Average H-bond energy

Table 5.20. Cooperative (n-dependent) properties of linear formamide chains (see Figs. 5.19 and 5.27), showing the incremental binding energy AEn, average H-bonded Ron and Rmi distances, and partial charges Q and Qn on terminal monomers of the (H2NCHO) chain (for comparison, the cyclic pentamer in Fig. 5.27(c) has Ro u = 1.879 A, Rm = 1-024 A, and average H-bond energy 7.92 heal mol x)...

An interesting aspect of cooperativity, and one that has seldom been probed, is how this property is affected by solvation. In order to examine this question, the various H-bonded chains were next immersed in various solvents, each represented by a continuum with the dielectric constant e characteristic of that solvent. Table 15-7 reports the average H-bond energy (computed as the energy required to break the n-mer apart into n separate monomers, divided by the number of H-bonds in the chain) for dielectric constants varying from unity (vacuum) up to 78 to represent aqueous solution. 

The bond energy and bond-dissociation energy are the same for the bond in a diatomic molecule but are different for a bond in a polyatomic molecule. For example, the bond-dissociation energy for the O—H bond in the water molecule (splitting H20 into H + OH) is 119.9 kcal/mole and that for the O—H bond in the OH radical is 101.2 kcal/mole. Their average, 110.6 kca.l/mole, is the O—H bond energy. 

It is important io recognize that the bond energies listed in Table 4-3 for all molecules other than diatomic molecules are average values. That the C-H bond energy is stated to be 98.7 kcal does not mean that, if the hydrogens of methane were detached one by one, 98.7 kcal would have to be put in at each step. Actually, the experimental evidence is in accord with quite different energies for the separate dissociation steps ... 

The O—H bond energy thus calculated (110 kcal) is an average value ... 

The average value for the C—H bond energy, 99 k al, is thus one fourth the energy released in the reaction C + 4H —> CH, that is, the formation of methane from the free atoms in the gaseous state. 

Given this structure, it is natural to envision four individual C—H interactions (we call them bonds). The energy of stabilization of CF14 is divided equally among the four bonds to give an average C—H bond energy per mole of C—H bonds ... 

TABLE 5 Mean Percentage Deviation of the Average H-Bond Length and Energy (Table 2) from the Values Obtained for All of the Optimized Clusters... 

We should keep in mind that each of the values listed is the average bond energy from a variety of compounds. The average C—H bond energy is 413 kJ/mol of bonds. Average... 

Firstly, we calculated the vector of averaged effective H-bond energies Ue//k) and the matrix of averaged interactions of opposite molecules in hexagonal cycles Uopp(m,n). Total energy per unit cell to third neighbor interaction accuracy is... 

In order to investigate the effect of SHB in CHQ nanotubes, we have performed calculations with the increasing number of H-bonds. On the basis of exponential decay plot, the asymptotic H-bond energies for fV > gh> Qb > Qb, and Qb > fV in infinite H-bond relay are estimated to be 11, 11, and 12 kcal/mol, respectively. The average value of these H-bond energies is... 

Using the following information and the fact that the average C—H bond energy is 414kJ/mol, estimate the standard enthalpy of formation of methane (CH4). 

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