Structure stereochemical effects

Through the years from his laboratory studies under Thorpe until his return to London in 1944, and still afterward, the heart of Ingold s theoretical chemistry was a recognition of the complementary roles in chemical processes of three-dimensional structure and physicochemical forces. His early career is marked by an effort to sort out the directing role in reacting molecules played by electrical and polar effects, in combination with stereochemical effects studied by chemists imbued with nineteenth-century concepts of structure and valence. 

Although mass spectrometry is a powerful and particularly sensitive tool in structural analysis, stereochemical aspects are more difficult to resolve by mass spectrometric means [ 1 ]. Of course, there do exist some time-honored examples for stereochemical effects showing up in mass spectra, and as a good example may serve the pronounced differences in the Retro-Diels-Alder (RDA) reactions of polycyclic compounds such as syn-1 and anti-l upon electron ionization (El) as shown in Scheme 1 [2]. 

R. B. Lessard, M. J. Heeg, T. Buranda, M. W. Perkovic, C. L. Schwarz, Y. Rudong, and J. F. Endicott, Inorg. Chem., 31, 3091 (1992). Stereochemical Alterations of E Chromium(lII) Excited-State Behavior in Dicyanotetraazacyclotetradecane Complexes. Ground State X-Ray Crystal Structures, Photophysical Behavior, and Molecular Mechanics Simulations of Stereochemical Effects. 

The reactant may be considered as a polarised carbonyl bond, reflected in contributions of covalent and ionic resonance structures. As the reaction proceeds, the contribution of both of these is replaced by the structure at the right of the diagram. Because of the greater concentration of positive charge on carbon in the reactant, donor substituents stabilise reactants more than transition state. In summary, donor substituents deactivate carbonyls. Cieplak acknowledged that the reactivity effect of a donor might be different from its stereochemical effect. 

Chemical reactions in the gas phase generally are often very sensitive to stereochemical effects, leading to the generation of very specific structural data. 

This chapter describes in detail the hierarchical self-assembly of lithium-bridged helicates that are in equilibrium with the corresponding monomeric building blocks in solution. Structural and thermodynamic principles of the reaction were investigated in solid, solution, and gas phases and are well understood. The scope and the limits of the process related to metal ion or ligand variations were also discussed. In addition, it was shown that the peripheries of the complexes can be decorated to obtain novel dendrimers or observe some unprecedented stereochemical effects. The work is now on a level to be utilized for the development of functional materials or in systems chemistry. 

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