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Rearrangement reactions ionic species

An extreme case of the Cope rearrangement proceeds via dissociation to an ion-pair. [228], Complementary donor and acceptor stabilization of the ionic species is the cause for this abnormal reaction. [Pg.138]

Trialky Iboron carbene adducts have been prepared via a novel synthetic route, as shown in Scheme b. The initial first step involves reaction of BEt3 with 1,4,5-trimethylimidazole (56) to afford the BEts adduct (57), followed by deprotonation and rearrangement to give an ionic species (58). The triethyl-boron carbene adduct is generated in the final step by way of... [Pg.5773]

A third reaction described by Iffland " is the oxidation of a semicarbazone (1) to a carbamate (4) with elimination of elemental nitrogen. The reaction can be interpreted as involving initial formation of (2) via a tetravalent lead ester and donation of an acetoxyl group, as in the formation of VI above. Elimination of nitrogen gives the ionic species (3), which rearranges by a 1,2-shift to the carbamate (4). [Pg.274]

A novel route for the generation of trialkylboron-carbene complexes has been reported (34). As summarized in Scheme 4, the intial step of the reaction sequence involves the N-complexation of 1,4,5-trimethylimidazole 38 with BEts to form 39, followed by deprotonation and rearrangement of resulting ionic species to 40. The final step involves methylation with Mel to form the desired triethylboron-carbene complex, 41. Compound 41 was characterized by mass spectroscopy and H-, C-, and B NMR spectroscopy the B NMR chemical shift for 41 S -12.6) appears in the tetracoordinate boron region. The 1,4,5-trimethylimidazole 38 is also the source of an unusual boryl-borane compound, 43 (34). Treatment with BH3 thf, followed by deprotonation with "BuLi, resulted in the formation of the ionic carbene/borane complex, 42. In turn, 43 was produced via the addition of chlorobis(dimethylamino)borane to 42. Compound 43 exhibits B NMR chemical shifts at S -21.8 (BH3) and 8 27.8 (BNMe2). In related work, N-methyl-AT-borane complexes 44 and 45 have been de-... [Pg.13]

Allred and Winstein found that acetolyses of (11) and (12) are accompanied by extensive isomerization, and after 70% reaction the mixture of p-bromobenzenesulfonates is composed of 69% of (11) and 31% of (12) regardless of the starting material. This is the result of return from free ions as shown by the observation of a small common-ion rate depression and of the conversion of the p-bromobenzenesulfonates into toluene-p-sulfonates in the presence of lithium toluene-p-sulfonate. The reaction also shows a special salt effect in the presence of lithium perchlorate, yet even at high salt concentrations some isomerization is still evident. Since return from solvent-separated ion pairs such as (23) is excluded in the presence of lithium perchlorate, and since the geometry of the initially formed ionic species does not allow direct rearrangement to occur, a common, symmetrical intimate ion pair, such as (21), is implicated in the isomerization. The solvolysis... [Pg.127]

Such unimolecular ion-decomposition reactions can be viewed as another field of chemistry, but fortunately for most chemists studying this book, there are many close similarities to pyrolytic, photolytic, radiolytic, and other energetic reactions, and there are even many general similarities to condensed-phase (solution) organic reactions. The largest points of difference are that ionic and often radical species are involved in each reaction in the mass spectrometer, and their combined effects sometimes appear unusual to the organic chemist. Chemists may also question the reliability of structural relationships based on rearrangement reactions. However, many of these are based on well-established chemistry and can provide key molecular information... [Pg.51]

A substantial collection of ionic thermochemical data has been tabulated (Lias et ai 1988) and such data can be estimated for other species (Lossing and Holmes 1984 Holmes 1986). Equations 7.4 and 7.5 repeat the simple cleavage and rearrangement reactions of Figures 7.1-7.3. The thermochemical relationships for these reactions are shown in Figure 7.3 using values for the... [Pg.127]

The reaction pillar is chemical mechanisms and kinetics involving electron rearrangements in both abiotic and biotic systems. It is of practical importance to predict how quickly a reaction mixture will attain its equilibrium state. The processes may involve molecule rearrangements, molecule destruction, ionic species transformations, etc. All these mechanisms alter and influence chemical concentration gradients as well. Extensive literature can be found especially on atmospheric reactions, although much information is also available on aqueous and solid phase reactions. [Pg.605]


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Ionic reactions

Ionic rearrangements

Ionic species

Reaction species

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