Solvent induced 1H NMR chemical shifts of annulenes

Abstract

We investigate the effect of solvent polarity on the 1H NMR chemical shifts of [n]annulenes (n = 12, 18, and 30) using density functional theory and corroborate the computational results with Onsager’s reaction field theory. We observe that there is a complete deshielding of the proton NMR chemical shifts for the outer protons and these shifts depend linearly on the dielectric function of the solvents reaction field for certain annulenes (n = 12 and 30). For the asymmetric C2 structure of [18]annulene, the inner protons are observed to vary nonlinearly with the function of solvent dielectrics due to the influence of the asymmetry parameter “C”, which generates an anisotropic environment inside the annulene ring cavity.