Aromatic Solvent-induced Shift(ASIS). I. An Interpretation Based on the Dipole-Quadrupole Interaction

Abstract

Abstract Two general theoretical ways of estimating aromatic solvent-induced shifts(ASIS), which are based on the dipole (solute)-induced diple (solvent) interaction [(μ-μ′) interaction] or the dipole (solute)-quadrupole (solvent) interaction [(μ-Q) interaction], are proposed. Solvent shifts can occur by means of the magnetic anisotropy of solvent molecules, which take specific orientations due to those electro-static interactions. As an example, we calculate the ASIS of a hypothetical spherical molecule, a model for camphor, with a dipole near the center and covered with protons, immersed in benzene. The estimated ASIS based on (μ-μ′) interaction is much too small to account for the shifts normally observed, while those based on (μ-Q) interaction agree well with the observed ASIS in respect to both its magnitude and angular dependency (e.g., the carbonyl plane rule). More specifically, the theoretical and experimental ASIS for methyl protons of camphor are compared.