Factors Affecting the Rates of Addition of Free Radicals to AlkenesDetermination of Absolute Rate Coefficients Using the Persistent Aminoxyl Method
作者:Athelstan L. J. Beckwith、James S. Poole
DOI:10.1021/ja025730g
日期:2002.8.1
The rate of coupling of alkyl radicals with the persistent aminoxyl radical 1,1,3,3-tetramethylisoindolin-N-oxyl (1) has been used as a kinetic probe to determine absolute rate coefficients for the addition of alkyl radicals to methyl acrylate. The results are discussed in terms of the role of the structure and functionalization of the attacking radical on the rates of addition, particularly as they
Absolute rate constants for the reaction of triethylsilyl radicals with organic halides
作者:C. Chatgilialoglu、K. U. Ingold、J. C. Scaiano
DOI:10.1021/ja00383a022
日期:1982.9
Formation and homolysis of organonickel(III) complexes
作者:Douglas G. Kelley、Adam Marchaj、Andreja Bakac、James H. Espenson
DOI:10.1021/ja00020a020
日期:1991.9
The reactions of Ni(1,4,8,11-tetraazacyclotetradecane)2+ with alkyl radicals were studied. Data were collected for the R,R,S,S (or beta) and R,R,R,R (or alpha) isomers. The reactions form sigma-bonded organometallic cations, as in the equation NiL2+ + R. + H2O reversible RNiL(H2O)2+. The values of the rate constants for the forward (colligation) and reverse (homolysis) reactions were measured separately by laser flash photolysis techniques with a kinetic probe. The values of k(col) lie in the order CH3 >> primary >> secondary, and just the reverse order applies to k(hom). Thus the equilibrium constants for formation of RNiL(H2O)2+, given by k(col)/k(hom), are most favorable for methyl and least favorable for secondary alkyls. These nickel-alkyl bonds are much weaker than those in corresponding cobalt and chromium complexes. For that reason, values of k(col) vary widely with the nature of R.. Values of k(col) are considerably higher for alpha-Ni(cyclam)2+ than for the beta-isomer, and the reverse order applies to k(hom). Also, the alpha-isomer has the highest equilibrium constant for the formation equilibrium. The kinetic and thermodynamic trends can be rationalized by structural effects.
On the Removal of Metallic Mirrors by Free Radicals
作者:Francis Owen Rice、Joan Tweedell
DOI:10.1002/bbpc.19870911003
日期:1987.10
AbstractLarge Radicals can be formed by passing chlorinated organic compounds at pressures of a few ram., through a furnace containing a pellet of sodium and heated to 350–400°C. It seems to us that the only radicals that will remove metallic mirrors (of tellurium or antimony, etc., previously deposited beyond the furnace) are those that can decompose into methyl or ethyl radicals plus an unsaturated molecule, without undergoing any transmigration of atoms.
Reactions of Atomic Oxygen (3P) with Selected Alkanes
Rate constants for the reactions of atomic oxygen (P-3) With selected alkanes (C-2-C-6 Straight chain alkanes, C-C6H12, neo-C5H12, and i-C4H10) have been determined directly by a laser photolysis-shock tube-atomic resonance absorption method at high temperatures (850-1250 K). For n-C6H14 and c-C6H12, rate constants have been also determined at lower temperatures (296-400 K) by a laser photolysis-vacuum ultraviolet laser-induced fluorescence method. Present results agree with the TST calculation by Cohen and Westberg [Int. J. Chem. Kinet. 1986, 18, 99] within experimental error limits except for O + c-C6H12 and O + neo-C5H12. The group additivity of the rate constants for different C-H bonds (primary, secondary, and tertiary) is examined and neo-C5H12 and c-C6H12 are found to be good representatives of primary and secondary C-H bonds, respectively, for C-4 and larger alkanes. A trial is made to investigate the J dependence of reactivity of atomic oxygen (P-3(J)) With c-C6H12 to examine the adiabatic correlation of reactants and products. No evidence for such J dependence can be observed due to the rapid relaxation among the spin-orbit components. Rate constants for the intratriplet relaxation processes are evaluated for He as a collision partner.