Weiss's endo- and exo-tetracyclo[5.5.1.0.^2,6 0^10,13]tridecane-4,8,12-trione: analysis of ¹H NMR couplings in a system of fused 5-membered rings

Abstract

. Can. J. Chem. 72,1926Chem. 72, (1994.The configurational isomers of the title compounds consist of four fused five-membered rings. They contain tightly coupled 'H NMR spin systems, which provide excellent models for establishing the relationships between coupling constants and conformation. Complete chemical shift assignments and spin-spin coupling constants are reported for the title compounds by using high-field (500 MHz) 'H NMR techniques (e.g., 2D homonuclear and heteronuclear experiments, difference NOE enhancements, and computational spin simulations). In addition to the more familiar two-and three-bond couplings, the spectra of 1 and 2 also contain a number of long-range (four-and five-bond) couplings, which provide a stringent test of Barfield's theoretical treatment of four-bond couplings.