This Review is a brief account of our theoretical contributions in seven research communications in the field of reaction mechanisms. Some mechanisms were corrected as in the case of the Baeyer-Drewsen indigo synthesis. When two very different reaction mechanisms had been proposed, as in the Clemmensen Reduction, a unified theory was provided. In other cases there were no reaction mechanisms at all, as in the Baeyer-Emmerling synthesis of indigo and in the Froehde Reaction for opioids. This deficit has been solved. The reaction that controls fructosazone regiochemistry has been described, and an internal process in a mixed osazone formation has been explained. All the proposals are based on well known reactivities and we provide complete and coherent reaction series with commented steps.

In the 1 H NMR spectra of several thiazole derivatives we have found that some of them present downfield shifts (to higher frequency). These ∆∂ can be attributed, in a broad sense, to intramolecular hydrogen bonding. However, we present an AIM study that shows there are two types of atomic interactions in these compounds: some originate bond critical points, but others do not. It is interesting to note that intramolecular hydrogen bonds were formed when a six-member ring and an electronegative atom, such as oxygen or chlorine, were involved. However, interactions involving five-member rings and a nitrogen atom as electron donor showed only three of the six required theoretical properties for hydrogen bonding. These special interactions can be considered as very weak hydrogen bonds. Nevertheless, both types of atomic interactions caused similar downfield shifts in the 1 H NMR spectra. Thus, this study reveals differences in the nature of the atomic interactions that gave rise to downfield shifts in the 1 H NMR spectra.

3,4-Dimethoxybenzoylacetonitrile, required in the synthesis of some isoxazole derivatives, was obtained from α-bromoacetoveratrone and potassium cyanide. In this reaction, a byproduct could be isolated. From its IR, 1 H-NMR, MS and elemental analysis data, it was identified as 2,3-bis-(3,4-dimethoxybenzoyl)propionitrile. A careful study of its NMR spectrum revealed the existence of two intramolecular weak hydrogen bonds, in solution in CDCl 3 , of the type C-H---O=C. Paramagnetic shifts, Δδ, of 0.5 and 1 ppm, were found for the hydrogens involved in the interactions, as well as significant differences in the coupling constants. A molecular model confirmed the findings made by the conformational analysis. Thus, the secondary structure of the title compound was established.

Das durch Kondensation von D‐Xylose mit Diaminodimethyluracil gebildete Xylosylideniminodimethyluracil (I) ergibt mit Acetanhydrid und Perchlorsäure das Tetraacetat (II); bei höherer Temperatur entsteht die Verbindung (III).