π-Electron transfer as calculated at various levels of basis set. A redefinition of the theoretical scale of σR° values

Abstract

Ab initio molecular orbital calculations are reported for the π-electron transfer to or from the substituent for 20 monosubstituted benzenes, both at the minimal STO-3G basis set and at the split-valence 4-31 G basis set. Evidence from i.r. intensities, experimental σ_R° values, rotational barriers, dipole moments, the protonation of cyanides XCN, and stabilisation energies all indicate that it is the STO-3G basis that better reproduces the experimental data for systems where π-electron transfer is important. The theoretical σ_R° scale is redefined using π-electron transfers for monosubstituted ethylenes at the STO-3G//STO-3G basis.