Periodic orbits synthesis

The period 1930-1980s may be the golden age for the growth of qualitative theories and conceptual models. As is well known, the frontier molecular orbital theory [1-3], Woodward-Hoffmann rules [4, 5], and the resonance theory [6] have equipped chemists well for rationalizing and predicting pericyclic reaction mechanisms or molecular properties with fundamental concepts such as orbital symmetry and hybridization. Remarkable advances in aeative synthesis and fine characterization during recent years appeal for new conceptual models. 

Concepts of valence and the construction of the periodic table have always been associated with one another. As the idea of electronic distribution in orbitals developed, the role of the noble gases and the concept of filled shells were stressed in many theoretical developments. It must be emphasized that most theoreticians never thought in terms of an absolute prohibition of reactions for the noble gases. Indeed, for awhile the possibilities of compoimd formation for xenon and even for krypton were suggested. It was only after a number of claims for the synthesis of compounds were discredited and the best investigations of such... 

Boron.— The remarkable structural behaviour of boron, which tends to confound the newcomer, continues to receive considerable attention, although the extent of the coverage of boron compounds is perhaps reduced by the difficulties of synthesis which often exist. Since it is immediately to the left of carbon in the periodic table and only sli tly less electronegative, covalent behaviour predominates, but the electron-deficiency of simple tervalent-boron compounds leads to an extensive variety of molecules in which boron acquires electrons in various ways, particularly from nearby bonds or lone pairs. Interpretation of the structures observed frequently involves molecular-orbital calculations, which emphasize the multicentred bonding so often found. 

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