Solvent-induced 1H NMR chemical shifts of annulenes

Abstract

We computationally investigate the effect of solvent polarity on the 1H NMR chemical shifts of a few annulenes using multiple DFT levels within the IEFPCM solvation formalism. The solvent polarity is parametrized by defining a dielectric function that can efficiently quantify the solvent-induced shift (SIS). Both the linear and the nonlinear SIS behavior are observed. As the polarity of the solvent increases, the value of SIS decreases for both the inner and the outer protons of [12]- and [30]annulenes as well as for the outer protons of [18]annulene. For the inner protons of C2 [18]annulene, the nonlinearity is primarily due to the anisotropic environment inside the annulenic ring cavity, i.e. due to the existence of an anisotropic reaction field. Interestingly, the SIS values computed using multiple DFT levels within the IEFPCM solvation directly fit into the relatively simple Onsager’s reaction field model.