Structural instability, 0-0 bonding interactions

The application of this model to polydiacetylenes ( ) leads to different results since the chain structure must be different on either side of the defect, as shown in Figure 15. Bond-alternation defect must, therefore, be created in pairs at either end of a polybutatriene sequence. The creation of the new chain structure will require considerable energy and will be hindered by bulky, interacting side-groups. Thus, they are liable to be few in number, and, in view of the higher energy intrinsic and the relative instability of the polybutatriene structure, will be metastable. The occurrence of such defects will be favored in partially crystalline materials with small side-groups such as... 

Table 1 shows the comparison of ice VIII and ice Vlll-Iike structures notice that the instability of the ice VIII structure is not apparent from the hydrogen bond BCP data as the values are similar for both structures. The difference is very apparent in the O—O BCP data, especially in the values of the ellipticity s, for the F and F-like, G and G-like BCPs. The F and G O—O interactions feature very prominently in the zone centre modes with symmetry coordinates Vtx, V/rEg and v/zAi [16]. 

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