Stereo-dynamic effects

The tethered catalyst 24a proved to be superior over its untethered version 26 in the reduction of functionalised acetylenic ketones 27 with FA-TEA as hydrogen donor (Fig. 8) [59]. High enantioselectivity and substituent tolerance of these ketones indicate that the alkyne group has a dominating stereo-controlling effect through C-Wn interaction. Additionally, an efficient dynamic kinetic resolution was observed with substrates 27 favouring the syn products. The table in Fig. 8 shows selected examples of the reduction of acetylenic p-keto esters. 

Cimino P et al (2010) Interplay of stereo-electronic, rarvironmental, and dynamical effects in determining the EPR parameters of aromatic spin-probes INDCO as a test case. Phys Chem... 

Shorter chain analogs of DPPC were also investigated in order to determine if the lack of stereo-differentiation in monolayer properties could be due to DPPC s higher gel point or complicating steric effects. Figure 15 shows the compression/expansion isotherms of DPPC as compared with racemic and enantiomeric dimyristoylphosphatidyl choline (DMPC) and dilauroyl phosphatidyl choline (DLPC). Again no stereodifferentiation in monolayer properties was observed as reflected by 11/A isotherms or dynamic surface tension. 

The first driver for the adoption of modelling software was the ability to provide helpful visualisations even now, a graphics workstation with a stereo display is a must-see for any open day. The appreeiation of the numerieal power of modelling calculations came later, as force fields improved. There is still the issue of the most effective way to represent a moleeule a reeeptor sees a dynamic cloud of electrons, but often we need to represent the same... 

Summary The collection of examples and concepts provided in this chapter illustrates that timing of stereo-electronic interaction determines their effects on reactivity. Delocalizing interactions can be counterproductive when they fade out of existence along the reaction path or productive/accelerating when they are amplified in the transition state. In the following sections, we will provide further examples of dynamic stereoelectronic interplay between structure and reactivity in a variety of chemical areas. 

In this contribution we intend to provide a eomprehensive review on PLA stereo-complex, including preparation, strueture-properties and biomedical applications. The effect of stereo-complex on the thermal dynamics, hydrolytic degradation, micellization and hydrogelation will be discussed. 

The multivalence structure of chemical elements opens numerous possibilities for chemical product formation, energy utilization and distribution, stereo-selectivity and product orientation. Experiments on the effect of selective product formation and vibrational, translational and orientational excitation of reactants in bimolecular reactions can give important insight into their microscopic dynamics. The information obtained in such experiments can be compared with the results of theoretical calculations of the reaction dynamics based on ab initio potential energy surfaces and is also of fundamental interest for improving the kinetic data used in detailed chemical kinetic modelling. 

Brancato G, Rega N, Barone V (2007) Unraveling the role of stereo-electronic, dynamical, and environmental effects in tuning the structure and magnetic properties of glycine radical in aqueous solution at different pH values. J Am Chem Soc 129 15380-15390... 

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