Methane bonds

Figure 1.2 The tetrahedral structure of methane. Bonding electrons in methane principally occupy the space within the wire mesh.

For those familiar with polymer chemistry, polyurethane may be a confusing term. Unlike polyethylene, the polymerization product of ethylene, a polyurethane is not the result of the polymerization of urethane. To add to the confusion, a urethane is a specific chemical bond that comprises a very small percentage of the bonds of a polyurethane. Since we are interested in chemical and physical effects, polyether or polyester is a more descriptive term for the most common bond in a polyurethane. Despite this complication, it is instructive to begin by talking about the methane bond from which the polyurethane name is derived. The general structure or bond that forms the basis of this chemistry is the urethane linkage shown in Figure 2.1. 

Table 1.16. Bond Critical Points, Charge Density, and Methanes Bond Angles for Substituted...

The radius r of the collision complex can be calculated from its moment of inertia. For the ratio of preexponents one finds Vj/Vhs > 0.5. The high value of the preexponent implies that the transition state is a relatively loose one, as the interaction between CH4 and nickel results in low values for the frequencies of the NiC and NiH bonds, which reduces the corresponding partition functions relatively little, because they replace the strong methane bonds. The preexponential for methane dissociation on a surface cluster is lower, however, the ratio Vt/vhs drops from 0.5 to 0.01. 

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