Theodore Dibble - Intramolecular Hydrogen Bonding and Double H-Atom Transfer in Peroxy and Alkoxy Radicals from Isoprene, T.S. Dibble, J. Phys. Chem. A, 2004, 108, 2199

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      T.S. Dibble, J. Phys. Chem. A, 2004,  volume 108, 2199.


      Quantum mechanical calculations were used to determine the   structure and stability of second-generation peroxy and alkoxy   radicals formed in the atmospheric degradation of isoprene   (2-methyl-1,3-butadiene). Certain of these radicals exhibit a   novel hydrogen bonding motif, consisting of two intramolecular   hydrogen bonds. The hydrogen bonds are donated in series, with an   enol group donating a hydrogen bond to a −CH2OH group,   which donates in turn to the oxygen radical center. This hydrogen   bonding motif opens a new reaction pathway:  the simultaneous transfer of two H-atoms across the hydrogen   bonds with a barrier of only 5   kcal/mol in the alkoxy radicals, but 20   kcal/mol in the peroxy radicals. Rate constants for these   reactions were calculated, and the effects of tunneling on the   rate constant were examined. All species and reactions were   analyzed at the B3LYP/6-311G(2df,2p) level of theory; the   transition states for the double H-atom transfer reactions were   also studied using the MPW1K functional and the CBS-QB3 method.   Similar chemistry is possible for alkoxy and peroxy radicals   derived from other volatile organic compounds of atmospheric   interest.

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