Configurational activity

This chapter presents detailed and thorough studies of chemical synthesis in three quite different chemical systems zinc ferrite, intermetallic, and metal oxide. In addition to different reaction types (oxide-oxide, metal-metal, and metal oxide), the systems have quite different heats of reaction. The oxide-oxide system has no heat of reaction, while the intermetallic has a significant, but modest, heat of reaction. The metal oxide system has a very large heat of reaction. The various observations appear to be consistent with the proposed conceptual models involving configuration, activation, mixing, and heating required to describe the mechanisms of shock-induced solid state chemistry. 

Comparison of the configuration of the stannane with the prodncts of reaction reveals that primary alkyl halides that are not benzyhc or a to a carbonyl react with inversion at the lithium-bearing carbon atom. In the piperidine series, the best data are for the 3-phenylpropyl compound, which was shown to be >99 1 er. In the pyrrolidine series, the er of the analogous compound indicates 21-22% retention and 78-79% inversion of configuration. Activated alkyl halides such as benzyl bromide and teri-butyl bromoacetate afford racemic adducts. In both the pyrrolidine and piperidine series, most carbonyl electrophiles (i.e. carbon dioxide, dimethyl carbonate, methyl chloroformate, pivaloyl chloride, cyclohexanone, acetone and benzaldehyde) react with virtually complete retention of configuration at the lithium-bearing carbon atom. The only exceptions are benzophenone, which affords racemic adduct, and pivaloyl chloride, which shows some inversion. The inversion observed with pivaloyl chloride may be due to partial racemization of the ketone product during work-up. 

Use the Electron Configuration activity in eChapter 5.12 to determine the subshell being filled as you move across a period in each of the following groups of elements ... 

After completing the Ion Electron Configuration activity (eChapter 6.1) answer the following questions ... 

Source of the Pfeiffer Effect. No completely satisfactory explanation has yet been set forth which accounts for all of the observations associated with the Pfeiffer effect. Dwyer and co-workers (7) have proposed a configurational activity explanation which states that the dextro and levo enantiomers of optically active, labile complexes in solution are in equilibrium (with Keq. = 1), but that in the presence of an optically active environment the equilibrium shifts in favor of one of the enantiomers, resulting in a change in optical rotation. However, this proposal does not account for the fact that the effect is observed for some labile complexes and not for others. 

The double bond has the Z configuration. (Activity is reduced but not eliminated if the double bond is E.)... 

It was, and still is, possible to assign the whole of the configurational activity to the influence of diastereoisomers in solution, and therefore to assign it to interionic contacts, but it now appeared in conditions where ion pairs were not of dominant importance in accounting for other aspects of solution behaviour (Sections... 

No special equilibrium between activated complexes and reactants is assumed. It is supposed however, that within the space between qi and qi+Aqi, q2 and q2+Aq2, configurations (activated complexes) have impulses (motions) between pi and pi+Api,p2 and P2+AP2 respectively. These configurations are computed in accordance with Maxwell-Boltzmann distribution. Recall from the gas laws that an energy profile for molecules can be describe by the Maxwell-Boltzman distribution diagram (Figure 3.3). As the temperature goes up, the population of molecules with more energy also increases. 

Coevolution of Manufacturing Systems, Fig. 3 IDEFO model for the configuration activity... 

Using chiral molecules, Dwyer discovered a phenomenon to which he gave the name configurational activity". Briefly, this means that the activity coefficients of optical isomers are different in an asymmetric environment provided by another optically active ion(7,34) He predicted that configurational activity should be of biological importance, since the rates of many enzyme processes should be changed by the addition of inert optically active complex ions(3 ). This work provided a better theoretical framewoik for the Pfeiffer effect and subsequently influenced the theory of chiral interactions. 

Configurational activity and equilibrium shift postulates are also supported in an experimental sequence reported by Dwyer and his co-workers. A solution of [Ni(phen)3] when placed with such active species as /-quinine, BCS or even the resolved complex d-[Co(en)3] and treated with iodide ion permits a fractional precipitation of the nickel complex. It is reported that the least soluble fraction is dextro rotatory (about 0.1° as a saturated solution) and the more soluble fraction, levo. On standing this fraction becomes more levo. The separated fraction now, on fractional precipitation with iodide, showed that the least soluble fraction had no rotation and the most soluble fraction was levo rotatory. These observations according to Dwyer would be consistent with a d-/ complex equilibrium shift and would not necessitate interaction between the complex and the resolved species. 

Data derived by Dwyer on the ratio of the rate constants (kjki) has been criticized by Harris since the values used by Dwyer for the rotation at the end of the racemization of d-[Ni(phen)3] were those obtained immediately after adding the optically active ion to the racemic mixture of the complex in solution. The ratio thus was not the equilibrium rotation. It was not reasonable, according to Harris, to use the data in support of an equilibrium theory for the Pfeiffer effect. Contradictory results are reported by Craddock and Jones in that no difference was found for the racemization rates for either isomer (e.g., d- or /-[Ni(phen)3] ) if the complex is in the presence of an optically active species. These authors point out that another environmental factor, temperature, could have accounted for unusual or anomalous rotations previously found. It is evident that something more than an equilibrium shift or a configurational activity is needed to explain Pfeiffer rotations. 

The configurational activity concept is not in keeping with the time-rotation study of the present authors as well as Pfeiffer s own studies on the system [Ni(phen)3](BCS)2. Since the racemization rate of the nickel(II) complex is slow, any shift in the equilibrium of the d- and /-isomers of the complex should also be slow. The Pfeiffer effect for this complex would be expected to increase from a zero value to a maximum. The observed data shows an instantaneous increase (vide supra) that is about 46% of the final rotation. Although from this study an equilibrium shift may be operative it cannot be the only effect. 

The Pfeiffer effect is not adequately explained by the concept of an equilibrium shift or configurational activity. There is strong evidence for interaction between the resolvable complex and the optically active species by a bonding force that is proposed herein to be hydrophobic in character. Ion pair interaction (when oppositely charged species exist), equilibrium shift, differential association and the hydrophobic bonding are suggested as contributing to the Pfeiffer activity. 

It is in many other aspects different from all the catalyst systems t discussed in previous sections. It is based on a half-sandwich metallocene molecule that cmitains an amido-type N-Ti bond and is a 12-electron system (14-electron system at the most if one considers the contribution of the nitrogen s lone pair of electrons to the overall N-Ti bonding) leaving a cationic 10-electron (maximum 12 including the lone pair electrons of N) electron configuration active site. ... 

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