The Study of HOMO Energy for Showing the Basicity and the n(C=O) Stretching Bands Obtained by the Semi-empirical and ab initio Methods in Phosphorus Ylides

Shun-ichi MITOMOa*, Sumio TOKITAa and Manabu SENOb

aDepartment of Applied Chemistry, Faculty of Engineering, Saitama University
255 Shimo-Ohkubo, Sakura-ku, Saitana, Saitama, 338-8570, Japan
bCollege of Science and Technology, Nihon University
1-18-14 Kanda-surugadai, Chiyoda-ku, Tokyo 101-0062, Japan

(Received: October 5, 2004; Accepted for publication: March 15, 2005; Published on Web: June 10, 2005)

Relationships between the HOMO energy, the n(C=O) stretching band, basicity(pKa), and s(p) in phosphorus ylides have been studied. A linear relationship between the HOMO energies obtained by the AM1, HF/3-21G, and HF/6-31G methods and pKa was found. The same linear relationship was found between the HOMO energies obtained by these methods and s(p)(indicated p-position). Thus, the HOMO energy can be adopted instead of pKa and s(p) for choosing the ylide as the donor in organic reactions. In addition, a linear relationship between the n (C=O) stretching bands obtained by these methods and the parameters described above was found.
Hence, as for the electron donation of the ylide, it is noted that the HOMO energy can be used instead of pKa as a new method for showing the basicity of ylides. Furthermore, the n(C=O) stretching bands obtained by these methods can be estimated by the HOMO energy obtained by the same methods.

Keywords: Ylides, HOMO energy, pKa, n(C=O) stretching bands, Semi-empirical method, ab initio method

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