Electrophilic Character of Oxygen Atoms

Abstract

The relative rates of reactions of oxygen atoms with a n~~r n b c r of olefins in the vapor phase deter~nined in previous nrorl; are s~ummarized and supplenlented by some additional results. The uncertainty in the values of the relative rate constants is no\\; believed to be reduced to only a few per cent. A n~~m b e r of simple correlations observed previously have been re-exa~~~inecl on the basis of the more complete and more accurate list of values available a t present. These correlations show a distinct electrophilic character of oxygen atoms in their reactions with olefins and their potential significance for the understanding of the finer details of these addition processes is discussed. INTRODUCTIONPossibilities of finding simple correlations between reaction rates and physical properties of the reactants have been extensively explored a t various times in the past wit11 the object of establishing the factors which contribute to chemical reactivity. Thus, for example, considerations of the lilcely potential energy changes when two molecules interact have suggested linear dependeilce of activation energies on such quantities as heats of reaction or singlet-triplet excitation energies (1-6). In the case of metathetical reactions such views have found little experimental support. Some additioil reactions, o n the other hand, a t least those involving a number of aromatic hydrocarbons (5, 6) and a somewhat restricted group of olefns (T), appear to show simple relations of this kind.Reactions of atoms v~ith serias of structurally related c o m p o u~~d s are particularly attractive for this type of investigation, especially if they can be studied under conditions where complications from solvei~t effects of variable magnitude can be eliminated. Solvent effects are of course absent in vapor phase reactions, but until very recentl~; there were essentially no rate clata for series of adclitioil reactions in the vapor phase. A11 exception to this represented the reactions of H-atom adclitio~ls to olefins, i~lvestigated by Robb and i\/Ielville (8). However, the work now in progress in this laboratory oil these reactions a t higher pressures and with the use of a clifferent technique (9) reveals some differences in the values of the rate constaiits from those obtaiiled by these authors. A discussion of the trends in reactivity in this reaction series has, therefore, to be delajwl until the current ivork is completecl.Although free atoins as a rule possess unpaired electroils and thus have free radical character, they nlay be expected to react in particular reactions as either electrophilic, nucleophilic, or radical reagents. ' he type of the reactant character exhibited mill be largely cleternlined by the relative values of the electron affinities ancl ioi~ization potentials of the atoins ancl their reaction partners.In the past several years extensive information on the vapor phase reactions of oxygen atoms with olefins has been accumulated in this laboratory. Both the mechanisn~ (10, 11) and the relative rates (1...

Temperature dependence of the rate constants of the reactions of oxygen atoms with 1‐pentene, 1‐hexene, cis‐2‐pentene, and trans‐2‐pentene

“…Biermann et al [17] obtained a value of (4.7 Ϯ 0.5) и 10 Ϫ12 cm 3 s Ϫ1 using a discharge flow system with photoionization detection. On the basis of these agreeing data, Cvetanović [7] recommended a value of (4.7 Ϯ 0.5) и 10 Ϫ12 cm 3 s Ϫ1 , which is the same as the slightly more precise value of the present study at 298 K. A relative room temperature rate constant for the reaction of O( 3 P) with 1-hexene has been obtained previously by Cvetanović from competing reactions [3]. The constant has been reevaluated to yield values of k ϭ 5.2 и 10 Ϫ12 cm 3 s Ϫ1 [8] and (4.60 Ϯ 0.08) и 10 Ϫ12 cm 3 s Ϫ1 [7].…”

A flash photolysis–resonance fluorescence kinetics study of ground‐state sulfur atoms. IV. Rate parameters for reaction of S(3P) with propene and 1‐butene

“…In the present study, the activation energy for reaction (3) was found to be the same as that for reaction (2). This result would have been expected on the basis of the explanation of the mode of attack of electrophilic group VIa atoms on olefins given by Cvetanovic [ 5 ] . The difference in the reactivity of S(3P) toward propene and 1-butene found in this work was small, being almost within the experimental error.…”

Importance of O(3P) atoms and OH radicals in hydrocarbon oxidation during the nonthermal plasma treatment of diesel exhaust inferred using relative‐rate methods

“…Third, they are readily available as high purity gas mixtures which can be handled conveniently by the experimental system. The literature data for k 1 19–31 and k 2 32–41 are discussed in the Appendix. For the present experimental conditions (453 K in 760 Torr of N 2 diluent) values of k 1 = 9.2 × 10 −13 , k 2 = 4.6 × 10 −12 , k 3 = 1.45 × 10 −12 42, and k 4 = 1.47 × 10 −11 cm 3 molecule −1 s −1 42 were used; we ascribe 20% uncertainty ranges for k 1 – k 4 .…”

“…In addition to the absolute rate data in Fig. A2, relative rate techniques have established that k 2 / k 9 = 0.23 at room temperature 39. …”