Structural Theory of Organic Chemistry

In 1866 only a few years after publishing his ideas concerning what we now rec ognize as the structural theory of organic chemistry August Kekule applied it to the structure of benzene He based his reasoning on three premises... 

The convenience and usefulness of the concept of resonance in the discussion of chemical problems are so great as to make the disadvantage of the element of arbitrariness of little significance. Also, it must not be forgotten that the element of arbitrariness occurs in essentially the same way in the simple structure theory of organic chemistry as in the theory of resonance — there is the same use of idealized, hypothetical structural elements. In the resonance discussion of the benzene molecule the two Kekule structures have to be described as hypothetical it is not possible to synthesize molecules with one or the other of the two Kekule structures. In the same way, however, the concept of the carbon-carbon single bond is an idealization. The benzene molecule has its own structure, which cannot be exactly composed of structural elements from other molecules. The propane molecule also has its own structure, which cannot be composed of structural elements from other molecules — it is not possible to isolate a portion of the propane molecule, involving parts of two carbon atoms... 

To conclude this section, we can state that all of the theories presented hitherto, even when starting from general principles, inevitably embody several assumptions, which in fact represent the heart of the analysis. However, the physical meaning of these assumptions usually is not known, so that no theory is able to predict in which reaction series isokinetic behavior appears and in which it does not. Neither is the structural theory of organic chemistry able to make such a prediction and to define the terms reaction series or similar reactions or small structure changes it can only afford many examples. 

N. D. Epiotis, W. R. Cherry, and S. Shaik, in "Structural Theory of Organic Chemistry, pp. 1-250. Springer-Verlag, Berlin, 1977. 

In the second half of the nineteenth century the structural theory of organic chemistry was developed. It led to the concept that chemical, physical and biological properties of all kinds must vary with structural change. The earliest structure-property relationships (SPR) were qualitative. With the development of methods of quantitative measurement of these properties data accumulated. Attempts were then made to develop quantitative models of the structural dependence of these properties. These methods for the quantitative description of structural effects will now be described. 

Epiotis, N.D., Cherry, W.R., Shaik, S., Yates, Y.L. and Bernardi, F. (1977). Structural Theory of Organic Chemistry. Part III, p. 131, Springer-Verlag, Berlin... 

Epiotis, N. D. et al. Structural theory of organic chemistry. Berlin, Heidelberg, New York Springer 1977... 

It is remarkable that, in the space of less than two decades, the structural theory of organic chemistry should have moved from the first hesitant steps, where the chemical structure was considered to be separate and distinct from the physical structure of the molecule, and represented only the "affinities" of the atoms within the molecule, to the point where those same formulas were now viewed as representations of the actual physical locations of the atoms in the molecule (76). What was left undone at the end of the nineteenth century, by which time three-dimerrsional graphical formitlas for organic compoimds were in routine use, was, of coruse, a description of exactly what the "chemical affinities" of the atoms composing the molecules were. The answer to this problem would have to await the new century, and the development of modem theories of the atom and bonding. 

Moreover, it must not be forgotten that the element of arbitrariness occurs in essentially the same way in the simple structure theory of organic chemistry as in the theory of resonance there is the same use... 

The essential identity in character of the theory of resonance and the classical structure theory of organic chemistry, which has before been referred to only briefly,42 will be discussed in detail in the following paragraphs. 

Theoretical chemistry rates some special mention in this context. Nowadays this activity tends to be quite mathematical [1], but history shows us that theoretical chemistry need not be mathematical at all. From the first years of the crystallization of chemistry as a subject distinct from alchemy, chemists have utilized theory, in the sense of disciplined speculation. Nonmathematical examples are found in the structural theory of organic chemistry [2] and in most applications of the powerful Woodward-Hoffman orbital symmetry rules [3]. 

N. Epiotis. Structural Theory of Organic Chemistry, Springer, NY, 1977. 

The discovery of stereochemistry was one of the most important breakthroughs in the structural theory of organic chemistry. Stereochemistry explained why several types of isomers exist, and it forced scientists to propose the tetrahedral carbon atom. In this... 

In O.T. Bentfey Journal of Chemical Education August Kekule and the Birth of The Structural Theory of Organic Chemistry in 1858 (p. 21) Volume 35, Number 1, January 1958... 

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