An Electron‐Density‐Based Study on the Ionic Reactivity of 1,3‐Azoles

Abstract

Basic processes for the ionic chemistry of 1,3‐azoles (protonation, nitration, hydride addition, and deprotonation) have been studied by analyzing B3LYP/6‐311++G(2d,2p) 6d electron densities using the Quantum Theory of Atoms in Molecules (QTAIM) and delocalization indices in the gas phase and in aqueous solution modeled with the Polarizable Continuum Model (PCM) method. The most stable protonation site is N3 in all cases, and this takes place without a significant change in electron delocalization, whereas C5 is the preferred site for electrophilic substitution. Activating and deactivating effects on the carbon atoms of the imidazole ring were tested by analyzing the variation of atomic properties introduced by amino and nitro substituents, respectively. The largest activation was observed for C5 in 4‐aminoimidazole. C2 is the most favored site for hydridation in all 1,3‐azoles, which always results in loss of ring planarity and reduced electron delocalization in the ring. PCM calculations allow the experimentally observed preferred deprotonation C‐site in water for these compounds to be modeled and reproduced. In all anions, QTAIM charges do not keep in line with the resonance forms; whereas QTAIM describes deprotonated carbon atoms as positive or nearly neutral in the gas phase, they should display negative charge according to the resonance model.

Computational Study on the Conformational Preferences of Neutral, Protonated and Deprotonated Glycine Dimers

“…Diverse studies previously carried out in a series of simple hydrogen bond complexes, as well as conformational analysis [34][35][36], concluded that relative energies could be explained on the basis of the summation of atomic electronic populations of hydrogens. This is not the case, as could expect taking into account the disparity of IHBs (and other factors) here involved.…”

Electron Density Analysis on the Alpha Acidity of Nitriles

“…Even, different possibilities to supply resonance structures with more reliable and quantitative weighting coefficients obtained making use of modern tools of electron density topological analysis can be explored [5]. Nevertheless, since the publication of the seminal paper by Wiberg and Laidig on the electronic origin of the esther and amide resonance [6], it is not possible to deny that a large amount of inconsistencies between RM predictions and computed evolutions of electron densities have been reported [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Most of these discrepancies where obtained studying protonation processes or in nucleophilic addition reactions.…”

Synthesis, Characterization and Thermal Stability Study of New Heterocyclic Compounds Containing 1,2,3-Triazole and 1,3,4-Thiadiazole Rings

“…Azoles ring system containing heterocyclic compounds have a special importance due to a wide range of different applications 4,5 . Azole is a five-membered ring containing nitrogen atom and at least one other non-carbon atom of either nitrogen, sulphur, or oxygen [6][7][8] . Among many different azole structures, 1,4-disubstituted-1,2,3-triazole and 2-amino-1,3,4-thiadiazole derivatives (Fig.…”