SURVEY OF POSSIBLE STRUCTURES NOMENCLATURE

Abstract This chapter is devoted to recent progress in the chemistry of the 5 5 fused heterocyclic systems. There are four possible modes of 5 5 fusions of the simple five-membered heterocycles leading to four structures containing one heteroatom in each ring. The heteroatoms may be the same or different and may be O, NH, S, Se, Te, P, As, or Sb. The fully conjugated hetero analogs of pentalene dianion have a central C-C bond and are isoelectronic with the 10-7t-electron pentalene dianion. The scope of the chapter is outlined with a survey of various structural types and nomenclature of the parent compounds and their derivatives. New synthetic procedures and synthetic applications of title compounds are presented. This review has concentrated on the new developments achieved from 1997 to September 2007. 

Theory and experimental methods. Since the combined experimental-theoretical approach is stressed, both the underlying theoretical and experimental aspects receive considerable attention in chapters 2 and 3. Computational methods are presented in order to introduce the nomenclature, discuss the input into the models, and the other approximations used. Thereafter, a brief survey of possible surface science experimental techniques is provided, with a critical view towards the application of these techniques to studies of conjugated polymer surfaces and interfaces. Next, some of the relevant details of the most common, and singly most useful, measurement employed in the studies of polymer surfaces and interfaces, photoelectron spectroscopy, are pointed out, to provide the reader with a familiarity of certain concepts used in data interpretation in the Examples chapter (chapter 7). Finally, the use of the output of the computational modelling in interpreting experimental electronic and chemical structural data, the combined experimental-theoretical approach, is illustrated. 

If appropriate, this commences with a brief historical piece, and comments on the relationship of the new chapter to the corresponding chapter in CHEC, and also gives general references to reviews of the material. The scope of the chapter is outlined with a survey of the various structural types and nomenclature of the parent, its non-conjugated isomers, partially reduced compounds, oxo compounds and benzo derivatives. Distinction is made here between the structural types possible and those which are known and treated in the chapter. 

A question that will always require careful consideration, however, is whether introduction of a new trivial name is justified. Besides, replacing certain trivial names by more or less systematic ones can result in greatly improved surveyability of various highly specialized parts of organic chemistry and thus facilitate their further development. An example is the excellent report on the nomenclature of steroids published a short time ago in various languages (I) as a result of a conference of specialists in this field with the aid of a limited number of conventions, it appeared possible to replace the cumbersome trivial names of many compounds of well-known structure by systematic names of very reasonable length and form from which the structure can clearly and easily be deduced. 

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