Relative reactivities, qualitative

When this stereoelectronic requirement is combined with a calculation of the steric and angle strain imposed on the transition state, as determined by MM-type calculations, preferences for the exo versus endo modes of cyclization are predicted to be as summarized in Table 12.3. The observed results show the expected qualitative trend. The observed preferences for ring formation are 5 > 6, 6 > 7, and 8 > 7, in agreement with the calculated preferences. The relationship only holds for terminal double bonds. An additional alkyl substituent at either end of the double bond reduces the relative reactivity as a result of a steric effect. 

Chloroquinoline (401) reacts well with potassium fluoride in dimethylsulfone while its monocyclic analog 2-chloropyridine does not. Greater reactivity of derivatives of the bicyclic azine is evident also from the kinetic data (Table X, p. 336). 2-Chloroquinoline is alkoxylated by brief heating with methanolic methoxide or ethano-lic potassium hydroxide and is converted in very high yield into the thioether by trituration with thiocresol (20°, few hrs). It also reacts with active methylene carbanions (45-100% yield). The less reactive 3-halogen can be replaced under vigorous conditions (160°, aqueous ammonia-copper sulfate), as used for 3-bromoquino-line or its iV-oxide. 4-Chloroquinoline (406) is substituted by alcoholic hydrazine hydrate (80°, < 8 hr, 20% yield) and by methanolic methoxide (140°, < 3 hr, > 90% yield). This apparent reversal of the relative reactivity does not appear to be reliable in the face of the kinetic data (Tables X and XI, pp. 336 and 338) and the other qualitative comparisons presented here. 

The rate constant for p-scisskm is dependent on ring substituents. Rate constants for radicals X-Q.H. CCh are reported to increase in the series where X is / -Fi There is qualitative evidence that the relative rales for p-scission and addition are insensitive to solvent changes. For benzoyloxy radicals, similar relative reactivities are obtained from direct competition experiments10 as from studies on individual monomers when p-scission is used as a clock reaction.399,401... 

The relative reactivity of Friedel-Crafts catalysts has not been described in a quantitative way, but comparative studies using a series of benzyl halides has resulted in the qualitative groupings shown in Table 11.1. Proper choice of catalyst can minimize subsequent product equilibrations. 

The hydrogen consumption for the hydrogenation of WVGS 13421 and WVGS 13423, Table 6, qualitatively indicates the relative reactivity of the coals and their products. As discussed previously, prior to and after each experiment, the tetralin was analyzed chromatographically to determine the relative tetralin and... 

There is an obvious and urgent need for more systematic kinetic evidence and isotope effect studies, especially for the less strai tforward processes, and even purely qualitative observations of relative reactivities, solvent and spectator ligand effects, selectivity, and the nature of minor products would be of the greatest value. 

Tphe original objectives of this work were to determine how much the relative reactivity of two hydrocarbons toward alkylperoxy radicals, R02, depends on the substituent R—, and whether there are any important abnormalities in co-oxidations of hydrocarbons other than the retardation effect first described by Russell (30). Two papers by Russell and Williamson (31, 32) have since answered the first objective qualitatively, but their work is unsatisfactory quantitatively. The several papers by Howard, Ingold, and co-workers (20, 21, 23, 24, 29) which appeared since this manuscript was first prepared have culminated (24) in a new and excellent method for a quantitative treatment of the first objective. The present paper has therefore been modified to compare, experimentally and theoretically, the different methods of measuring relative reactivities of hydrocarbons in autoxidations. It shows that large deviations from linear rate relations are unusual in oxidations of mixtures of hydrocarbons. 

Finally, I would like to comment briefly on the effect of the metal on ligand reactivity. In a number of instances chelate rings in the trisacetylacetonates of rhodium(III), cobalt(III), and chromium(III) undergo electrophilic substitutions at different rates. The relative reactivity of these complexes is chromium > cobalt rhodium. Thus far our data are only qualitative. 

Obviously, since the gas-carbon reactions have different activation energies and orders of reaction, the relative rates of these reactions will be a function of the temperature and pressure selected for the correlation. Unfortunately, the authors can find no reactivity data for all four of the gas-carbon reactions using the same carbon. Furthermore, data for even two of the gas-carbon reactions on the same carbon are limited. The available data will be taken and extrapolated, where necessary, to give at least a qualitative idea of relative rates of the gas-carbon reactions at 800° and 0.1 atm. gas pressure. Extrapolation of these relative reactivities to other temperatures and pressures by the reader will require the assumption of activation energies and orders of reaction. 

Consequently, with the present knowledge of reductive dehalogenation reactions of Cr and C2-compounds, and considering the quality of the various molecular descriptors, only qualitative, or at most semiquantitative, predictions of the relative reactivities of a confined set of structurally related compounds in a given system are possible. Nevertheless, evaluation of such relative reactivities in different systems may provide important insights into such reactions, which will be demonstrated by the following two examples. These two examples will, however, also illustrate the... 

Although nonproductive binding is not a mechanism for increasing KM, it is appropriately discussed here since it gives rise to effects that are qualitatively similar to those of strain and induced fit. This theory was originally invoked to account for specificity in the relative reactivities of larger, specific substrates compared with smaller, nonspecific substrates. It is assumed that as well as the productive binding mode at the active site, there are alternative, nonproductive modes in which the smaller substrates may bind and not react. 

Using a competition method, Lillya et a/.15,16 obtained relative reactivities for a series of substituted diene-tricarbonyliron compounds toward the methyloxocarbonium tetrachloroaluminate ion pair in di-chloromethane. The results are qualitatively summarized in Scheme 4. 

Equation (39) therefore remains unchanged since the term in a cancels. An exactly similar argument holds for nucleophilic substitution we therefore conclude that (1) the relative reactivities of different hydrocarbons, and the relative reactivities of different positions in the same hydrocarbon, should be the same for substitution by reagents of all kinds, and (2) there should be in each case a linear relation between log k and The first relationship holds qualitatively in all cases except where steric effects are involved thus naphthalene is more reactive than benzene to reagents of all three types (e.g. nitric acid, phenyl radicals, sodamide), and in each case the a-position in naphthalene is more reactive than the / the corresponding free valence numbers are ... 

Parr and Pearson 1301 defined a parameter 17, which they called "absolute hardness" (17 V4[IP-EA]), and calculated 17 for a variety of neutral and ionic Lewis acids and bases possessing from one to four atoms. These authors showed that the qualitative predictions of the HSAB model regarding the relative reactivities of these species toward one another may be obtained using the results from simple calculations of stabilization energies using 17 and electronegativity values. 

Sol-gel preparation offers excellent control of mixing because of its ability to alter relative precursor reactivity. Qualitatively, we expect good mixing when the two precursors have similar reactivities and poor mixing when they do not. As pointed out in Section 2.1.4.2.A, both hydrolysis and condensation are nucleophilic displacement reactions. Effective strategies in matching precursor reactivity thus include ... 

Electrophilicity — (1) The property of being - electrophilic (see -> electrophile). (2) The relative reactivity of an electrophilic reagent. (It is also sometimes referred to as electrophilic power ) Qualitatively, the concept is related to Lewis acidity (- acid-base theories). However, whereas Lewis acidity is measured by relative - equilibrium constants, electrophilicity is measured by relative -> rate constants for reactions of different electrophilic... 

Consequent upon the orbitals preferred for the unpaired electron, a high spin population occurs at C-4 in each of 1,52, and 53. These are the anion-radicals found to exhibit the least persistence.35 Relative reactivities of the anion-radicals have been estimated by a cyclic voltammetric method as 1 > 1,3,5-triazine anion-radical > 52 > 53 > 22 > 54, which corresponds with qualitative observations on persistence and accords very closely with the ranking order of maximum spin populations at carbon.119 120 Dimerization of the radicals at positions of high spin population at carbon is proved for 1 and 52, although the mechanism is by no means clear for 52 and other modes of reaction can also occur, e.g., proton abstraction from solvent or adventitious water.30,35,121-127... 

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