Ground-state compression effect

In the intramolecular reactions studied by Bruice and Koshland and their co-workers, proximity effects (reduction in kinetic order and elimination of unfavourable ground state conformations) and orientation effects might give rate accelerations of 10 -10 . Hence, these effects can by themselves account for the enhancements seen in most intramolecular reactions. However, a factor of 10 -10 is less than the rate acceleration calculated for many enzyme reactions and certain intramolecular reactions, for example, hydrolysis of benzalde-hyde disalicyl acetal (3 X 10 ) (Anderson and Fife, 1973) and the lactonization reaction of[l] (10 ) where a trimethyl lock has been built into the system. If hydrolysis of tetramethylsuccinanilic acid (Higuchi et al., 1966) represents a steric compression effect (10 rate acceleration), then proximity, orientation, and steric compression... 

The modeling of the effective magnetic moment is shown in Fig. 15. It can be seen that for a compressed bipyramid (v = AaxA < 0) the effective magnetic moment nearly follows the octahedral pattern. Since the ground state r6 is nonmagnetic in the z-direction (which results from the calculated Zee-man coefficients Zz(r6) = 0 and Zz(r7) = 1.82), the z-component of the susceptibility should change to zero when the temperatureis lowered. In the x-direction, however, a small Zeeman coefficient appears (Zx(/),) = 0.05 and ZX(17) = 0.26) so that the x-componenl of the susceptibility rises when the temperature is lowered (Fig. 16). 

Table 8.6. Effect of a compressive stress on the ground state of deep centres with site symmetries C3v or D3d, with an orientational degeneracy of 4 [14]...

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