2- ethyl chlorides, solvolysis

In the second, which belongs to a systematic study of the transmission of substituent effects in heterocyclic systems, Noyce and Forsyth (384-386) showed that for thiazole, as for other simple heterocyclic systems, the rate of solvolysis of substituted hetero-arylethyl chlorides in 80% ethanol could be correlated with a constants of the substituent X only when there is mutual conjugation between X and the reaction center. In the case of thiazole this situation corresponds to l-(2-X-5-thiazolyl)ethyl chlorides (262) and l-(5-X-2-thiazolyl)ethyl chlorides (263). 

Although Noyce and Fike have recently found for the solvolysis of 2-thiazolyl-ethyl chlorides analogous modality of substituent electronic effect transmission from position 2 toward position 5 and from position 5 toward position 2(60). a more general conclusion indicates that the... 

Electrophilic replacement constants crXr have been obtained for all the positions of benzo[6]thiophene from the solvolysis of isomeric l-(benzo[ >]thienyl)ethyl chlorides in 80% ethanol-water. These constants signify replacement of the entire benzene ring by another aromatic system (74JOC2828). The positional order of reactivity was determined to be 3>2>6>5>4>7, all positions being more reactive than benzene. The same order was also derived from the kinetic data for pyrolysis of the isomeric l-(benzo[6]thienyl)ethyl acetates (78JCS(P2)1053). A modified extended selectivity treatment has been developed to correlate electrophilic substitution data in benzo[Z> ]thiophene, which assumes a dual activation mechanism (79JOC724). 

Solvolysis rates of 2-(aryldimethylsilyl)ethyl chlorides were determined and the effects of aryl substituents at the silyl atom correlated with nonresonant a parameters and a p value of -1.75, reflecting the effect of the aryl ring on the bridged Si in the rate-determining step 49... 

In particular, minima in plots of AV against x2 are not necessarily due to the trend in the initial state quantity, and volumetric data can provide some indication of the details of reaction mechanism. Thus for the hydrolysis of p-chlorobenzyl chloride (Sn2), a shallow minimum in 5mAF for reaction in aqueous ethyl alcohol stems from a more intense maximum in 8m than for 5mF. At the other end of the scale, a sharp minimum in 8mAF for t-butyl chloride solvolysis (SnI) results from a sharp minimum in SmF, 5m V3 changing only gradually as x2 is increased. The behaviour of the volumetric properties for the benzyl... 

Ionization is exothermic and favored at lower temperatures in systems such as trityl, alkoxycarbenium, and benzhydryl derivatives which generate stabilized carbenium ions due to their electron-donating substituents. The exothermicity of ionization of benzhydryl species with BCl3 in CH2CI2 decreases from AH = -62 kJ/mol for di(p-anisyl) to -22 kJ/ mol for less stabilized p-tolyl and phenyl derivatives, and to approximately -8 kJ/mol for unsubstituted benzhydryl chloride [193]. These values, based on the solvolysis rates, extrapolate to AH = -12 kJ/mol for cumyl chloride (HCl adduct of a-methylstyrene) and AH = 0 kJ/mol for 1-phenyl-ethyl chloride (styrene adduct) and ( -butyl chloride (isobutene adduct) [240]. The reported entropies of ionization do not vary significantly and... 

The situation is different in alkaline solutions, in which deprotonation of the hydroxyl group can occur. In ethanol-sodium ethoxide, solvolysis of 2-chloroethanol is about 5000 times as fast as ethyl chloride. The product is ethylene oxide, confirming the involvement of the oxygen atom. 

When tert butyl bromide undergoes solvolysis in a mixture of methanol and water, the rate of solvolysis (measured by the rate at which bromide ions form in the mixture) increases when the percentage of water in the mixture is increased, (a) Explain this occurrence. (b) Provide an explanation for the observation that the rate of the S]si2 reaction of ethyl chloride with potassium iodide in methanol and water decreases when the percentage of water in the mixture is increased. 

In contrast, neither electrophilic substituent constants nor constants provide a suitable basis for correlating the relative rates of solvolysis of l-(2-substituted 4-thiazolyl)ethyl chlorides, recalling similar poor correlations in several other heterocyclic systems. An alternative working model, based on a comparison of appropriately substituted pyridines and thiazoles, provides an adequate treatment of the substituent effects in these instances. ... 

The rate of solvolysis of l-(2-phenyl-5-thiazolyl)ethyl chloride is consistent with the substituent having an electrophilic substituent constant value of cTp = -0.34. This result is accounted for satisfactorily in terms of the coplanarity of the triazole and phenyl rings in this structure. ... 

Organoboranes react with ethyl 4-nitrobenzenesulphonyloxycarbamate under basic two-phase conditions in the presence of benzyltriethylammonium chloride or Aliquat to yield ethyl (V-alkylcarbamates [38]. The reaction probably proceeds via the initial formation of the nitrene, which reacts with the borane to form a B -N+ zwitterion. Subsequent rearrangement and solvolysis leads to the product. Aliquat is the better catalyst for the higher-molecular-weight boranes. 

Figure 48. Dependence of activation parameters for solvolysis of t-butyl chloride on mole fraction of water in ethyl alcohol + water mixtures at 298 K (Winstein and Fainberg, 1957), 4-184J = 1 cal.

Figure 51. Dependence of volume parameters for the solvolysis of benzyl chloride on mole fraction of alcohol in ethyl alcohol + water mixtures at 323 K (Mackinnon et al., 1970).

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