Proper pairing, advantages

When judged in its entirety, the information currently available on the hetero[13]annulenes allows one to draw the following conclusions (i) the presence of a highly mobile lone pair such as those associated with N", NH, and S may induce the system to undergo the type of skeletal flattening that is necessary for w delocalization only when two or three trans double bonds are present, e.g., 77, 78, 87b and 80, 81, respectively but not when one such function is available, cf. 88b and (ii) the skeletal restriction imposed by the presence by two properly located acetylenic units imparts sufficient rigidity (AS0 advantage) to the system to allow... 

Like other transmission techniques, mulls can be time-consuming. The only way to know if the mull was made properly is to measure its spectrum. If the spectrum is bad, more time must be spent preparing a new sample. In a pair of skilled hands each sample will take several minutes via this technique. Using the split mull method at a minimum doubles sample preparation time. Mulls are typically used for qualitative work, but not for quantitative work since concentrations and pathlengths are difficult to reproduce with this method. The advantages and disadvantages of mulls are summarized in Table 4.4. 

In this chapter, the model of the effective ion pair interaction spreads on not less than 11 coordinate spheres has been taken as a base model of interactions between structural components. Regardless of the criticism of the model, the usage of approximation of effective pair interactions has many advantages that become conclusive during the choice of the proper... 

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