Fundamental ring

Before turning to the dihydro and tetrahydro derivatives of the fundamental ring systems, we deal with two special classes. The pyrrolenines and the thiophene sulfones both contain two double bonds in the heterocyclic ring, but in each case the conjugation does not include all the ring atoms. Finally we consider hydroxy derivatives, most of which exist predominantly as the non-aromatic carbonyl tautomers. 

IR and Raman spectra of a series of l,2-dithiole-3-thiones and 1,2-dithiol-3-ones have been recorded and interpreted.274 Sixteen of the eighteen fundamental ring vibrations of the parent l,2-dithiole-3-thione have been observed, and most of the substituent frequencies have been assigned. 

Many carbohydrates contain the fundamental ring systems of furan and pyran (Chapter 17). 

Another important step was the discovery [4] of the value of chromatography on alumina, and the formation of trinitrobenzene adducts, for the purification and identification of azulenes. The use of these techniques led to the final elucidation of the fundamental ring-system of azulenes [4]. 

In the simplest form, for a net containing only one type of ring and node, the notation used by Wells [7,8] is n,p) where the number p is the number of links at the node and n is the smallest ring. These nets are called uniform nets. It is worth mentioning that this type of notation can be used for both 2- and 3-D nets. Thus, graphite is a 2D (6,3) net and diamond a 3D (6,4) net. Our example net, srs, is a (10,3)-net with ten nodes in the fundamental ring and three links at each node, as shown in Figure 4.4... 

A complication that may arise is that the shortest path from link a to link b has a shortcut through link c which leads back to the node. Obviously, this path is not a fundamental ring since it can be divided into two smaller rings. To... 

The smallest rings are always fundamental rings. A shortest path going from link a to link b that has a shortcut via link c is not counted as a ring... 

However, the result is somewhat different when using the vertex symbols. The 8-membered circuit for the AC pair is a part of two smaller 6-rings in AD and AC, Therefore it is not a fundamental ring and thus not counted. This is denoted by a qo or a Pair BD has one extra 6-circuit (shown in Figure 4.20) and the complete symbol is 6-6-6-6-62 (or oc). 

The Ivt-a net has vertex symbol 4-8-163 and genus 9, see Figure 6.19. Note the difference in tlie Schlafli symbol and the vertex symbol. The 10-gons in the Schlafli symbol arc circuits containing shortcuts while the 16-gons are the smallest fundamental rings. 

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