Solvolytic reaction

Solvolytic Reactions.—further study is reported of the curious formation of the 3j8,5)5-oxetan (100) by solvolysis of the (cis)-3, 5)S-diol monotosylate (99). The (trans)-3o,5j8-diol 3-tosylate solvolyses at only 1/19 the rate found for the cis-isomer. Only the latter gives the oxetan, and the higher rate is thought to result largely from relief of steric compression, rather than from anchimeric 

Komeno, S. Ishihara, H. Itani, H. Iwakura, and K. Takeda, Chem. andPharm. Bull. Japan), 1969,17,2110. 

A fragmentation reaction occurred when the tosylate (101) of 4jS,5-epoxy-5)3-cholestan-3jS-ol was treated with either collidine or lithium carbonate-dimethyl-formamide, giving the diene-ether (102) among other products. Side-chain 

Rates of solvolysis of the tosylates of 3a- and 3 -hydroxy-5a-cholestanes, and their 6-dehydro- and 7-dehydro-derivatives, showed a significant entropy effect.Equatorial (3 ) tosylates solvolysed in acetic acid, or a mixture of 

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Fonnation of allylic products is characteristic of solvolytic reactions of other cyclopropyl halides and sulfonates. Similarly, diazotization of cyclopropylamine in aqueous solution gives allyl alcohol. The ring opening of a cyclopropyl cation is an electrocyclic process of the 4 + 2 type, where n equals zero. It should therefore be a disrotatory process. There is another facet to the stereochemistry in substituted cyclopropyl systems. Note that for a cri-2,3-dimethylcyclopropyl cation, for example, two different disrotatory modes are possible, leading to conformationally distinct allyl cations ... 

Most of the kinetic measures of solvent effects have been developed for the study of nucleophilic substitution (Sn) at saturated carbon, solvolytic reactions in particular. It may, therefore, be helpful to give a brief review of aliphatic nucleophilic substitution. Two mechanistic routes have been clearly identified. One of these is shown by... 

In 1955 Swain, et al. proposed a four-parameter equation, Eq. (8-74), to describe the solvent dependence of solvolytic reactions. 

As mentioned above in the introductory section, this survey will be selective rather than all-inclusive. To begin with, some early work on isotope effects in solvolytic reactions which was interpreted in steric terms, and which in part actually pre-dates the treatment of BarteU (1960, 1961a, b) will be reviewed. 

In solvolytic reactions like those we have just been considering, where the solvent itself is the nucleophile, such mixed kinetics may not be detectable, irrespective of what is actually happening, as both SN1 and Sn2 pathways are likely to follow a rate equation of the form ... 

In contrast, the non-fusible coal requires the solvation (extraction) or solvolytic reaction to be liquefied. The solvation of non-polar organic compounds including the pitch may be rather limitted, so that the solvolytic reaction is necessary for the high liquefaction yield between the coal and the solvent. 

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. 

For micelle-assisted bimolecular non-solvolytic reactions it is necessary to consider both medium and proximity effects. 

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. 

These structures were then used to generate the force fields and calculate the secondary /3-deuterium-d6 equilibrium isotope effects (EIEs) for the formation of the isopropyl carbocation (Table 30). Because the transition states for formation of the carbocation will be close to the structure of the carbocation, these KIEs should be excellent approximations of the maximum secondary /3-deuterium KIEs expected for the limiting SN1 solvolytic reaction. 

It is clear that these solvolytic reactions of ipso-adducts are markedly dependent on reaction conditions strongly acidic conditions and electron withdrawing substituents will favour a heterolytic process lower acidity, higher temperatures and electron releasing substituents probably favour homolytic processes. With so many factors involved, each substrate under each set of conditions gives rise to its own particular behaviour. 

Measurement of reaction rate and activation parameters showed that in solvolytic reactions the [2.2]paracyclophanyl system is a much more active neighboring group than is the phenyl nucleus in its open-chain counterparts 101 a and 101b Aryl participation (charge delocalization) is greater in paracyclophanyl bromide (100a) than in 101 a. 

Fig. 9.1. Simplified reaction mechanisms in the hydrolytic decomposition of organic nitrates. Pathway a Solvolytic reaction (Reaction a) with formation of a carbonium ion, which subsequently undergoes SN1 addition of a nucleophile (e.g., HO ) (Reaction b) or proton E1 elimination to form an olefin (Reaction c). Pathway b HO -catalyzed hydrolysis (,SN2). Pathway c The bimolecular carbonyl-elimination reaction, as catalyzed by a strong base (e.g., HO or RO ), which forms a carbonyl derivative and nitrite.

Acid-induced wagner-meerwein rearrangements in chiral alcohols. In view of the considerable interest on ion-molecule complexes involved in gas-phase analogues of solvolytic reactions," ° " a sustained research effort has been directed to the study of Wagner-Meerwein rearrangements in cationized )8-arylaIkyl systems, under conditions excluding nucleophilic assistance by the solvent which in these systems normally interferes with anchimeric assistance of groups adjacent to the... 

Some obscure facets of this intricate picture have been unveiled by Filippi and Speranza who investigated the stereochemistry and the intimate mechanism of a model solvolytic reaction taking place in an ion-dipole pair in the gaseous phase. ° Adducts (7 )-56 and R)-51 are obtained in the gas phase by association of the relevant chiral alcohols, i.e., (/ )-(- -)-l-phenyl-ethanol ((I )-44) and (/f)-(- -)-l-(pentafiuorophenyl)ethanol K)-55), with the CHs OHJ ion, generated by y-radiolysis of CH3F/H2 0 mixtures (Scheme 24). As mentioned above, the absence of neutral nucleophile molecules, i.e., CH3 OH, in the reaction medium ensures that the 0-labeled ethers 45 and 58 of Scheme 24 arise exclusively from the intracomplex solvolysis of R)-56 and R)-51, respectively. 

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