CONFORMATIONAL AND CONFIGURATIONAL STUDY OF 1,3-DIOXOLANES BY PROTON AND CARBON NMR-SPECTROSCOPY

The configurational and conformational properties of six 4-trimethylammoniummethyl 2,2-disubstituted 1,3-dioxolanes were studied using NOE experiments and vicinal coupling constants. Selective 1D NOE experiments proved to be effective tools in the configurational assignment of C-2 relative to C-4, The preferred conformation of the dioxolane ring and the exocyclic group at C-4 was obtained by employing vicinal coupling constants and NOE results. The H-1 and C-13 NMR chemical shifts show stereochemically dependent trends, Quantitative analysis of conformer populations was performed using Haasnoot et al's equation. The -N+(CH3)(3) group was found to be synclinal with respect to the heterocyclic 0-3 atom and points outside the ring, When a phenyl group is present at C-2, the 4-CH2N+ - group in a trans relationship to the 2-phenyl ring was found to occur prevalently in a pseudo-axial orientation, whereas it was established to be prevalently pseudo-equatorial when cis with respect to the phenyl ring.