Model nucleophiles

In Eq. (10-17), parameters a and b measure the sensitivity of the reaction to these nucleophilic parameters. Since H measures proton basicity and En the electron-donation ability, this treatment models nucleophilicity as a combination of electron loss and electron pair donation. The Edwards equation is thus an oxibase scale of nucleophilic reactivity. Table 10-5 summarizes the nucleophilic parameters. 

Addition of ammonia as a model nucleophile to nitrile oxides was studied by a semiempirical MNDO method, for fulminic acid and acetonitrile oxide (121). The reaction is exothermic and proceeds in two steps. The first (and rate-determining) step is the formation of a zwitterionic structure as intermediate. The second step, which involves transfer of a proton, is very fast and leads to the formation of Z-amidoximes in accordance with experimental data. Similar results were... 

The calculations also suggest why tram addition of nucleophiles to alkynes is invariably observed, and why the apparently unusual trajectories proposed by Baldwin48 for such attacks occur. Table 3 shows the energy changes which occur upon various distortions of acetylene and ethylene, as well as energies of interaction of the various geometries of these species with hydride ion, a model nucleophile. 

Beck, J.M., Hadad, C.M. (2008). Hydrolysis of nerve agents by model nucleophiles a computational study. Chem. Biol. Interact. May 2. (Epub ahead of print)... 

Fliege, R. and Metzler, M. 2000. Electrophilic properties of patulin. Adduct structures and reaction pathways with 4-bromothiophenol and other model nucleophiles. Chem. Res. Toxicol. 13, 363-372. Florianowicz, T. 2001. Antifungal activity of some microorganisms against Penicillium expansum. Eur. Food Res. Technol 212, 282-286. 

Since by definition the overall TS for SN1 -like mechanisms is ionization, facial selectivity (which leads to stereospecificity) is thought to depend on the facial specificity of the post-TS nucleophile-carbenium ion encounter complex.104 Little is known at present about the possible structures of CIPs or SSIPs. However, the free oxacarbenium ions can be modeled by QM as already shown. By extending these studies to allow model nucleophiles (typically methanol), to complex with one face or the other, it may be possible to find models of such encounter complexes. Such a study... 

Semenov, S. G., and N. V. Khodureva. 1992. Quantum-chemical estimate of nonspecific solvent effect on the electronic structure and spectra of molecules modeling nucleophilic fragments of lignin. Opt. Spektrosk. 73(2) 280-290. 

O2 binding for monooxygenase models Nucleophile binding for esterase model... 

The mechanistic picture elaborated for the VNS with carbanion of chloromethyl phenyl sidfone as a convenient model nucleophile is valid for other carbanions. 

By contrast, a satisfactory correlation was obtained (equation 9) with the pseudo first-order reaction rate velocity with the model nucleophile NBP (p-nitrobenzylpyridine). 

Adsorbed CO with Ionised H2 Hydride Model Nucleophile... 

Fig. 5.1 Stretched surface H2 giving hydride ion as model nucleophile to attack adsorbed CO...

Note that this assumes a collision occurs in the gas phase. The collision dynamics has not been investigated here. In the adsorbed phase, the moleeules may be physisorbed and consequently fixed in the vicinity of the surface. Reagent molecule co-adsorption is considered, in which the model nucleophile and CO are adsorbed at the surface and close to each other. This is by no means unlikely, since CO tends to adsorb strongly at temperatures up to a few hundred K, whereas the hydrogen atoms diffuse readily. See [30]. Below the DMC standard error (se) are considered. 

Marquet, J., Rafecas, L., Cantos, A., Moreno-Mahas, M., Cervera, M., Casado, E, Nogu s, M.V., and Cuchillo, C.M., The search for biochemical photoprobes. 111. The photoreactions of 4-nitro-veratrole and 2-fluoro-4-nitroanisole with Bovine Pancreatic Ribonuclease A and with model nucleophiles. Tetrahedron, 49, 1297, 1993. 

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