Relative reactivities of hydrogens

The scrambling of 12% deuterium to the 2-position is consistent with a relative reactivity of hydrogen at the 1-position to hydrogen at the 2-position of (very roughly) 3 1 toward hydrogen abstraction. Further evidence for the formation of 2-tetralyl radical comes from the observation of 1-methylindan from the thermal rearrangement of tetralin. Work in our laboratory has shown that 1-methylindan results from the 1,2-phenyl migration of 2-tetralyl radical and does not occur via 1-tetralyl... 

Method B. Another, similar system we have used to measure the relative reactivities of hydrogen atoms involves the use of tritiated thiol. In this case, the rate of incorporation of tritium into the QH is measured (10,22). This system is shown below ... 

SCHEME 6, Relative reactivities of hydrogen atoms in 2-methylheptane towards Cl at 20 °C ... 

The rate of addition depends on the concentration of both the butylene and the reagent HZ. The addition requires an acidic reagent and the orientation of the addition is regioselective (Markovnikov). The relative reactivities of the isomers are related to the relative stabiUty of the intermediate carbocation and are isobutylene 1 — butene > 2 — butenes. Addition to the 1-butene is less hindered than to the 2-butenes. For hydrogen bromide addition, the preferred orientation of the addition can be altered from Markovnikov to anti-Markovnikov by the presence of peroxides involving a free-radical mechanism. 

The hydrogen-deuterium exchange rates for 1,2-dimethylpyrazolium cation (protons 3 and 5 exchange faster than proton 4 Section 4.04.2.1.7(iii)) have been examined theoretically within the framework of the CNDO/2 approximation (73T3469). The final conclusion is that the relative reactivities of isomeric positions in the pyrazolium series are determined essentially by inductive and hybridization effects. 

A wide variety of electrophilic species can effect aromatic substitution. Usually, it is a substitution of some other group for hydrogen that is of interest, but this is not always the case. Scheme 10.1 lists some of the specific electrophilic species that are capable of carrying out substitution for hydrogen. Some indication of the relative reactivity of the electrophiles is given as well. Most of these electrophiles will not be treated in detail until Part B. Nevertheless, it is important to recognize the very broad scope of electrophiUc aromatic substitution. 

The value of k /k can be determined by measuring the ratio of the products 1-chlorobutane 2-chlorobutane during the course of the reaction. A statistical correction must be made to take account of the fact that the primary hydrogens outnumber the secondaiy ones by 3 2. This calculation provides the relative reactivity of chlorine atoms toward the primary and secondary hydrogens in butane ... 

Problem 10.4 Taking the relative reactivities of 1°, 2°, and 3° hydrogen atoms into account, what product(s) would you expect to obtain from monochlorination of 2-methylbutane What would the approximate percentage of each product be (Don t forget to take into account the number of each sort of hydrogen.)... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Figure 1.9 Relative reactivity per hydrogen atom of indicated site towards t-...

Only limited success was achieved in determining the relative reactivity of primary, secondary, and tertiary carbon-hydrogen bonds to sulphonyl nitrenes 8>. Insertion of p-toluenesulphonyl nitrene into 2-methylbutane gave a mixture of products which could not be completely resolved. The ratio of (primary) (secondary + tertiary) = [38 + 39 40 + 41] was 1.53, compared to a ratio of 5.6 for carbethoxynitrene58>, indicating the lowered selectivity of the sulphonyl nitrene relative to the carbethoxynitrene, as might be expected from the possible resonance stabilization of the latter species. 

The yield of conjugation using the Mannich reaction is dependent on the reactivity of active hydrogens within the hapten molecule. It is often difficult to predict the relative reactivity of any given compound in this reaction. Thus, trial and error may be necessary to determine the suitability of the Mannich procedure. 

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... 

Kurahashi, T. Mizutani, T. Yoshida, J., Effect of intramolecular hydrogen-bonding network on the relative reactivities of carbohydrate OH groups. J. Chem. Soc. Perkin Trans. 1 1999, 465-473. 

The competihve hydrogenation of alkyl-substituted arenes was also performed with lr(0) nanoparhcles [49]. Using toluene as a standard substrate, several toluene/ benzene and toluene/monoalkylbenzene hydrogenation experiments were conducted in order to determine the selectivity constants of the transition-metal nanoparticles. These selechvity constants can be used to predict the relative reactivity of any other couple of monoalkylbenzenes. A series of initial reaction... 

The relative performances of the two autoclaves were compared by the use of ratios. Three ratios were derived utilising (a) the unconverted phenanthrene, denoted by P (b) the amounts of the various hydro-derivatives of phenanthrene multiplied by the relative number of hydrogens added, eg % tetrahydrophenanthrene 4, denoted by HP (c) the total content of hydrocracked compounds, denoted by C. These ratios would indicate the reactivity of the autoclaves and their relative abilities towards hydrogenation and hydrocracking. 

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