Three and four-ring systems

Table 5.1-5 Three and four-ring systems, cont. ...

Carbonaceous chondrites generally include many kinds of organics, which may have been abiotically synthesized and may record the early thermal histoiy of the solar system. Predominant organic materials detected in carbonaceous chondrites are aromatic polymers—two-, three-, and four-ring PAHs such as naphthalene, phenanthrene, pyrene, and chrysene [149]. Moreover, carbonaceous chondrites include volatile aromatic hydrocarbons such as benzene [42]. 

Glass-forming systems other than siUca have been examined. The fraction of three- and four-coordinated boron in borate glasses can be determined by nmr (29). Both nmr and x-ray diffraction (30) results led to the suggestion that the boroxyl ring is the stmctural unit of vitreous The... 

There are no exceptions in Tables 1 and 2 [7], For 4N electron systems, the singlet ground states of trimers and tetramers do not assnme three- and four-membered ring structures of and symmetry, respectively. 

Hudlicky T, Reed JW (1991) Rearrangements of vinyl cyclopropane and related systems. In Trost BM (ed) Comprehensive organic synthesis, vol 5. Pergamon Press, Oxford, p 899 Hudlicky T, Becker DA, Fan RL, Kozhushkov S (1997) Carbocyclic three-and four-member-ed ring compounds. In de Meijere A (ed) Houben-Weyl methods of organic chemistry, vol El7c. Thieme, Stuttgart, p 2538... 

In addition, five heterodiphospholes (T-X) are known and are also dealt with in this chapter. Within the scope of this chapter are five-membered rings with three and four phosphorus atoms but no other heteroatoms. In these systems, full cyclic conjugation can only be attained if all phosphorus atoms are two-coordinate. The ring consequently must be negatively charged as in the 1,2,4- and 1,2,3-triphospholides (Y, Z) and in the tetraphospholides (iE). The pentaphospholide (0) is again beyond the definition but must not be excluded here. 

Three- and Four-Membered Ring Systems Three-Membered Ring Systems... 

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