are used to predict structures and reactivity (barriers for sigmatropic shifts and retrocycloadditions) of 1,5-hexadienes fused to cubanes.