Planar nomenclature

Cyclazines are conjugated cyclic molecules in which planarity is secured by three covalent bonds to a central nitrogen atom. They differ in the size of the individual ring units. In the nomenclature of cyclazines, the name is preceded by the number of jt-centers between the points of attachment to the nitrogen which are arranged by increasing number and put in brackets, e.g. [3.3.3]cyclazine (1) and [2.3.4]cyclazine (2). 

The Haworth representation implies a planar ring. However, monosaccharides assume conformations that are not planar these may be represented by Haworth conformational formulae. The nomenclature of conformations is described in 2-Carb-7. For example, (5-D-glucopyranose assumes a chair conformation ... 

Syndiotactic polystyrene (sPS) is a semicrystalline polymer, which shows four different forms, namely, a, [>. y, and <5, according to the nomenclature proposed by Guerra et al.41 The first two forms, a and />. have a //Y/n.v-planar conformation of... 

The cis-tram stereodescriptors are acceptable for simple organic structures and they have been used also to describe spatial distribution in octahedral and square-planar structures. However, they are not adequate to distinguish all possibilities. The system that is currently recommended for complexes is described in more detail in the Nomenclature of Inorganic Chemistry, Chapter 10. 

Geometrical descriptors, such as cis, trans, mer (from meridional) and fac (from facial), have found wide usage in coordination nomenclature. The meaning is unequivocal only in simple cases, particularly square planar for the first two and octahedral for the others. 

The three isomers are cis/trans isomers with respect to the substituents -phenyl and -0-0 at C-4, and -OC2H5, = 0 at the P atom. For convenience, we use the E/Z nomenclature recommended for ethylene diastereoisomer assignment. If we replace the plane in ethylenes through the sp and sp atoms by a plane vertical to the phosphacyclohexadiene (2,4) ring (thought of in first approximation as planar) through C—4 and the phosphorus atom, we have to denote the isomer with -0—0 at C—4 and = O at P on the same side of this plane as Z , and that with -0-0 at C—4 and -OC2H5 at P on different sides as E diasteroisomer. 

Schemes 3 and 4 show the topological arrangements for trien in both octahderal and square planar (trans) geometries. These stereochemical arrangements are available for any of the linear tetramine ligands (50)—(56), but the R,S nomenclature must be assigned for each individual polyamine. The R,S nomenclature shown in Scheme 3, applicable to trien and 3,2,3-tet, must be systematically reversed for 2,3,2-tet.

An important observation of the above two naming schemes for fisular compounds is that there has been no usage of, nor reliance or reference to, the smallest set of smallest rings [54], or any other inappropriate planar measure of an essentially linear set. Consequently, the question raised in an earlier study [55] as to whether the nomenclature for... 

In Chapter 2, the use of a bonds for one special bonding that occurs in one particular boron compound, which was called "diborane", was introduced. An examination of other boron compounds and the nomenclature associated with them is now undertaken. First of all, it should be noted that despite that boron has three electrons in its outer shell and that a trigonal planar bonding pattern is common in molecules such as BF3, etc., the simplest hydride of boron that is normally encountered is not BH3. To the contrary, under normal conditions of temperature and pressure, not only is the smallest boron hydride a dimer, but also two distinct diboron hydride molecules are encountered. 

---