Relative reactivity data

Giese and Feix65 examined the temperature dependence of the relative reactivity of fumarodinitrilc and methyl a-chloroacrylatc towards a scries of alkyl radicals (Scheme 1.6). The temperature dependence was such that they predicted that the order of reactivity of the radicals would be reversed for temperatures above 280 K (the isosclcctivc temperature - Figure 1.3). This finding clearly indicates the need for care when comparing relative reactivity data.66... 

The reactions of cyanoisopropyl radicals with monomers have been widely studied. Methods used include time resolved EPR spectroscopy,352 radical trappingj53 355 and oligomer00 356 and polymer end group determination. 1 Absolute341 and relative reactivity data obtained using the various methods (Table 3.6) are in broad general agreement. 

Absolute rate constants for addition reactions of cyanoalkyl radicals are significantly lower than for unsubstituted alkyl radicals falling in the range 103-104 M V1.341 The relative reactivity data demonstrate that they possess some electrophilic character. The more electron-rich VAc is very much less reactive than the electron-deficient AN or MA. The relative reactivity of styrene and acrylonitrile towards cyanoisopropyl radicals would seem to show a remarkable temperature dependence that must, from the data shown (Table 3.6), be attributed to a variation in the reactivity of acrylonitrile with temperature and/or other conditions. 

Hindered lithium dialkylamides can generate aryl-substituted carbenes from benzyl halides.162 Reaction of a,a-dichlorotoluene or a,a-dibromotoluene with potassium r-butoxide in the presence of 18-crown-6 generates the corresponding a-halophenylcarbene.163 The relative reactivity data for carbenes generated under these latter conditions suggest that they are free. The potassium cation would be expected to be strongly solvated by the crown ether and it is evidently not involved in the carbene-generating step. 

Routes to Relative Reactivity Data Relative reactivity relationships describe the ratio of products between two glycosyl donors for an acceptor. Ley first constructed such relationships for fully protected mannoside and rhamnoside donors to rationalize the results of his one-pot syntheses employing cyclic diketals.16... 

Scheme 11.19 One-pot syntheses of tri- and tetrasaccharides using relative reactivity data.

The relative reactivity data for some pentene derivatives are given in Table 4.2. 

Acyl chlorides were also tested in acylations promoted by B(OTf)3.231 Acylation of benzene and toluene in competitive reactions (molar ratio = 5 1) with acetyl chloride shows high para selectivity (92-95% with 2.5-7% of meta, kT/kB — 31-73), whereas the para isomer is formed only with 72-75% selectivity (8-10% of meta, k lkK = 78) in benzoylation with benzoyl chloride. Acetylation appears not to be affected by significant isomerization as indicated by isomer distributions and relative reactivity data. 

In another study, tertiary secondary primary relative reactivity data (TSP selectivity) for the deprotonation reactions of alkylbenzene radical cations [ 153] showed that with both intra- and intermolecular TSP selectivity the order S > T > P is usually observed, suggesting that the combination of steric and stereoelectronic effects makes an /Pr group less reactive than Et, but still more reactive than Me. 

From the relative reactivity data, shown in Table 2, which describes the thermal decomposition of biscyclopropanoyl peroxide in a series of substituted benzenes, Shono and Nishiguchi have concluded that the cyclopropyl radical more closely resembles the... 

Qualitative relative reactivity data indicate that metal alkyls with alkyl groups that form the best radicals are the most reactive, suggesting a free-radical mechanism . These reactions give the 1,2-addition products as well as the 1,4-keteniminate isomers. 

A//jransfer data for n-hcxyl tosylate and several nucleophilic anions are given in Table 4.P1.21. In Table 4.P2.21, the activation parameters for Sjv2 displacement reactions with -hexyl tosylate are given. Use these data to construct a potential energy comparison for each of the nucleophiles. Use these diagrams to interpret the relative reactivity data given in Table 4.P3.21. Discuss the following aspects of the data. 

Relative reactivity data for nitration must be treated with special caution because of the possibility of encounter control. An example of this can be seen in Part A of Table 9.7, where no difference in reactivity between mesitylene and xylene is found in H2SO4-HNO3 nitration, whereas in HNO3-CH3NO2 the rates differ by a factor of more than 2. Encounter-control prevails in the former case. In general, nitration is a relatively unselective reaction with toluene being about 50-60, as shown in... 

Much of the relative reactivity data on 1,3-DPCA reactions has been tabulated and discussed in reviews by R. Huisgen, a pioneer researcher in the field.Some representative data are presented in Table 10.3. The dipolarophiles are shown in decreasing order of electrophilicity. The data from these monosubstituted dipolarophiles should be relatively free of steric influences on reactivity. Note that for phenyl azide and benzonitrile oxide, reactivity is at a minimum for unfunctionalized alkenes and is increased by both donor and acceptor substituents. 

Absolute and relative reactivity data obtained using the various metliods (Table 3.6) are in broad general agreement. 

Within this set, the reactivity of isobutene was assigned as 1.0, and the reactivities of the other alkenes toward CXY were measured relative to isobutene. Data of this sort are illustrated for CF2, CCI2, and CBr2 in Table 1. [9-12] (Avery large collection of relative reactivity data for many carbenes appears in ref 11). 

Relative reactivity data show that the order of reactivity for alkyl halides is tert>sec>pri>methyl This order can be accommodated by a carbonium-ion mechanism or by a process involving a complex of the halide and the catalyst. In either case, the heterolysis of the C-halide bond will be facilitated by additional alkyl groups. 

A variety of kinetic data permit the assignment of relative reactivities toward solvolysis of a series of systems related to the norbornane skeleton. Offer a general discussion of the structural effects that are responsible for the observed relative reactivity data. 

Selectivity and relative reactivity data for nitration under a variety of conditions... 

The reactivity of alkenes toward mercuration varies over a considerable range and is governed by a combination of steric and electronic factors.Terminal double bonds are more reactive than internal ones. Disubstituted terminal olefins, however, are more reactive than monosubstituted cases, as would be expected for electrophilic attack. The differences in relative reactivities are large enough that selectivity can be achieved in certain dienes. Relative reactivity data for some pentene derivatives are given in Table 4.2. 

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