Cyclic oxonium salts: ¹³C magnetic resonance spectroscopy. The correlation of chemical shifts with the calculated charge density

Abstract

Abstract The 13 C chemical shifts of several bicyclic and monocyclic oxonium salts are reported and, in the case of 5‐membered ring unsaturated oxonium salts, compared with ab initio and CNDO calculated charges. A prime dependence of the 13 C shielding on the π charge delocalization effects induced by the Y group is established for the Y‐substituted C‐α carbon; a good correlation of δC‐α vs q π is obtained, using π bond‐order terms. However, contradictory information arises from NMR and theoretical calculations for the C‐ω carbon, which is distant from the Y group. The results are discussed.