Reactivity central atom concepts

The chemist is much concerned with the relationship between the structure and reactivity of substances. A knowledge of such a relationship enables the chemist to make new compounds which have certain desired properties. The Brdnsted acid-base reaction is a common and relatively simple reaction we therefore use it to discuss the relationship of structure and reactivity. We here restrict our discussion to the oxyacids and oxyanions. We will first present the facts about reactivity, and then we will present a broad concept to rationalize the relative reactivities. The acidity of oxyacids follows periodic patterns and is also influenced by the oxidation number of the central atom. 

Elementary reactions on solid surfaces are central to heterogeneous catalysis (Chapter 8) and gas-solid reactions (Chapter 9). This class of elementary reactions is the most complex and least understood of all those considered here. The simple quantitative theories of reaction rates on surfaces, which begin with the work of Langmuir in the 1920s, use the concept of sites, which are atomic groupings on the surface involved in bonding to other atoms or molecules. These theories treat the sites as if they are stationary gas-phase species which participate in reactive collisions in a similar manner to gas-phase reactants. 

An application of the synthetic concept to carbon analogs is not possible. LiSPh-elimination and/or LiSPh-elimination after previous H,Li exchange occurred for alkyllithium-intermediates formed by reductive cleavage of C-S bonds. Reaction of this type have been observed for similar compounds [7]. The silicon atom obviously plays a central role in the reactivity of the presented structure types. 

Centropolyindanes constitute a complete family of arylaliphatic polycyclic hydrocarbons containing several indane units. Mutual fusion of the five-membered rings leads to three-dimensional, carbon-rich molecular frameworks bearing a central carbon atom, such as benzo-annelated [3.3.3]propellanes, triquinacenes, and [5.5.5.6]- and [5.5.5.5]fenestranes. In this review, the structural concept of centropolyindanes is contrasted to other fused indane hydrocarbons. Besides the syntheses of the parent centropolyindanes and recently described related indane hydrocarbons, the preparation of a large variety of bridgehead and arene substituted centropolyindanes is presented including strained, heterocyclic, and centrohexacyclic derivatives. In appropriate cases, the particular reactivity and some structural features of these unusual, sterically rigid polycyclic compounds are pointed out. 

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