Convergence for the /3-CI model conformer was obtained by constructing, at each cycle, not an extrapolated density matrix, but one representing 0.7 of the previous density matrix and 0.3 of the current density matrix. This is equivalent to applying a damping factor to the change in each array element of 0.3. ( 21) This anomeric energy may be an overestimate for the glycosyl chlorides, since it assumes that the CH3-0-CH2-CI torsion angle is unrestricted and 825 can have the optimum value of 74°. In a pyranose ring, this angle is constrained by the ring closure to be closer to 60°; In the two a glycosyl chlorides for which experimental data are available (see Table III), the C(5)-0(5)-C(1)-CI torsion angles are 68 and 72°.(22) These values represent energy differences between the actual minima and are a refinement of those reported previously (ref 14 and 15), where the standard torsion angles of 60 and 180°g ave energy differences of 3.0 and 2.4 kcal/mol for CH3-0-CH2-0H and CH3-0~CH2-0CH3, respectively.

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