Anionic reactions, molecular rearrangements

The above discourse of the Perkin Reaction is self-explanatory in which benzaldehyde and acetic anhydride interacts to form an anion (I) that undergoes molecular rearrangement to give another anion (II). The resulting restructured anion (II) reacts with acetic anhydride to form an intermediate which subsequently undergoes hydrolysis in the presence of a base to give rise to the formation of an a, P-unsaturated carboxylic acid i.e., cinnamic acid. 

In order to connect the oxidation stability of the model electrolyte complexes to LSV experimental data, one needs to consider the reaction rates for the oxidation reaction of each complex. Indeed, the H-transfer reaction in the solvent-solvent or solvent-anion complexes leads to a significant molecular rearrangement and distortion thus, one expects a significant barrier for these oxidation reactions compared to the oxidation of an isolated EC. Rates for each electron transfer reaction can be estimated in a first approximation using Marcus theory of electron transfer, where the rate (k) of the activation-controlled reaction is proportional to... 

Therefore, either orbital control of the reaction or rearrangement of initially formed 1- or 3-isomers into 2-isomers takes place. As follows from quantum-chemical calculations [543,544,546], energies of highest occupied molecular orbital (HOMO) and shapes of the orbitals for the studied pyrrole anions differ slightly. Thus, the rearrangement remains the most probable explanation of the observed regiochemistry. 

Fig. 8.9 Possible mechanisms of the bioluminescence reaction of dinoflagellate luciferin, based on the results of the model study (Stojanovic and Kishi, 1994b Stojanovic, 1995). The luciferin might react with molecular oxygen to form the luciferin radical cation and superoxide radical anion (A), and the latter deproto-nates the radical cation at C.132 to form (B). The collapse of the radical pair might yield the excited state of the peroxide (C). Alternatively, luciferin might be directly oxygenated to give C, and C rearranges to give the excited state of the hydrate (D) by the CIEEL mechanism. Both C and D can be the light emitter.

The reaction of 1-chlorosiloles with alkali metals leads to unstable species that react with methyl iodide, ethyl bromide or chlorotrimethylsilane in the manner expected for the 1-silacyclopentadienide anion. Interestingly, X-ray quality crystals were isolated from the reaction with Li in THF and the molecular structure was shown to be that of a [2 + 2] head-to-tail dimer, which is formed by the 1,5-rearrangement of the anion in the silole ring185 (equation 70). 

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