Isobutane radical attack

Reaction of CF with benzene generates the 7-fluoronorcaradien-7-ly radical (39), which abstracts hydrogen (from added isobutane) and opens to 7-fluorocyclohepta-triene (40). Cycloheptatriene (10) is trapped as tropylium fluoroborate (41) by the addition of BF3 (Eq. 21)P An additional product of CF + benzene is fluorobenzene (42), in which labeling studies demonstrate that the attacking carbon contains the fluorine in 42. The interesting transfer of CH in Eq. 28 is proposed to account for the formation of 42. " ... 

Russell, G. A. Solvent effects in the reactions of free radicals and atoms. II. Effects of solvents on the position of attack of chlorine atoms upon 2,3-dimethylbutane, isobutane and 2-deuterio-2-methyl-propane. J. Amer. chem. Soc. 80, 4987 (1958). 

The second chain is again initiated by H or CH3 but goes through the isobutyl radical, —CH2—CH(CH3)2, which can only stabilize itself in a simple way by splitting off CH3 (reactions 5, 8, and 6 ). Its stoichiometry is represented by isobutane —> CH4 + C3TI6. From the preponderance of H2 and C4H8 as products of the reaction it would seem that the principal mode of attack of H or CH3 on isobutane is to abstract the tertiary H atom and produce the -butyl radical (reactions 5, 8). ... 

An insertion-type mechanism for the S( Z)) atom reaction is further supported by the indiscriminative nature of the attack on the various paraffinic C—H bonds. For the propane and isobutane molecules it was found that the two possible isomeric mercaptans were formed in a statistical ratio, i.e., n-PrSH/iso-PrSH 5 3.0, and iso-BuSH/f-BuSH iii 9.0. From methylene chemistry it is well known that singlet CH2 in its insertion reactions may be completely indiscriminative, but the abstractive attack of free radicals upon C—H bonds is known to be very sensitive to bond order and strongly increases in the sequence 0° < 1° < 2° < 3°. Insertive interactions with C—H bonds have also been postulated for singlet and triplet carbon atoms, NH, C2O radicals, and recently for the reactions of 0( Z)) atoms with alkanes. ... 

Manganese is ineffective as a catalyst under the conditions used in high-con-centration cobalt cases [68]. It does not appear to take part in an electron transfer mechanism such as eq. (25). It functions mainly via a free radical pathway [48, 69]. The high concentration cobalt-ion catalyst system also exhibits pronounced steric influences. Hydrogen atoms which are readily abstractable in conventional oxidations are bypassed in favor of less reactive hydrogenswhich are not sterically hindered. For example, isobutane is less readily attacked than -butane. 

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