The Structural Theory of Organic Chemistry

How many valence electrons does each of the following atoms have  

Between 1858 and 1861, August Kekule, Archibald Scott Couper, and Alexander M. Butlerov, working independently, laid the basis for one of the most important theories in chemistry the structural theory. 

The atoms in organic compounds can form a fixed number of bonds using their outermost shell (valence) electrons. Carbon is tetravalent that is, carbon atoms have four valence electrons and can form four bonds. Oxygen is divalent, and hydrogen and 

A carbon atom can use one or more of its valence electrons to form bonds to other carbon atoms  

Single bond Double bond Triple bond 

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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... 

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. 

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. 

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. 

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]. 

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... 

In the 18th century, a number of naturally occurring compounds were isolated and described as "aromatic" because of their distinctive odor.1 When the structural theory of organic chemistry was developed in the 19th century, it became apparent that most of these compounds were benzene derivatives. As a result, they became known as aromatic compounds, in contrast to aliphatic compounds. 

Isolated examples of isomeric organic compounds were known as early as the 1830s. This phenomenon turned to be a touchstone for the structural theory of organic chemistry formulated in the 1850s owing to the efforts of Kekule, Cooper, and Butlerov. It was Butlerov who not only advanced the consistent explanation of isomerism in terms of this theory but also predicted the existence of all theoretically possible isomers for a number of simple C4 and C5 derivatives (1864). Subsequent synthesis of these isomers served as a convincing proof of the validity of the structural theory. 

It looked for a while as if there were two quite independent valence patterns, one for the compounds of carbon and the other for the rest of chemistry. Werner, however, insisted that the structural theory of organic chemistry was a special case of coordination theory, the carbon atom having a valence equal to its coordination, number. The two theories did not find a common footing imtil the advent of electronic valence theories. 

In my freshman course, I dealt with the ideal gas laws and the kinetic molecular theory that accounted for them. My organic chemistry classes explored the structural theory of organic chemistry developed in 1858byKekuleandCouper. Ineachofthose fields, I had to point out that the initial simple theory had to be amplified. Gases in fact were not ideal real gases did not exactly obey the simple laws of Boyle, Charles, and Gay-Lussac and the beautifully simple structural theory of 1858 could not account for all cases of isomerism. 

We divided the six concepts into three pairs, the first dealing with space, the second with time, and the third with the classic discrete/continuous dichotomy, already evident in the distinction between arithmetic and geometry. Placing the members of each pair of concepts on opposing faces of the cube in Figure 1, each face is in contact with each of the others except for the face directly opposite. Adjacent faces of the cube represent phenomena which require both concepts, can be explained by either concept, or lead to a new conceptual development subsuming both as in the space-time continuum of relativity theory. The concept of velocity requires both direction in space (3D) and duration in time (t). As seen in the previous section, certain failures encountered in the structural theory of organic chemistry can be explained either in spatial terms... 

Spatial relations among organisms are central to ecological studies and to the concept of territoriality. The chemical counterpart is the study of chemical interactions, stereochemistry (The Structural Theory of Organic Chemistry, and valence forces... 

This relation indicated that a group of elements could play the part of an atom. The first attempt made to solve the mystery of complex organic compounds was directed toward the discovery of the radicals which they contained. This was the beginning of the structure theory of organic chemistry. 

A test of the limits of the structural theory of organic chemistry, ever since Baeyer introduced the concept of angle strain [11], chemists have wondered how much distortion of bond angles can be packed into a molecule. Cyclopropane is the simplest example of a strained organic molecule and tetrahedrane is composed of four fused cyclopropane rings. Can such a molecule exist If so, how stable would it be ... 

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 chapter, we study the three-dimensional structures of molecules to understand their stereochemical relationships. We compare the various types of stereoisomers and study ways to differentiate among stereoisomers. In future chapters, we will see how stereochemistry plays a major role in the properties and reactions of organic compounds. 

The development of the chemistry of organic lead compounds can be divided into three stages. Following the preparation of the first alkyllead compound, hexaethyldiplumbane, in 1853 by Lowig 171), attention was focused on the concept of valence and also the development of the structural theory of organic chemistry, mainly in view of early theories of radicals. Then in 1929 Paneth and collaborators 214, 215), in their classical experiment with tetramethyllead and tetraethyllead, were able to prove beyond doubt the existence of short-lived free radicals, long before anything was known of electron spin resonance spectroscopy. 

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