Changes of Electron Donation by Substituents for SN Ylides Obtained by ab initio Calculations

Relationships between the HOMO energy and σ(p) in ylides 1-14 have been studied. Linear relationships between the HOMO energies obtained by HF/3-21G[*] and 6-31G*, BLYP/6-31G*, and B3LYP/6-31G* methods and the substituent constant (σ(p)) were found, respectively. Hence, for the electron donation of the ylide, it is noted that the HOMO energy can be used as a new parameter for predicting the basicity of SN ylides. By comparing the results obtained by these calculations, the best method is found to be B3LYP/6-31G*. The results of bond lengths and torsion angles obtained by DFT calculations correspond with that of X-ray structure determinations.