Conformations of disaccharides by empirical, force-field calculations: Part III, β-gentiobiose

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The conformational flexibility of β-gentiobiose has been studied by using convergent energy minimisation in a new force-field, with relaxation of all degrees of freedom. Twenty-four local minima are found in the φ,ψ,ω-space. The free-enthalpy differences are 1.7, 3.7, 5.1, 5.3, and from 5.9 to 29.4 kJ.mol −1 above the lowest minimum, corresponding to a distribution of 40:20:9:5:5:21 at 298 K. Each minimum is surrounded by a manifold of minimum conformers that differ only in exocyclic torsions. The average conformation of β-gentiobiose is not fully extended, but to some degree coiled. Three conformers are shown in stereo.