Cremer-Pople ring pucker parameters

Cremer-Pople Puckering. Pyranose ring geometry is formally described by the Cremer-Pople puckering parameters Q, 0, and < )... 

The five-inembered ring has the E3 conformation, with a tendency towards the 3T2 form the Cremer-Pople puckering parameters89,70 are q= 42.0 pm and 4>2 = 102.98°, and the asymmetry parameters after Duax and coworkers91 are AC, = 8.4° for the E3 conformation and AC2 = 12.9° for the 3T2 conformation. The acetoxyl group on C-2 and the methyl group on C-4 are linked quasi-equatorially, whereas the AcO-3... 

Table 8-1. S, energy and Cremer-Pople parameters for the ring puckering conical intersections in aminopyrimidine, pyridone and pyrrole. Energies relative to the S0 energy in the ground state equilibrium geometry. The values in parenthesis are the CP parameters for the equivalent MXSs in 9H-adenine using the geometries given in [5]...

In accordance with the characteristics of conformer B, the thiazine ring in 92a assumes a skew-boat shape shifted somewhat toward the twist-boat form, whereas in 92b it has an almost perfect skew-boat conformation. The Cremer-Pople puckering parameters (< > = 89-%° and 0 = 69-77°) and the asymmetry factors for these conformations indicate a less (92a) and a more (92b) perfect symmetry axis bisecting the C-4—S-5 bond. Thus, the cw-fused triazoline ring with its N-2—C-3 double bond has an envelope conformation in 92a with the C-10 on the flap, but a halfchair conformation in 92b with a twofold axis bisecting C-3. Together,... 

Fig. 4.14. a, b Principal component plots derived for six-membered ring torsional datasets 6-C (1) and 6-C (2) respectively, c, d Plots of Cremer-Pople puckering parameters for six-membered ring datasets 6-C (1), 6-C (2) respectively... 

In this case, and indeed for all ring systems, the chemical meaning of the PC s now becomes obvious. The spherical conformational space of Figure 4.13 is related directly to the three Cremer-Pople puckering parameters 2>02> 3 [3]-... 

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