Bonding design factors

The technique most often used (i.e., for an atom transfer) is to hrst plot the energy curve due to stretching a bond that is to be broken (without the new bond present) and then plot the energy curve due to stretching a bond that is to be formed (without the old bond present). The transition structure is next dehned as the point at which these two curves cross. Since most molecular mechanics methods were not designed to describe bond breaking and other reaction mechanisms, these methods are most reliable when a class of reactions has been tested against experimental data to determine its applicability and perhaps a suitable correction factor. 

If most of the particles are less than ca 0.6 cm in size, flow obstmctions can occur by physical, chemical, or electrical bonds between particles. This cohesiveness is characterized by the bulk material s flow function. The forces acting to overcome a cohesive arch and cause flow are described by a hopper s flow factor, which can be obtained from the design charts (see Fig. 7). The minimum opening size required to prevent a cohesive arch from forming can be calculated from the comparison of the flow factor and flow function. 

Heat resistance is iafluenced by both the type and extent of cure. The greater the strength of the chemical bonds ia the cross-link, the better is the compound s heat resistance. Peroxide cure systems, which result ia carbon—carbon bonds, result ia a range of sulfur cross-links varyiag from 1 to > 30 sulfur atoms per cross-link, and heat resistance improves as the number of more thermally stable short cross-links predominates. This is an important factor ia designing the desired cure system. 

All the above-mentioned acyclic 1,3-diradicals are less stable than the a-bonded isomers. Therefore, in addition to using various substituents, other factors should be further considered in our design of persistent singlet 1,3-diradicals. In Sect. 5.2, ring structure is taken into account. Strain prevents the ring closure in the singlet state. Two linkers between the radical centers multiply the through-bond interactions. 

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