Bond dissociation energy data trends

However, quantitative yield determinations of the products have not yet been carried out. Although additional kinetic data are required for the CIO + DMS and BrO + DMS reactions, the trend of rate constants obtained for the XO + DMS reactions (X = I, Br, Cl) is in good agreement with the thermodynamics. Assuming the mechanism discussed above, the reactivity of XO radicals with DMS decreases with increasing X-O bond dissociation energy E (X-O) = 41.S, SS.l and 63.4 kcal mole 1 for A = I, Br, Cl, respectively, which of course also lowers the reaction enthalpy in the same order for the respective reactions. 

Table 1 summarizes the trends in the structures and bond dissociation energies of hydrides (MH , n = 1, 2 and 3 for M = As, Sb and Bi) calculated with the CASSCF/CI method together with the available experimental data. The spectroscopic properties and potential energy curves for monohydrides (MH) have been fully summarized by Balasubramanian. Even for simple hydrides, there are only few experimental data for comparison. As Table 1 shows, however, good agreement is seen between the calculated and limited experimental values. This will permit the periodic trends to be discussed on the basis of the calculated values. 

Cotton and Jenkins (2) also reported bond dissociation energies for LiOH(g), KOH(g), and NaOH(g) which are in good agreement with JANAF enthalpy of formation data (7 ) for these hydroxides. Furthermore, the position of the hydroxides in the order of increasing bond dissociation energy established from their data, i.e. NaOH < KOH < RbOH < CsOH < LiOH, is that predicted by comparison with similar data on the stabilities of the alkali metal halides (8), However, trends within the bond... 

We must also consider the relative reactivities of the bonds. In the absence of direct data, we can compare bond dissociation energies as a measure of relative reactivity. Table 11-3 shows some pertinent data collected from various sources [18, 19, 20, 21]. The carbon-sulfur dissociation energies for n-alkyl monosulfides and n-alkyl mercaptans lie within a narrow range. Whether the other sulfur linkage is to carbon, as in n-alkyl monosulfides, or to the hydrogen of a mercaptan has no major influence. There is a small but perceptible trend toward weaker bonding with secondary carbon (isopropyl) and with tertiary carbon (t-butyl) in the unsymmetrical methyl aryl monosulfides, a trend that is not firmly evident in the in the corresponding alkyl mercaptans. The vinyl-sulfur... 

Computational chemistry has reached a level in which adsorption, dissociation and formation of new bonds can be described with reasonable accuracy. Consequently trends in reactivity patterns can be very well predicted nowadays. Such theoretical studies have had a strong impact in the field of heterogeneous catalysis, particularly because many experimental data are available for comparison from surface science studies (e.g. heats of adsorption, adsorption geometries, vibrational frequencies, activation energies of elementary reaction steps) to validate theoretical predictions. 

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