Similarity in Chemistry

There is probably no other concept that contributed to the development of chemistry so remarkably as the ill-defined, qualitative concept of similarity. Not despite but rather because of a certain fuzziness, the applicability of this concept is extremely broad and touches practically all areas of chemistry [1, 2]. An example would be the Mendeleev periodic law, the disclosure of which was closely connected with the effort to systematise the similarities in the properties of elements. From the intuitively interpreted meaning of similarity arises also one of the most powerful chemical principles - the principle of analogy, on the basis of which a wealth of fundamental chemical notions were introduced. 

The increasing use of similarity ideas in recent years was enriched by a new and interesting attempt to extend the applicability of the approach beyond the scope of static structure-activity relationships to what is the heart of chemistry -chemical reactivity. 

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Rouvray, D.H. Similarity in Chemistry Past, Present andFuture. 173, 1-30 (1995). 

Roth, H.D. Structure and Reactivity of Organic Radical Cations. 163, 131-245 (1992). Rouvray, D.H. Similarity in Chemistry Past, Present and Future. 173, 1-30 (1995). 

Similarity between quantum systems, such as atoms and molecules, plays a very important role throughout chemistry. Probably the best example is the ubiquitously known periodic system of the elements. In this system, elements are arranged both horizontally and vertically in such a way that in both directions, elements have a high similarity to their neighbors. Another closely related idea is that of transferability. In chemistry, one speaks of transferability of an entity when its properties remain similar between different situations. An example is the transferability of the properties of a functional group between one molecule and another. The main motto of using similarity in chemistry is the assumption that similar molecules have similar properties. 

Greisen Wolfiamite Tungsten-bearing hydrodiermal fluid stays with the intrusive. Intruded rocks are similar in chemistry to the intrusive rocks. Granite-like rock made up of quartz, mica, topaz, tourmaline, fluorite, cassiterite, wolfiamite. Typical association of W, Sn, and F. 

Similarity in chemistry refers to the analogy of molecnles in a structnral aspect, characteristics, or properties (see also Diversity). 

Introduction to similarity in chemistry, in Concepts and Applications of Molecular Similarity (eds M.A. Johnson and G. M. Maggiora,), Wiley-VCH Verlag GmbH, Weinheim, Germany, pp. 1-13. 

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