Some reactions of the isopropyl radical

Abstract

The decomposition of ethane sensitized by isopropgl radicals was studied in the tempera-The rate of formation of n-butane, isopentane, and 2,S-dimethyl-t,iire range of 496-548°K. butane were nieasrued. The expression kI/PZ1'* was found to be log kl/kg"2(dm3'*/n~ol"2 . see1!*) = (3.2 f 0.4) -(54 f 3 kJ/mol)/2.3RTwhere k , and k 2 are rate constants ofThe decomposition of propylene sensitized by isopropgl radicals was studied between 494 The :end 580'K by determination of the initial rates of formation of the main products. ratio of k13/k2"2 was evaliiated to be Ii)g kl3/k."!2(diii3'*/mnIl~* . sec1i2) = (1.9 f 0.7) -(32 f 7 kJ/mol)/P.3RTwhere k , , is the r:tte constant forThe isoinerizat ion of the isopropyl radical was investigated by st tidying the decomposition The decomposition of the iso-C3H7 radical into C2H, and CHI was followed On the basis of the experiment.al data, obtained Of azoisopropane. I)? measuring the rate of formation of C,H+ irr the range of 538-666' K, k 1~/ k 2~1~ was found: log k I 5 / k 2 l 2 ( m o l~~~/ d n i 3 * . sec1:2) = (9.3 f 0.8) -(152 f 9 kJ/mol)/2.3RT where k 1 5 is the rate constant of i I .i) iso-CaH; --t [n-C:,Hi] ---* CH3

β-Bond Scission and the Yields of H and CH3 in the Decomposition of Isobutyl Radicals

“…The isobutyl case is illustrated in Scheme where both reactions R1b and R1c lead to isobutene and H. While we will argue later that the 1,2 H shift in isobutyl is unimportant, it cannot be distinguished from direct C–H scission based on the end products. Studies in the literature of C–H bond scission ,− and 1,2 H shifts ,,− have yielded conflicting results, and this literature will be briefly reviewed in the discussion section and compared to our results. − ,− …”

“…In a series of papers from the 1960s on strategically deuterated, isopropyl and isobutyl radicals, Jackson and McNesby − set upper limits on the amount of 1,2 H-shifts and C–H β-scission at (472 to 813) K of 7% for isopropyl and 1% for isobutyl and argued that these upper limits were lower than other literature values because their experiments were free from nonthermal photochemistry . Multiple other researchers claimed significant 1,2 H-shift branching ratios for decades afterward. − ,, These claims were usually based, however, on the detection of compounds that could easily be produced from side chemistry, including methane and ethene. , …”

Thermal decomposition of azoisopropane. II. Secondary decomposition processes

“…Under the analytical conditions reported by Szirovicza and Marta [51, DMB and 2-methylpentane can not be separated. In the presence of propylene, however, the two substances are formed in comparable amounts, which were measured jointly in [5]. It follows from the rate constant expression that with the increase of the quantity of DMB values lower than the probable ones are obtained for the Arrhenius parameters of kls.…”

Thermal decomposition of 2,2‐propane‐d2. CH3CDCH3 radical isomerization

“…Analyzing the kinetic results available for the isomerization of isopropyl radicals it can be concluded that with two exceptions the rate constant data are within a factor of about 10. The results originated from the pyrolysis of azoisopropane are higher by more than two orders of magnitude than the lowest rate constant [8]. This discrepancy can be explained by the assumption that azoisopropane had some n -C3H7 contamination (for instance, nX3H7-N = N -~s o -C~H~, which is difficult to detect in excess of azoisopropane).…”