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ABSTRACT:High level ab initio calculations at the B3LYP/6-311ϩϩG(d,p) and MP2(full)/6-311ϩϩG(d,p) levels employing PCM/UA0 model with different van der Waals' radii for the systems that contain lithium atoms have been carried out, in order to see if the van der Waal's radius for lithium atom employed in the default PCM/UA0 model is proper or not. Comparative analysis indicated that the van der Waals' radius for alkali metals, especially for lithium atom in the default PCM/UA0 model within the Gaussian 03 package, is too small, which causes erroneous redundant imaginary frequencies (RIFs) in the characterization of Li-containing compounds from moderate to big size. A new set of van der Waals' atomic radii based on QTAIM, proposed by Bader, was suggested for a better choice in the characterization of compounds containing alkali metals, for which it can effectively avoid the erroneous RIFs for corresponding geometries of these Li-containing systems.

Density functional theory (DFT) and second order Møller-Plesset perturbation (MP2) calculations, employing the 6-311++G(d,p) basis set, were carried out on alkyl-substituted aziridines to explore the reaction mechanisms and regioselectivity associated with their ring-opening conversions to oxazolidinones, in the presence of carbon dioxide. Computational results, employing the self-consistent reaction field polarizable continuum model (SCRF(PCM/Bader)), indicated that the conversions proceed with thermodynamic ease in THF solvent at room temperature. It is proposed that the N-alkylaziridine promotes ring opening through a SN2 attack of the iodide ion, of catalytic lithium iodide, on the preformed complex. The oxazolidinone regioisomer ratio is highly sensitive to aziridine ring-carbon substitution. Therein, monophenyl substitutions show preference to opening more highly substituted carbon-nitrogen bonds, providing rationale as to why experimental works result in an exclusive oxazolidinone regioisomer product.

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