Solvent-induced 1H NMR chemical shifts of annulenes

• Published in: Computational and theoretical chemistry Vol. 1236; p. 114601
• Main Authors: Goyary, Swrangsi, Sarmah, Manash Jyoti, Goswami, Himangshu Prabal, Nath, Nilamoni
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2024
• Subjects: Annulene; Onsager Reaction Field Theory; Solvent-induced shifts; Solvent-induced shifts; Annulene; Onsager Reaction Field Theory
• ISSN: 2210-271X
• DOI: 10.1016/j.comptc.2024.114601

[Display omitted] •Understanding the linear and nonlinear SIS (solvent-induced shift) behaviour for [n]annulenes (n: 12, 18, and 30) as a function of solvent polarity.•The outer protons of all the [n]annulenes are deshielded to a lesser extent than the inner protons.•A direct fit is obtained between the simple Onsager reaction field formalism and the results computed using multiple DFT levels within the IEFPCM solvation.•Different degrees of nonlinear SIS behaviour are observed in the same [n]annulene.•[18]annulene is found to possess an anisotropic reaction field inside its ring cavity, which leads to a higher degree of nonlinearity in the SIS values of the inner protons. 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.