Radical Attack on Alkanes and Related Compounds

The subscripts p, s, t, refer to attack at primary, secondary, and tmtiary C—H bonds, respectively. Values of A (per C—H bond) and are available those for 

Suitable sources of HOa, RO2, and RCX 2 radicals are still lacking, and then-need is increasingly pressing. From their study of the photo-oxidation of 2,3-dimethylbutane, Alcock and Milegive kaob = 1.6 x 10 and ktt, = 

5 kJ mo - for HOa attack at tertiary C—H bonds in alkanes. On the assumption of equal A factors (per C—H bond), then . = 52.6 uid p = 62.5 kJmol- for attack at secondary and primary positions, respectively. These are the first Arrhenius parameters for HOa + alkane reactions determined from experimental studies at different temperatures. 

From Alcock and Mile s results, ktob = kab within experimental error, and in the absence of values of A Db at other temperatures the HOa + alkane parameters are recommended for ROa + alkane. Arising from the modulation spectroscopy experiments (Method XII and Section 5), Parkes gives k(MeOa + i-C Hio) 24 dm mol- s at 298 K, so that with /t, = 4.9 x 10 then , 36 kJ mol-,  

Lloyd has reviewed HO2 reactions to the end of 1973 Table 9 lists rate constants determined in the interim. The position on the voy important reaction H02 + CO has hardened considerably. There is now no doubt that Westenberg and de Haas value of 39 1.0 x lO at 298 K is at least 6 ord s of magnitude too high. Vardanyan, Sachyan, and Nalbandyan have re-examined reaction (39), 

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