Chemical bonding, basic concepts compounds

Aromaticity has been long recognized as one of the most useful theoretical concepts in organic chemistry. It is essential in understanding the reactivity, structure and many physico-chemical characteristics of heterocyclic compounds. Aromaticity can be defined as a measure of the basic state of cyclic conjugated TT-electron systems, which is manifested in increased thermodynamic stability, planar geometry with non-localized cyclic bonds, and the ability to sustain an induced ring current. In contrast to aromatic compounds there exist nonaromatic and antiaromatic systems. Thus, pyrazine (69)... 

Open problems in writing the basic organic chonistry textbook include the selection of concepts for the representation of the material, but also the level of the explanation of the complex phenomena such as reaction mechanisms or the electron structure. Here I propose the compromises. First compromise is related to the mode of the systematization of the contents, which can traditionally be based either on the classes of compounds, or on the classes of reactions. Here, the main chapter titles contain the reaction types, but the subtitles involve the compound classes. The electronic effects as well as the nature of the chemical bond is described by using the quasi-classical approach starting with the wave nature of the electron, and building the molecular orbitals from the linear combination of the atomic orbitals on the principle of the qualitative MO model. Hybridization is avoided because all the phenomena on this level can be simply explained by non-hybridized molecular orbitals. 

Some of the basic concepts of organic chemistiy and how the principles of chemical bonding contribute to the understanding of organic compounds and reactions. 

On the basis of correlation analysis by LFER between the chemical structure and spectral data from IR and NMR, Lewis basicity, rate constant of hydrolysis as well as pKa of various organophos-phorus compounds, it is not likely that the benzene ring is conjugated with the phosphoryl group, and that the oxygen of the latter is linked to the phosphorus by a double bond, if the general concepts of conjugation in the chemistry of carbon compounds work as well in the phosphorus series. 

Structural formulas serve a key role as devices to facilitate communication of chemical information, but it is important to recognize at the outset that the relationship of a structural formula to molecular structure is a symbolic one. The current system of structural formulas arose largely as a result of chemistry done in the last half of the nineteenth century. Elemental analyses, interrelation of various compounds, and systematic investigation of the reactivity of various functional groups permitted organic chemists to deduce correctly much information about molecular structure. For many molecules, it became possible to draw conclusions as to which atoms were directly connected. Lines drawn between atoms were used to represent direct connections or bonds. These structural deductions predated modern concepts of atomic and molecular structure and of the nature of the forces that bind atoms. With the advent of quantum mechanics and new experimental techniques for accurate determination of such basic structural parameters as bond lengths and bond... 

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