Configuration, retained

Inhibition of configuration-retaining glycosidases by lactones, piperidines, and tetrazoles 99AG(E)750. 

T. D. Heightman, A T. Vasella, Recent Insights into Inhibition, Structure, and Mechanism of Configuration-Retaining Glycosidases , Angew. Chem. Int. Ed. 1999, 38,750-770. 

A significant variational improvement can be obtained if orbital and spincoupling coefficients are simultaneously relaxed in a corresponding MCSC calculation, using six configurations constrained to be related by C3 and ov as above. Six orbitals of each configuration spontaneously remain pure-c. The last two orbitals of each configuration retain the (o ln) nature they had in the three-... 

When the non-rigid molecule in a random configuration retains some symmetry, the restricted NRG is expected to be smaller than the full NRG. 

Heightman, T D, Vasella, A T, Recent insights into inhibition, stmcture, and mechanism of configuration-retaining glycosidases, Angew. Chem., Int. Ed., 38, 750-770, 1999. 

However with a ligand which is not capable of producing such a pronounced splitting, such as the ammonia molecule, we obtain a complex with five unpaired electrons, i.e. with the expectedlerric ion configuration retained. 

Contrary to the rotationally symmetric bridgehead substitution (azoalkanes 5a,b,c), which leads to the unselective triplet reaction channel and selective formation of anti-configured (retained) housanes (Scheme 7), the direct photolysis of the rotationally unsymmetric bridgehead-substituted azoalkanes 5d,e is moderately diastereoselective for both the singlet and triplet modes of photolysis (Scheme 9), as evidenced by the synjanti (inversion/retention) ratio. Thus, the photolysis of 5d,e affords under singlet conditions (high-temperature direct photolysis) predominantly the retained housanes anti-14d,e syn anti 21 79 for housane 14d and 33 67 for 14e) while under triplet conditions (low-temperature direct or benzophenone-sensitized photolysis), the inverted diastereomer syn-14d,e is favored syn anti 61 39 for 14d and 70 30 14e). 

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