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A density functional theory (DFT) study is performedto determine the stability of the complexes formed between eitherthe N or O site of 3-methyl-4-pyrimidone and 1-methyl-2-pyrimidonemolecules and different ligands. The studied ligands are boron andalkali Lewis acids, namely, B(CH3)3, HB(CH3)2, H2B(CH3), BH3, H2BF, HBF2, BF3, Li+, Na+, and K+. The acids are divided into twogroups according to their hardness. The reactivity predictions, accordingto the molecular electrostatic potential (MEP) map and the naturalbond orbital (NBO) analysis, are in agreement with the calculatedrelative stabilities. Our findings reveal a strong regioselectivitywith borane and its derivatives preferring the nitrogen site in bothpyrimidone isomers, while a preference for oxygen is observed forthe alkali acids in the 3-methyl-4-pyrimidone molecule. The complexationof 1-methyl-2-pyrimidone with these hard alkali acids does not showany discrimination between the two sites due to the presence of acontinuous delocalized density region between the nitrogen and theoxygen atoms. The preference of boron Lewis acids toward the N siteis due to the stronger B–N bond as compared to the B–Obond. The influence of fluorine or methyl substitution on the boronatom is discussed through natural orbital analysis (NBO) concentratingon the overlap of the boron empty p-orbital with the F lone pairsand methyl hyperconjugation, respectively. The electrophilicity ofthe boron acids gives a good overall picture of the interaction capabilitieswith the Lewis base. [ABSTRACT FROM AUTHOR]

Density functional theory calculations at the B3LYP/SVP and B3LYP/6-31lG(d) levels were carried out for a series of XH3B80 complexes with X = {N, P, As, B, Al}. To probe the regioselectivity of B80, the electronic Fukui function, the molecular electrostatic potential (MEP), and the natural bond orbital (NBO) were determined. These indices were shown to provide reliable guides to predict the relative reactivities of the boron buckyball sites. Thermodynamic stabilities of the complexes formed by the reaction of B80 with nucleophiles (NH3, PH3, AsH3) and electrophiles (BH3, A1H3) are in good agreement with the prediction of regioselectivity indicated on the basis of Fukui and MEP indices. The qualitative results suggest the boron buckyball to be an amphoteric and hard molecule. It has two distinct reactive sites localized on caps and frame, which act as acids and bases, respectively. Most of the complexes are stable with formation energies comparable to that of the analogous complexes of the borane molecule, BH3BH3, BH3NH3, and BH3A1H3. The B-H-B bond characteristics of diborane are recovered in B80BH3. Exohedral complexes are more stable than endohedral complexes. The most stable complexes are those with NH3 on the caps and BH3 on the pentagonal ring of B80. [ABSTRACT FROM AUTHOR]