Preferred representations

Note The preferred representation is with the phenyl group in the 1 - position, i.e. that which corresponds to the name poly(l-phenylethane-1,2-diyl) [2],... 

Note The preferred representations for these constitutional units are with the heterocyclic rings leftmost [2]. 

Note The preferred representations for the constitutional units from 6-aminohexanoic acid and 7-aminoheptanoic acid are -NH-CO-(CH2)s- and -NH-C0-(CH2)6-, respectively [2]. 

Note 1 The preferred representations for the constitutional units are -CH(C6H5)-CH2- and -CH(4Cl-C6H4)-CH2-[2] use of the preferred representations would result in a-pentyl and co-[l-carboxy-l-(4-ehlorophenyl) methyl] end-groups. 

The fact that several representations are possible automatically necessitates the development of rules which would allow a researcher to decide upon a preferred representation. To this end, lUPAC has developed an elaborate rules-based system using the seniority of subunits , the direction of citation, etc. [65]. However, rules-based systems are subject to the same limitations as nomenclature systems in that they, too, suffer from (potential) historical discontinuities and require acceptance by a broad community. 

For example, of the three possible electronic structures for naphthalene, the symmetrical structure (a) with two benzenoid rings (aromatic sextets) would be the more stable, and hence the preferable representation. 

With propylene, attack by Cl ion on the corresponding cyclic intermediate would not produce the observed product. An open carbonium ion is therefore the preferred representation for acyclic olefin intermediates (Eq. 144). 

Functions of a single variable, involving a relation between two sets of numbers, may be expressed in terms of a table (expressing an association), formula, prescription or graphical plot. For functions of two independent variables (see below), the preferred representations are formula, prescription or graphical plot for three or more variables, a formula or prescription is the only realistic representation. 

The preferred representation of the Figure 14.5 structure may be as a mixture of the E and Z geometric isomers because they can interconvert via other tautomeric intermediates. Related to tautomer canonicalization is the ability to identify tautomers by exact or substructure querying of the... 

Let us first assume that the reduced density operator p(0) can be chosen to be diagonal in the preferred -representation (which corresponds to the usual random phase approximation at t = 0). Then each term of Eq. (29) is of the form... 

Here Sv is the permittivity of vacuum (= 8.854 x 10 Fm ) and Co is the geometrical capacitance of the sample. The dielectric properties of polymers are variously reported in terms of Z, Y, s, M, a and its reciprocal, the resistivity p. This is a source of confusion and makes it difficult to compare literature data for different polymer materials. The preferred representations of data when dipole polarization and ion conductivity are present will be indicated below. 

The scientific community prefers representations by source-based names because they are easier to generate and to use. In general, the use of structure-based nomenclature is preferred by the lUPAC. 

---