Class III charges

A hallmark of Class II and Class III charges is that they are derived from analysis of computed wave functions and physical observables, respectively. Thus, to the extent that an employed level of theory is in error for die particular quantity computed, the partial charges will faithfully reflect that error. A Class IV charge, on die other hand, is one that is derived by a semiempirical mapping of a precursor charge (eidier from a Class II or Class III model), in order to reproduce an experimentally determined observable. 

Woods et al. determined class III charges for two monosaccharides, p-D-fructopyranose and 6-thio-p-D-fructopyranose and two amino acids, N-acetyl-L-alanyl amide and N-acetyl-L-serinyl amide using a modified version of the CHELP algorithm. In the course of their work, they observed that CHELP assigned different charges when the electrostatic potential was computed from a wavefunction calculated using Gaussian 82 ° and when... 

In all cases, the variability for the PDQC charges in Table 2 is highest for the central carbon atom. As Woods et al. note, the exposure of the van der Waals surface of the methanol carbon atom is quite limited. As a result, the electrostatic potential will be more sparsely sampled in this region and perhaps therefore will not be as well described by the final parameters. Classical electrostatics is likely playing a role here as well. Classically, all the charge on a charged object is found on the surface of the object. Because class III charge... 

Figure 6 Magnitude of the range of class III charges in glycerylphosphorylcholine. In the accompanying atom numbering scheme, hydrogens have been omitted for clarity. (Data from Ref. 26.)...

The equivalent charge weight of TNT is calculated on the basis of the entire cloud content. FMRC recommends that a material-dependent yield factor be applied. Three types of material are distinguished Class I (relatively nonreactive materials such as propane, butane, and ordinary flammable liquids) Class II (moderately reactive materials such as ethylene, diethyl ether, and acrolein) and Class III (highly reactive materials such as acetylene). These classes were developed based on the work of Lewis (1980). Energy-based TNT equivalencies assigned to these classes are as follows ... 

It is interesting to note that these complexes are mixed-valent MnmMnIV complexes. Based on the relative structural data [the bond distances of the MnA atom are shorter than those of MnB], it has been concluded that in [Mn202(bipy)4]3+ one of the manganese ions is in the oxidation state IV [Mn(B)] and the other in the oxidation state III [Mn(A)]. Hence, the complex would have to be classified as a mixed-valent derivative with localized charge (Robin-Day Class I). Conversely, the two manganese sites are identical in [Mn202(phen)4]" +, from which one can infer that the charge is delocalized over the two centres (Robin-Day Class III). 

Class III safety explosives must be safe in a 9% methane-air mixture when fired with the maximum number of cartridges that can be placed in a row in the 2 m long groove of the angle-shot mortar. The experiment starts with 1800 g charge. It is increased by 200 g increments. The charge limit is determined this should not give any inflammation in five consecutive shots. 

In the extreme class III behaviour,360-362 two types of structures were envisaged clusters and infinite lattices (Table 17). The latter, class IIIB behaviour, has been known for a number of years in the nonstoichiometric sulfides of copper (see ref. 10, p. 1142), and particularly in the double layer structure of K[Cu4S3],382 which exhibits the electrical conductivity and the reflectivity typical of a metal. The former, class IIIA behaviour, was looked for in the polynuclear clusters of copper(I) Cu gX, species, especially where X = sulfur, but no mixed valence copper(I)/(II) clusters with class IIIA behaviour have been identified to date. Mixed valence copper(I)/(II) complexes of class II behaviour (Table 17) have properties intermediate between those of class I and class III. The local copper(I)/(II) stereochemistry is well defined and the same for all Cu atoms present, and the single odd electron is associated with both Cu atoms, i.e. delocalized between them, but will have a normal spin-only magnetic moment. The complexes will be semiconductors and the d-d spectra of the odd electron will involve a near normal copper(II)-type spectrum (see Section 53.4.4.5), but in addition a unique band may be observed associated with an intervalence CuVCu11 charge transfer band (IVTC) (Table 19). While these requirements are fairly clear,360,362 their realization for specific systems is not so clearly established. 

Because the ground state is delocalized between metal ions, it is not strictly appropriate to describe the intervalence transition band of a class III complex as a metal-to-metal charge transfer transition. Nevertheless, the MMCT designation will be used for the sake of simplicity. 

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