Isoprene (2-methyl-1,3-butadiene) is the single most important volatile carbon constributing to formation of ground-level ozone.  It constitutes about 40% by mass of  non-methane organic compound emissions to the atmosphere, and it is emitted almost exclusively by natural sources.    Chamber experiments over the years indicate that isoprene reacts with OH to form methylvinyl ketone 
(CH₃C(=O)CH=CH₂), methacrolein 
(O=CHC(CH₃)=CH₂), 3-methylfuran, and a number of other compounds.  The yields of these species are determined by the site of OH addition to isoprene and the fate of the alkoxy radicals; the latter topic is our focus.  The OH-initiated degradation of isoprene in the atmosphere is expected to produce four b-hydroxy alkoxy radicals (I-IV in the figure) and (E) and (Z) isomers of two d-hydroxy alkoxy radicals (V and VI).   Our studies indicate that the b-hydroxy alkoxy radicals decompose via C-C bond scission on a picosecond to nanosecond time scale.  Decomposition of the d-hydroxy alkoxy radicals would take at least milliseconds- far longer than the time required for the radicals to isomerize or react with O₂.  The isomerization reactions that abstract H-atoms from HOCH₂- groups are very fast, abstraction from the methyl group is not so fast as to rule out reaction with O₂.
 
        The figure above shows the possible C-C scission reactions of the alkoxy radicals from isoprene. 

Click on the thumbnail images for larger images of radical I  , 
 

or the Z isomer of radical V . 
 
 

Intramolecular hydrogen bonding, double H-atom transfer, and prompt chemistry of peroxy and alkoxy radicals from isoprene. See  overview.