Non-standard bonding numbers

The names of unsaturated compounds are derived by using appropriate substitutive nomenclature rules. Note that trivial names are also allowed for particular polynuclear species, for example, N2H4, diazane, commonly known as hydrazine. For a discussion of names of hydrides in which elements exhibit non-standard bonding numbers, see the Nomenclature of Inorganic Chemistry, p. 85. Note that for the hydrides of Table 5.1 and their derivatives, substitutive names are generally preferred. 

Where there is a choice of parent hydrides among those listed in Table IR-6.1 (or corresponding hydrides with non-standard bonding numbers, cf. Section IR-6.2.2.2), the name is based on the parent hydride of the element occurring first in the sequence ... 

IR-6.2.1 Mononuclear parent hydrides with standard and non-standard bonding numbers IR-6.2.2 Homopolynuclear parent hydrides (other than boron and carbon hydrides)... 

IR-6.2.2.2 Homonuclear acyclic parent hydrides with elements exhibiting non-standard bonding numbers... 

Where there is more than one kind of substituent, the prefixes are cited in alphabetical order before the name of the parent hydride, parentheses being used to avoid ambiguity, and multiplicative prefixes being used as necessary. Non-standard bonding numbers are indicated using the. -convention (see Section IR-6.2.2.2). An overview of the rules for naming substituted derivatives of parent hydrides is given in Section IR-6.3, while a detailed exposition may be found in Ref. 3. 

With ring atoms such as phosphorus, which can be tri- or pentavalent, a non-standard bonding number is indicated as an exponent of the Greek letter A after the locant. In the example, this is shown by (the 1993 Blue Book, p 21). 

In cases where the skeletal atoms of a hydride chain are the same but one or more has a bonding number different from the standard values defined by Table IR-6.1, the name of the hydride is formed as if all the atoms showed standard bonding numbers, but is preceded by locants, one for each non-standard atom, each locant qualified without a space by Xn, where n is the appropriate bonding number. 

Despite the completely different approach to chemical interaction, which has been followed here, the conventional standard symbols which are used to define the connectivity in covalent molecules, can also be applied, without modification, to distinguish between interactions of different order. However, each linkage pictured by formulae such as H3C-CH3, H2C=CH2, HC=CH, represents the sharing of a single pair of electrons with location unspecified. The number of connecting fines only counts bond order and may be established from the classical valence rules, e.g. v(C,N,0,F)=(4,3,2,l). Special symbols are used for non-integral bond orders, as in the symbol for benzene ... 

When a choice is needed between the same skeletal atom in different valence states, the one in a non-standard valence state is preferred for assignment of the lower locant. If a further choice is needed between the same skeletal atom in two or more non-standard valence states, preference for the lower locant or locants is given in order of decreasing numerical value of the bonding number, e.g. X6 is preferred to X4. 

These complexes can transform one to another (due to the water molecule diffusion or the impact of the solvent CDCI3) or change on addition of next water molecules. However, in the confined space of shallow micropores in non-standard primary particles, a possible number of molecules in the clusters (as well as the number of the hydrogen bonds per a molecule) is restricted and the molecular mobility differs from that in the larger gaps between primary particles in aggregates therefore, the NMR spectra of water adsorbed on standard (with nonporous primary particles) and non-standard fumed silicas differ markedly (Fig. 38.12). The average 8 values on transformation of these complexes correspond to... 

The accuracy of alternative Lewis structures can be assessed by specifying the number and locations of lone pairs and two- and three-center bonds with a SCHOOSE keylist (a standard option of the NBO program). (The directed SCHOOSE list replaces the usual NBO search over all possible Lewis structures, but the hybrids and polarization coefficients of CHOOSE structures are optimized in the usual way.) The increased non-Lewis density measures the larger error of the CHOOSE structure compared with the optimal NBO structure. 

FIGURE 2.1 Standard nomenclature for substrate residues and their corresponding binding sites on the protease. The subsites toward the N terminus of the substrate are called non-primed sites and are numbered SI to Sn, beginning with SI at the N terminal side of the scissile bond. The subsites toward the C terminus of the substrate are called primed sites and are numbered ST to Sn beginning with ST at the C terminal side of the scissile bond. The substrate residues that the enzymatic subsites accommodate are numbered PI to Pn and PT to Pn, respectively. 

---