Conformational analysis of cis‐3, 5‐dioxa‐bicyclo[5.4.0]undecane and its 4‐substituted derivatives by DNMR, molecular modeling, and GIAO/DFT methods

Abstract

Temperature-dependent (1)H and (13)C-NMR spectra of the title compounds are presented. Coalescence effects are discussed and assigned to dynamic process--the interconversion of bicyclic system. The free energies of activation covered the range 39-52 kJ/mol. The dioxepane ring adopts twist-chair (TC) conformation. GIAO/DFT calculation of isotropic shieldings for the set of low-energy conformations showed that only one conformer is present at 298 K in solution that matched well with experimental data.