The rate constants for the homolytic alkylation of protonated heteroaromatic bases (4-methyl- and 4-cyanopyridine, 4-methylquinoline, benzothiazole, and quinoxaline) were measured from 15 to 80 °C. A good agreement was obtained with two different kinetic models involving 5-hexenyl and n-heptyl radicals. The high values of the rate constants (a range of 105108 M-ls-1was obtained) explain the great synthetic interest of these reactions. On the contrary the homolytic alkylation of benzene derivatives has lower rate constants (102L mol-1 s-I), and shows a very poor synthetic interest. The observed failure of the reactivity-selectivity principle (RSP) was discussed in terms of polar effects and frontier orbitals theory. © 1977, American Chemical Society. All rights reserved.
Nucleophilic Character of the Alkyl Radicals. 16. Absolute Rate Constants and the Reactivity-Selectivity Relationship in the Homolytic Aromatic Alkylation
Citterio, Attilio;Minisci, Francesco;Porta, Ombretta;
1977-01-01
Abstract
The rate constants for the homolytic alkylation of protonated heteroaromatic bases (4-methyl- and 4-cyanopyridine, 4-methylquinoline, benzothiazole, and quinoxaline) were measured from 15 to 80 °C. A good agreement was obtained with two different kinetic models involving 5-hexenyl and n-heptyl radicals. The high values of the rate constants (a range of 105108 M-ls-1was obtained) explain the great synthetic interest of these reactions. On the contrary the homolytic alkylation of benzene derivatives has lower rate constants (102L mol-1 s-I), and shows a very poor synthetic interest. The observed failure of the reactivity-selectivity principle (RSP) was discussed in terms of polar effects and frontier orbitals theory. © 1977, American Chemical Society. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
