Bond strength, reactivity with

In order to increase the capacity of a production line especially by reducing the necessary press times, adhesive resins with a reactivity as high as possible should be used. This includes two parameters (1) a short gelation time and (2) a rapid bond strength increase, and this even at a low degree of chemical curing. 

Other measures of nucleophilicity have been proposed. Brauman et al. studied Sn2 reactions in the gas phase and applied Marcus theory to obtain the intrinsic barriers of identity reactions. These quantities were interpreted as intrinsic nucleo-philicities. Streitwieser has shown that the reactivity of anionic nucleophiles toward methyl iodide in dimethylformamide (DMF) is correlated with the overall heat of reaction in the gas phase he concludes that bond strength and electron affinity are the important factors controlling nucleophilicity. The dominant role of the solvent in controlling nucleophilicity was shown by Parker, who found solvent effects on nucleophilic reactivity of many orders of magnitude. For example, most anions are more nucleophilic in DMF than in methanol by factors as large as 10, because they are less effectively shielded by solvation in the aprotic solvent. Liotta et al. have measured rates of substitution by anionic nucleophiles in acetonitrile solution containing a crown ether, which forms an inclusion complex with the cation (K ) of the nucleophile. These rates correlate with gas phase rates of the same nucleophiles, which, in this crown ether-acetonitrile system, are considered to be naked anions. The solvation of anionic nucleophiles is treated in Section 8.3. 

Think for a moment about the connection between bond strengths and chemical reactivity. In an exothermic reaction, more heat is released than is absorbed. But since making product bonds releases heat and breaking reactant bonds absorbs heat, the bonds in the products must be stronger than the bonds in the reactants. In other words, exothermic reactions are favored by stable products with strong bonds and by reactants with weak, easily broken bonds. 

In series with a constant entropy, reactivity is controlled by enthalpy changes. The interpretation is usually based on electronic effects (12-14), which do not affect the form of the transition state, but only bond strengths (116). 

A development reported recently [519] involves reduction of the cystine disulphide bonds in wool with either thioglycolic acid or tetrakis(hydroxymethyl)phosphonium chloride to form thiol groups, followed by crosslinking with bifunctional reactive dyes. This gave improved insect resistance but had adverse effects on physical properties such as strength, shrinkage and stiffness, thus limiting the potential of the process for commercial use. 

Finally — and this has to do with the nature of the bond strengths in such metal-metal bonded systems — the dimer also thermally dissociates. With a very reactive halogen atom donor,... 

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