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Ideas of Quantum Chemistry P46

Ideas of Quantum Chemistry P46 shows how quantum mechanics is applied to chemistry to give it a theoretical foundation. The structure of the book (a TREE-form) emphasizes the logical relationships between various topics, facts and methods. It shows the reader which parts of the text are needed for understanding specific aspects of the subject matter. Interspersed throughout the text are short biographies of key scientists and their contributions to the development of the field. | 416 8. Electronic Motion in the Mean Field Atoms and Molecules Fig. 8.29. How does the hybridization concept help The figure shows the all important proteins example of the peptide bond. a We assume a certain pattern of the chemical bonds this choice is knowledge based ignoring other possibilities such as the isomers shown in b . Apart from the methyl groups they have the familiar tetrahedral configuration the molecule is planar. Usually in chemistry knowing the geometry we make a conjecture pertaining to the hybridization of particular atoms. This leads to the electron count for each atom the electrons left are supposed to participate in bonds with other atoms. In the example shown the sp2 hybridization is assumed for the central carbon and for the nitrogen and oxygen atoms c . A n bonding interaction of the nitrogen carbon and oxygen should therefore stabilize the planarity of the system which is indeed an experimental fact. is one electron left. This is very good because it will participate in the OC n bond. Let us go to the partner carbon atom. It is supposed to make a double bond with the oxygen. Hence it is reasonable to ascribe to it an ethylene-like hybridization as well. Out of four valence electrons for carbon two are already used up by the a and n CO bonds. Two other sp2 hybrids remain that of course accommodate the two electrons and therefore are able to make two a bonds one with -CH3 and one with the nitrogen atom. Then we go to the nitrogen atom. It has three substituents in most cases in the almost planar configuration we know this from experiment . To make the analysis simple we assume an sp2 ideal hybridization. The nitrogen atom has five valence electrons. Three of them will go to form the a NC NH N-CH3 bonds. Note that although the configuration at N is assumed to be planar this plane may not coincide with the analogous plane on the carbon atom. Finally 8.10 A minimal model of a molecule 417 we predict the last two valence electrons of the .