Solvent rearrangement

Acyl-3.4-benzo-2-azabicyclo[3.2.0]hepta-3,6-dienes 1, on heating at 250-280 C for a short time without solvent, rearrange to the 1-acyl-1-benzazepines 2 (Method A).23-38 In some cases, rearrangement is accompanied by minor amounts of Ar-aeyl-l-naphthylamine and, at higher temperatures, the acylnaphthylatnine can become the major product (see Section 3.2.2.6.). In the presence of silver(I) tetrafluoroborate (Method B) rearrangement takes place at lower temperatures but the yields of benzazepine are inferior as the silver(I) ion also catalyzes the reverse reaction (see Section 3.2.2.1.). 

A number of electron-transfer reactions of biological interest have been studied using high-pressure techniques (4, 5). These include the oxidation of L-ascorbic acid by [Fe(CN)6]3- (148), [Fe(CN)5N02]3 - (149), and Fe(phen)2(CN)2] (150). The first two reactions are characterized by volumes of activation of -16 and 10 cm3 mol-1, respectively, which indicate that solvent rearrangement as a result of an increase in electrostriction must account for the volume collapse on going to... 

Fig. 14. Schematic representation of energy levels and transitions for fluorescence and related processes kic, rate constant for interval conversion fcF, rate constant for fluorescence fcISC, rate constant for intersystems crossing fc[cp> rate constant for internal conversion from triplet state kp, rate constant for phosphorescence S, energy level for the first excited singlet state after solvent rearrangement for a polarity probe in a polar solvent.

Figure 9. Femtosecond dynamics of an elementary reaction (I2 — 21) in solvent (Ar) cages. The study was made in clusters for two types of excitation to the dissociative A state and to the predissociative B state. The potentials in the gas phase govern a much different time scale for bond breakage (femtosecond for A state and picosecond for B state). Based on the experimental transients, three snapshots of the dynamics are shown with the help of molecular dynamics simulations at the top. The bond breakage time, relative to solvent rearrangement, plays a crucial role in the subsequent recombination (caging) dynamics. Experimental transients for the A and B states and molecular dynamics simulations are shown.

The cuprous-cupric electron transfer reaction is believed to be the rate-limiting step in the process of stress corrosion cracking in some engineering environments [60], Experimental studies of the temperature dependence of this rate at a copper electrode were carried out at Argonne. Two remarkable conclusions arise from the study reviewed here [69] (1) Unlike our previous study of the ferrous-ferric reaction [44], we find the cuprous-cupric electron transfer reaction to be adiabatic, and (2) the free energy barrier to the cuprous cupric reaction is dominated in our interpretation by the energy required to approach the electrode and not, as in the ferrous-ferric case, by solvent rearrangement. 

The term AGlntrasolute describes host-guest interactions and must have a favourable or, at worst, zero contribution. It involves contributions from hydrogen bonding, dipolar and van der Waals forces. AGsolvatlon describes solvent effects (hydrophobic, solvent rearrangement). This may be favourable or... 

The orfAo-Claisen rearrangement, a no-mechanism type of reaction, is included here since it is, effectively, an alkylation reaction though not an electrophilic substitution. Two reports have recently appeared describing the rearrangement of 2-allyloxypyridines in tertiary amine solvents or in the absence of a solvent. Rearrangement... 

The acids are chosen so as to illustrate the main effects on the values of k3 j. Values of k13 are, in general, set by the strength of the AH bond, and can be interpreted in thermodynamic rather than kinetic terms. The simplest possible acid recombination reaction is that between the proton and the fluoride ion, which is simply a charged sphere. As expected, this reaction has the extremely high rate coefficient of 1 x 1011 1 mole-1 sec-1. Variations of rate coefficients from this value may be explained in terms of steric effects, ionic charge effects, and anion electronic and solvent rearrangement effects, the latter two usually being connected. 

In the detailed description of proton-transfer reactions, especially of rapid proton transfers between electronegative atoms, it should always be specified whether the term is used to refer to the overall process (including the more-or-less ENCOUNTER-CONTROLLED formation of a hydrogen-bonded complex and the separation of the products [see microscopic diffusion control]) or just to the proton-transfer event (including solvent rearrangement) by itself. 

Light excitation in the CT absorption bands formally leads to the transfer of an electron from the donor to the acceptor component (optical electron transfer). As a consequence, particularly when this process leads to formation of charges of the same sign in the two components (Fig. 8), one can expect destabilization of pseudorotaxane structures, followed by dethreading. In practice, however, this simple approach does not work because the back electron-transfer process is much faster than the separation of the molecular components, a process which requires extended nuclear motions and solvent rearrangement. In a particular case [24], laser flash photolysis experiments have suggested that a small fraction of the irradiated pseudorotaxane may undergo dissociation. 

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