Solvolytic mechanism

Racemization of chiral a-methyl benzyl cation/methanol adducts. The rate of exchange between water and the chiral labeled alcohols as a function of racemization has been extensively used as a criterion for discriminating the Sn2 from the SnI solvolytic mechanisms in solution. The expected ratio of exchange vs. racemization rate is 0.5 for the Sn2 mechanism and 1.0 for a pure SnI process. With chiral 0-enriched 1-phenylethanol in aqueous acids, this ratio is found to be equal to 0.84 0.05. This value has been interpreted in terms of the kinetic pattern of Scheme 22 involving the reversible dissociation of the oxonium ion (5 )-40 (XOH = H2 0) to the chiral intimate ion-dipole pair (5 )-41 k-i > In (5 )-41, the leaving H2 0 molecule does not equilibrate immediately with the solvent (i.e., H2 0), but remains closely associated with the ion. This means that A inv is of the same order of magnitude of In contrast, the rate constant ratio of... 

It is generally agreed that the mechanism of the solvolysis of benzyl halides lies near the region which marks the transition from Sjfl to Sjf2 solvolysis. Considerations of the kinetic chlorine isotope effect have recently led to the conclusion that even 4-nitrobenzyl chloride undergoes Sul solvolysis (Hhl and Pry, 1962) but an examination of the data suggests that this effect does not represent a sensitive test of solvolytic mechanism (Kohnstam, 1967). On the other hand, the values oi AC, AC I AS, and AS show that the solvolysis of the parent compoimd has the characteristic featvues of an 8 2 reaction (Tables 5, 6), and other evidence also supports this conclusion (see Bensley and Kohnstam, 1957). 

Andres, J., Arnau, A., Silla, E., Bertran, J., Tapia, O. Atheoretical study of the intramolecular solvolytic mechanism of the Meyer-Schuster reaction. MINDO/3 and CNDO/2 calculations of minimum energy paths. THEOCHEM1983, 14,49-54. 

The analysis of the first two mechanisms showed the solvolytic mechanism as the most favorable localizing itself during the reaction path to an alquinylic carbocation interacting electrostatically with a molecule of water. This fact has been supported by the experimental detection of alquinylic carbocations in solvolytic conditions. Things being like that, two alternatives remain for the slow stage of the Meyer-Schuster reaction, the solvolytic and the intermolecular mechanism, and it seems that the solvent has a lot to say in this. 

For the step which limits the reaction rate (rate limiting step), three mechanisms have been proposed, two of which are intramolecular - denominated intramolecular, as such, and solvolytic - and the other intermolecular (Figure 2.1.18). The first of these implies a covalent bond between water and the atoms of carbon during the whole of the transposition. In the solvolytic mechanism there is an initial rupture from the O-C, bond, followed by a nucleophilic attack of the H2O on the C3. Whilst the intermolecular mechanism corresponds to a nucleophilic attack of H2O on the terminal carbon C3 and the loss of the hydroxyl group protonated of the C. ... 

Since the rates of the replacement reactions studied are independent of the nucleophilic ligands they must proceed via a rate-determining step to a reactive intermediate. This may be the five-coordinate [Rhen Xp dissociative mechanism) or the six-coordinate [Rhen XH O] (Sj 2 solvolytic mechanism). Since the reactions are reversible, they can be written as in 2 where k +Y... 

The toluenesulphonylmethyl ketones (304) react with methanolic hydroxide to give a product mixture containing bicyclo[3,2,0]heptane derivatives (305) and (306). The bicyclo[3,2,0]hepten-7-ones (306) were shown to arise by rearrangement of the bicyclo[3,l,l]heptenones (307). The bicyclo[3,2,0]hepten-6-ones (305) are formed from (304) by a solvolytic mechanism. 

These results demonstrate that, within experimental error, the corresponding reaction constants for the two reactions, solvolysis and rearrangement, are the same. In other words, the two reactions have the same dependence on substituent effects, which is consistent with Scheme 8-10 because the transition state for rearrangement is identical to the first transition state in the mechanism of solvolytic dediazoniation. 

It is evident from the foregoing sections that simple alkylvinyl halides do not react via an Sn 1 mechanism, if at all, even under extreme solvolytic conditions (146,149). More reactive leaving groups, such as arylsulfonates, were clearly needed to investigate the possible solvolytic behavior of simple alkylvinyl systems, but the preparation of vinyl sulfonates until recently was unknown. Peterson and Indelicato (154) were the first to report the preparation of vinyl arylsulfonates via reaction of the appropriate disulfonate with potassium t-butoxide in refluxing f-butanol. They prepared and investigated the solvolysis of 1-cyclohexenyl tosylate 169 and c/s-2-buten-2-yl tosylate 170 and the corresponding p-bromobenzenesulfonates (brosylates). Reaction... 

The mechanism of reaction of primary vinyl triflates and the possibility of solvolytic generation of primary vinyl cations needs further exploration. Along these lines, an examination of the behavior of the simplest vinyl system CH2=CHOTf and the possibility of generating the parent vinyl cation needs to be done. 

Scheme 3.4 Proposed reaction mechanism for the deprotection and solvolytic rearrangement reactions of pHP caged phosphates like HPDP consistent with the TR, fs-TA and fs-KTRF experiments described here and in references 49 and 134.

The present results are well understood by the above mechanism. Itmann which is fusible at relatively high temperature was not liquefied below 420°C with a non-solvolytic solvent such as pyrene, however it was significantly liquefied at 480°C of its maximum fluidity temperature in decacyclene of a stable aromatic compound. 

The liquefaction mechanism was discussed by distinguishing the fusible coal from non-fusible one. The importance of solvolytic hydrogen transfer is pointed for the liquefaction of non-fusible coal under atmospheric pressure. 

The preparation of di-w-butyl ether is illustrative (Scheme 2.6). No reaction occurred with n-butanol alone for 2 h at 200 °C. However, in the presence of 10 mol % n-butyl bromide, 26% conversion of the alcohol to the ether was obtained after 1 h, without apparent depletion of the catalyst. It is known that addition of alkaline metal salts can accelerate solvolytic processes, including the rate of ionization of RX [41]. This was confirmed when the introduction of LiBr (10 mol %) along with n-butyl bromide, afforded a conversion of 54% after 1 h at 200 °C. Ethers incorporating a secondary butyl moiety were not detected, precluding mechanisms involving elimination followed by Markovnikov addition. 

Mechanisms of solvolytic reactions, medium effects on the rates and, 14,10... 

Radiation techniques, application to the study of organic radicals, 12, 223 Radical addition reactions, gas-phase, directive effects in, 16, 51 Radicals, cation in solution, formation, properties and reactions of, 13, 155 Radicals, organic application of radiation techniques, 12,223 Radicals, organic cation, in solution kinetics and mechanisms of reaction of, 20, 55 Radicals, organic free, identification by electron spin resonance, 1,284 Radicals, short-lived organic, electron spin resonance studies of, 5, 53 Rates and mechanisms of solvolytic reactions, medium effects on, 14, 1 Reaction kinetics, polarography and, 5, 1... 

Solvolytic reactions, medium effects on the rates and mechanisms of, 14,1 Spectroscopic detection of tetrahedral intermediates derived from carboxylic acids and the investigation of their properties, 21,37... 

The bromination of ethylenic compounds is in most cases a very fast reaction. Half-lives of typical olefins are given in Table 1. Most of them are very short. In order to obtain extended and meaningful kinetic data, it has been necessary to find suitable reaction conditions and to design specific kinetic techniques. This was not done until 1960-1970. As a consequence, kinetic approaches to the bromination mechanism are relatively recent as compared with those to solvolytic reactions, for example. 

Micellar rate enhancements of bimolecular, non-solvolytic reactions are due largely to increased reactant concentrations at the micellar surface, and micelles should favor third- over second-order reactions. The benzidine rearrangement typically proceeds through a two-proton transition state (Shine, 1967 Banthorpe, 1979). The first step is a reversible pre-equilibrium and in the second step proton transfer may be concerted with N—N bond breaking (17) (Bunton and Rubin, 1976 Shine et al., 1982). Electron-donating substituents permit incursion of a one-proton mechanism, probably involving a pre-equilibrium step. 

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