Reactivities, relative

About two years later, I did obtain a somewhat impure small sample from Professor Simonis, and about 0.1 gm from Professor Stock, which he shared with me from the very small piece he had. It is interesting to reflect that pure metallic beryllium became quite available only a few years later at something appreciably less than 10,000 a gram. From beryllium metal and from beryllium chloride we prepared the RBeX and R Be types, and obtained evidence to indicate that the following equilibrium is quite probable under certain conditions  

This apparently was the first reported case of a volatile organomagnesium compound. It is possible to ether-distill dimethylberyllium free of 

Over a period of years we prepared and examined an uncommonly broad array of organometallic compounds. Actually, studies were carried out on organometallic compounds which involved essentially all available metals and metalloids together with some of their derivatives (such as halides). While these studies were in progress, we wrote the following in our chapter (14) more than 30 years ago  

Our rules of reactivity were determined by various reactions. The functional groups used in evaluation in some studies were the carbonyl group, the nitrile group, and the double bond of some unsymmetrically substituted olefins. 

The term metalation was originally proposed by us about 35 years ago to denote the replacement of hydrogen bonded to carbon by metal to yield a true organometallic compound. We early observed in connection with studies of dibenzofuran types that metalation tended to yield ortho products. This direction to the ortho position, usually unmixed with para or other isomers, distinguishes the metalation reaction from the more familiar types of substitution, and makes possible the preparation of many compounds not readily available through other routes. This tendency to replace a nuclear 

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Compound Absolute reactivity (g Oj/g compound) Relative reactivity... 

For each type of component, its relative reactivity in ozone formation was taken into account which makes it possible to characterize by weighting the behavior of the overall motor fuel under the given experimental conditions. The overall reactivity is in fact governed by a limited number of substances ethylene, isobutene, butadiene, toluene, xylenes, formaldehyde, and acetaldehyde. The fuels of most interest for reducing ozone formation are those which contribute towards minimizing emissions of the above substances. 

Eurosuper gasoline Engine speed 1500 rpm Equivalence ratio 1,00 Sample point upstream of catalytic converter Relative reactivity factor Total teactivity 2.66 g O lg HC... 

Example of an analysis of exhaust gas by gas phase chromatography and j relative reactivity of effluents with respect to tropospheric ozone formation. I... 

Figure Cl. 1.3. Relative reactivity of transition-metal clusters with H2 (full curves, log scale) and tire promotion...

The use of dimethylformamide (b.p. 153°) as a solvent and diluent often increases the yield materially. The vigour of the exothermic reaction which occurs with a relatively reactive aryl hahde is moderated and, furthermore, the dimethylformamide is easily removed from the reaction product since it is water soluble. Aryl hahdes which are inert under the usual Ullmann conditions do not react in the presence of dimethylformamide. 

The operation of the nitronium ion in these media was later proved conclusively. "- The rates of nitration of 2-phenylethanesulphonate anion ([Aromatic] < c. 0-5 mol l i), toluene-(U-sulphonate anion, p-nitrophenol, A(-methyl-2,4-dinitroaniline and A(-methyl-iV,2,4-trinitro-aniline in aqueous solutions of nitric acid depend on the first power of the concentration of the aromatic. The dependence on acidity of the rate of 0-exchange between nitric acid and water was measured, " and formal first-order rate constants for oxygen exchange were defined by dividing the rates of exchange by the concentration of water. Comparison of these constants with the corresponding results for the reactions of the aromatic compounds yielded the scale of relative reactivities sho-wn in table 2.1. 

It may seem, at first sight, paradoxical that a competition reaction carried out under conditions in which the measured rate is independent of the concentration of the aromatic can tell us about the relative reactivities of two aromatics. Obviously, the measured rate has nothing to do with the rate of the product-determining step, and what is important in determining relative reactivities is the ratio of the values of ( 3.2.4) for two compounds. The criteria to be met for a correct application of the competitive method are well understood. ... 

As a means of determining relative reactivities, the competition method using nitronium tetrafluoroborate in sulpholan has been criticised as giving results which arise from incomplete mixing of the reagents before reaction is complete. The difficulty of using the competition method when the rate of reaction is similar to, or greater than,... 

The above definition implies that the reactivity of an aromatic compound depends upon the reaction which is used to measure it, for the rate of reaction of an aromatic compound relative to that for benzene varies from reaction to reaction (table 7.1). However, whilst a compoimd s reactivity can be given no unique value, different substitution reactions do generally set aromatic compoimds in the same sequence of relative reactivities. 

There are certain limitations to the usefulness of nitration in aqueous sulphuric acid. Because of the behaviour of the rate profile for benzene, comparisons should strictly be made below 68% sulphuric acid ( 2.5 fig. 2.5) rates relative to benzene vary in the range 68-80% sulphuric acid, and at the higher end of this range are not entirely measures of relative reactivity. For deactivated compounds this limitation is not very important, but for activated compounds it is linked with a fundamental limit to the significance of the concept of aromatic reactivity as already discussed ( 2.5), nitration in sulphuric acid cannot differentiate amongst compounds not less than about 38 times more reactive than benzene. At this point differentiation disappears because reactions occur at the encounter rate. 

The kinetics of the nitration of benzene, toluene and mesitylene in mixtures prepared from nitric acid and acetic anhydride have been studied by Hartshorn and Thompson. Under zeroth order conditions, the dependence of the rate of nitration of mesitylene on the stoichiometric concentrations of nitric acid, acetic acid and lithium nitrate were found to be as described in section 5.3.5. When the conditions were such that the rate depended upon the first power of the concentration of the aromatic substrate, the first order rate constant was found to vary with the stoichiometric concentration of nitric acid as shown on the graph below. An approximately third order dependence on this quantity was found with mesitylene and toluene, but with benzene, increasing the stoichiometric concentration of nitric acid caused a change to an approximately second order dependence. Relative reactivities, however, were found to be insensitive... 

The wM-diacetate 363 can be transformed into either enantiomer of the 4-substituted 2-cyclohexen-l-ol 364 via the enzymatic hydrolysis. By changing the relative reactivity of the allylic leaving groups (acetate and the more reactive carbonate), either enantiomer of 4-substituted cyclohexenyl acetate is accessible by choice. Then the enantioselective synthesis of (7 )- and (S)-5-substituted 1,3-cyclohexadienes 365 and 367 can be achieved. The Pd(II)-cat-alyzed acetoxylactonization of the diene acids affords the lactones 366 and 368 of different stereochemistry[310]. The tropane alkaloid skeletons 370 and 371 have been constructed based on this chemoselective Pd-catalyzed reactions of 6-benzyloxy-l,3-cycloheptadiene (369)[311]. 

As illustrated in Scheme 8.1, both 2-vinylpyrroles and 3-vinylpyiroles are potential precursors of 4,5,6,7-tetrahydroindolcs via Diels-Alder cyclizations. Vinylpyrroles are relatively reactive dienes. However, they are also rather sensitive compounds and this has tended to restrict their synthetic application. While l-methyl-2-vinylpyrrole gives a good yield of an indole with dimethyl acetylenedicarboxylate, ot-substitiients on the vinyl group result in direct electrophilic attack at C5 of the pyrrole ring. This has been attributed to the stenc restriction on access to the necessary cisoid conformation of the 2-vinyl substituent[l]. 

A more quantitative approach to the influence of the thiazole ring on the reactivity of a lateral functional chain was made in a recent study by Noyce and Fike (383), already discussed in Section 10.4. The first-order rates of solvolysis for three isomeric 1-thiazolylethyl chlorides were determined in 80% ethanol. The order of relative reactivity observed. 

TABLE III-37. COMPARISON OF THE RELATIVE REACTIVITIES (WITH RESPECT TO BENZENE) OF VARIOUS PYRIDINE SUBSTRATES towards PHENYL AND 2-THIAZOLYL RADICALS AT 70 TO... 

RELATIVE REACTIVITIES OF SOME HALO-AZA-ACTIVATED AROMATIC SUBSTRATES WITH NUCLEOPHILES ... 

The relative reactivity of alcohols increases m the order primary < secondary < tertiary... 

Relative reactivity is A (nucleophile)/A (methanol) for typical Sn2 reactions and is approximate Data pertain to methanol as the solvent... 

The relative reactivity of alkyl halides m 8 1 reactions is exactly the opposite of 8 2... 

Speculation about the stability of Ceo centered on the extent to which the aromaticity associated with its 20 benzene rings is degraded by their non planarity and the accompanying angle strain It is now clear that Ceo is a relatively reactive substance reacting with many substances toward which ben zene itself is inert Many of these reactions are char acterized by addition to buckminsterfullerene converting sp hybridized carbons to sp hybridized ones and reducing the overall strain... 

Relative reactivity toward sodium methoxide in methanol (50°C)... 

All of the reactions listed in Table 6.1 produce free radicals, so we are presented with a number of alternatives for initiating a polymerization reaction. Our next concern is in the fate of these radicals or, stated in terms of our interest in polymers, the efficiency with which these radicals initiate polymerization. Since these free radicals are relatively reactive species, there are a variety of... 

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