Relative reactivity at different ring-positions is postulated to be alterable by hydrogen bonding of an azine-nitrogen to the solvent or to the reagent (Section II, B, 3 and III,B). The effect of hydrogen bonding to nuclear substituents in transition states is reviewed in Sections I,D, 2,b, and II, E. It is postulated that hydrogen-bonded cyclic transition states such as 62 or the analogous one involving H0CH2CH20 will be found to increase relative reactivity adjacent to the azine-nitrogen in aprotic solvents cf. The oxidation of isopropylbenzene (cumene) is carried out on an industrial scale, with the ultimate products being acetone and phenol. The best preparative results from autoxidation are encountered when only one relatively reactive hydrogen is available for abstraction. This calculation provides the relative reactivity of chlorine atoms toward the primary and secondary hydrogens in butane. A statistical correction must be made to take account of the fact that the primary hydrogens outnumber the secondaiy ones by 3 2. 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. The relative reactivity k /k of the primary and secondaiy hydrogens is the sort of information that helps to characterize the details of the reaction process. For example, gas-phase chlorination of butane can lead to 1- or 2-chlorobutane. Īnother experiment of the competition type involves the comparison of the reactivity of different atoms in the same molecule. Nevertheless, it is important to recognize the very broad scope of electrophiUc aromatic substitution. Most of these electrophiles will not be treated in detail until Part B. Some indication of the relative reactivity of the electrophiles is given as well. Scheme 10.1 lists some of the specific electrophilic species that are capable of carrying out substitution for hydrogen. Usually, it is a substitution of some other group for hydrogen that is of interest, but this is not always the case. Ī wide variety of electrophilic species can effect aromatic substitution.
HYDROGENS REACTIVITY SERIES
The final conclusion is that the relative reactivities of isomeric positions in the pyrazolium series are determined essentially by inductive and hybridization effects. 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). 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. Addition to the 1-butene is less hindered than to the 2-butenes. The relative reactivities of the isomers are related to the relative stabiUty of the intermediate carbocation and are isobutylene 1 - butene > 2 - butenes. The addition requires an acidic reagent and the orientation of the addition is regioselective (Markovnikov). The rate of addition depends on the concentration of both the butylene and the reagent HZ.
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