Reactions of the iso‐butyl radical during 1,1′‐azoisobutane pyrolysis

Quantitative analysis of the products formed in 1,1′‐azoisobutane pyrolyses in the temperature range of 553°–602°K has shown that the major reactions of the iso‐butyl radical areAnalysis of initial rate data gave log 10 k 4 /( k c ) 1/2 (cm −3/2 .mol 1/2 .sec −1/2 ) = 7.54±0.44 − (136.5 + 4.8) kJ/mol/2.303 RT , the Arrhenius parameters obtained being in good agreement with thermodynamic data for reaction (4). Measured values of k a /( k c ) 1/2 where k a is the rate constant of the reaction i C 4 H 9 + AIB → i C 4 H 10 +. AIB were consistent with published parameters determined by photolysis of 1,1′‐azoisobutane. Combination of photolysis and pyrolysis data gave log 10 k a /( k c ) 1/2 (cm 3/2 .mol −1/22 .sec −1/2 ) = 3.68 ± 0.15 − (27.2 ± 1.2) kJ/mol/2.303 RT . The crosscombination ratio for methyl and iso‐butyl radicals has been found to be 0.25, indicating that the geometric mean rule does not hold for methyl and iso‐butyl radicals.