Intramolecular reorganization

Even after the boron s electrophilicity has been arrested intermolecularly, intramolecular reorganization of the boraethene may still proceed. A remarkable instance is the structure 60 (by XRD) resulting from the oxidation of 57 by SnCl2. Intermediates in this impressive transformation might well be carbene 58 and boraethene 59. The borons in 59 are still sufficiently electrophilic to cause the mesityl group to bridge (Scheme l).61... 

According to experiments (Jonsson et al. 1996), the deprotonation of (Et2NH)+ takes place at the nitrogen rather than at the a-carbon. However, Costentin and Saveant (2004) showed that if a stabilized carboradical can be produced, some intramolecular reorganization takes place and a proton leaves the carbon, not the nitrogen. The formation of the amine-substituted allyl radical is just the case +NH2-CH2=CH-CH2H H+ -f NH2CH2=CH-CH2 . 

The conclusions reached by Costentin and SavOant are in fact quite consistent with our own. The main difference is that, according to these authors, the notion of an imbalanced transition state should be placed within the context of charge localization-delocalization heavy-atom intramolecular reorganization rather than of synchronization (or lack thereof) between charge delocalization and proton transfer. ... 

Two remarkable intramolecular reorganizations of the Diels-Alder adducts of methyl 2-chloro-2-cyclopropylideneacetate (1-Me) onto furans should be mentioned here. In a reaction of 1-Me with 2,5-bis(trimethylsilyl)furan (263) the unstable adduct 264 underwent a spontaneous deprotection followed by ring opening to give the dioxospiro[2.5]octene derivative 265 (Scheme 76) [7 m]. The Pauson-Khand reaction of the transformed Diels-Alder adducts 70, 71 of 1-Me have been discussed above (Scheme 18), however, when the compounds endo,-exo-62 e were treated under Pauson-Khand conditions, but at higher temperature, the interesting Co2(CO)8-promoted stereoselective rearrangement, in the presence as well as in the absence of an alkyne component, has been observed. The cis- and frans-substituted 6-methylenespiro[2.4]hexanes 266 were isolated as main products in these reactions (Scheme 76) [19b]. 

A is the sum of the solvent and intramolecular reorganization energies, and AG = F(A 0 - A 0J) is the standard electrochemical Gibbs energy of the electron transfer from x = a to x = b. Parabolic dependence of AG on AG was demonstrated [viii]. Electrochemical behavior including the kinetic analysis of various ET systems was reviewed [ix]. A special type of the ET reaction is the deposition of a metal at ITIES, e.g., the deposition of Au particles by the interfacial reaction between AUCI4 in 1,2-dichloroethane and Fe(CN)6 in water [x]. 

To test these theories it is obviously necessary to concentrate on reactions that are both rapid and strongly controlled by solvent rather than intramolecular reorganization... 

Multi-temperature X-ray diffraction data for a series of spin-crossover complexes differing in cooperativity indicates that the molecule and crystal volume variations upon spin conversion are similar in all the cases irrespective of the cooperative nature of the spin conversion [47]. So, a systematic structural analysis of specifically designed spin-crossover compounds should be of utmost importance to establish correlations between intermolecular interactions and cooperativity. The comparative structural study of [Fe(phen)2(NCS)2] and [Fe(btz)2(NCS)2] where btz = 2,2 -bi-4,5-dihydrothiazine (Figure 10) represents the sole example so far reported oriented in this direction [48,49]. It illustrates the dependence of the nature of the phenomenon on the efficiency of the intermolecular contacts in transmiting the intramolecular reorganization upon spin conversion. 

As seen from Fignre 1.1.1, the overall intramolecular reorganization energy npon electron transfer consists of two terms [1-5,17-21] ... 

Overall, the intramolecular reorganization energies in tetracene (0.11 eV) and pentacene (0.10 eV) rank among the smallest values that have been calculated or measured for molecules. A smaller value of A. (0.045 eV) has been found only in the case of phthalocyanine [39]. 

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