Ring-size designator

If a cyclic form is to be named, the locants of the anomeric centre and of the carbon atom bearing the ring oxygen atom must be given (in that order) (cf. 2-Carb-6.4). If there is more than one ring size designator, they are placed in alphabetical order (e.g. furanose before pyranose). 

The compounds usually known as monosaccharide anhydrides or glycose anhydrides (earlier glycosans ), formation of which involves the anomeric hydroxy group, are named by the same procedure. In these cases the order of preference of ring size designators is pyranose > furanose > septanose. However, three- or four-membered rings should normally be cited as anhydro if there is a choice. 

Ring Connectivity Ring Size Designator Frequency... 

For the cyclic hemiacetal forms of these sugars the position of the ring-size designator depends upon which carbonyl group participates in ring for-... 

Table 6.1 Ring Size Nomenclature of Medium-Sized Rings Hydrocarbon Ring-Size Designator...

Framework designation Topology Ring size Pore diameter, nm... 

In Pedersen s first full paper on the synthesis of macrocyclic polyethers, he reported the synthesis of thirty-three macrocycles having a variety of ring sizes and substituents. These compounds were prepared by a variety of routes and Pedersen offered a scheme in which he generalized the synthetic approaches he used. He designated the four principal methods V , W , X , and Y . The methods are diseussed individually. 

There is no separate shift conversion system and no recycle of product gas for temperature control (see Figure 1). Rather, this system is designed to operate adiabatically at elevated temperatures with sufficient steam addition to cause the shift reaction to occur over a nickel catalyst while avoiding carbon formation. The refractory lined reactors contain fixed catalyst beds and are of conventional design. The reactors can be of the minimum diameter for a given plant capacity since the process gas passes through once only with no recycle. Less steam is used than is conventional for shift conversion alone, and the catalyst is of standard ring size (% X %= in). 

Crown ethers are cyclic polyethers designated [n]crown-m where n is the ring size and m the number of oxygen atoms, for instance [18] crown-6 1. They show a high affinity for cationic guest molecules, especially alkali metal cations, where the cation is commonly complexed within the cavity of macrocycle or sand-... 

This method is useful when dealing with simple heterocycles, but it can become clumsy with more complex ones. An alternative is the Hantzsch-Widman system, which uses the same prefixes, but adds a stem name designed to indicate not only the ring size but also the state of unsaturation or saturation (note when the stem name begins with a vowel the last letter, a, of the prefix is dropped). The stem names for rings containing up to 10 atoms are shown in Table 1.1. 

In contrast to considerations of 50 years ago, today carbene and nitrene chemistries are integral to synthetic design and applications. Always a unique methodology for the synthesis of cyclopropane and cyclopropene compounds, applications of carbene chemistry have been extended with notable success to insertion reactions, aromatic cycloaddition and substitution, and ylide generation and reactions. And metathesis is in the lexicon of everyone planning the synthesis of an organic compound. Intramolecular reactions now extend to ring sizes well beyond 20, and insertion reactions can be effectively and selectively implemented even for intermolecular processes. 

---