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Double . . . . H-atom Transfer, and of Alkoxy Radicals

Intramolecular . . . Hydrogen Bonding,. Double . . . . H-atom Transfer, and of Alkoxy Radicals from Isoprene. Prompt Chemistry. T. S. Dibble Chemistry Department, SUNY-ESF. OH O 2 , NO. (“Vacuum cleaner of the atmosphere”).

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Double . . . . H-atom Transfer, and of Alkoxy Radicals

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  1. Intramolecular. . . Hydrogen Bonding, Double . . ..H-atom Transfer, and of Alkoxy Radicals from Isoprene Prompt Chemistry T. S. Dibble Chemistry Department, SUNY-ESF

  2. OH O2, NO (“Vacuum cleaner of the atmosphere”) Importance of Isoprene in the Atmosphere (Oxidizes SO2 to sulfuric acid) HOOH OH O2 O3 (Health Hazard) Global Organic compound emissions CH4 530 Tg/year Isoprene 500 Tg/year Other 650 Tg/year

  3. Chemistry Forming Second Generation Radicals (Paulson and Seinfeld, 1992) VIIO VIIOO VII Note many branching pathways are not shown above!!

  4. But double hydrogen bonding of (Z) isomer inhibits decomposition, unlike single H-bond (Dibble 1999) in first generation alkoxy radicals. Second Generation Alkoxy Radicals Expected to Decompose (Paulson and Seinfeld, 1992) (Dibble, 2002)

  5. (4) 0 Kcal/mole -19 Kcal/mole Unexpected Chemistry Unexpected Chemistry Unexpected Chemistry Unexpected Chemistry Double H-atom Transfer

  6. 3 3 4 4 1 1 (Z) VII’OH (34, 4 1) (Z) VIIO(14, 4 3) Nomenclature We identify oxygen atoms by the number (in isoprene) of the carbon atom to which it is bound. The O atom acting as a hydrogen bond donor is to the left of an arrow, the acceptor is to the right.

  7. 3 4 1 Multiple Hydrogen bonding Arrangements (zero, one, or two hydrogen bonds) (Z) VII’OH (34, 4 1) (Z)-VII’OH (31) (Z)-VII’OH (43,31) (Z)-VII’OH (41) (Z)-VII’OH (none) (Z)-VII’OH (43)

  8. Relative Energies, H-atom transfer, and H-bonding 10 5 (Z)-VIIO (1  3)’ 0 (Z)-VIIO (1  4,4 3) -5 Kcal/mol -10 (Z)-VII’OH (none) (Z)-VII’OH (4  3) (Z)-VII’OH (3  4) -15 (Z)-VII’OH (3  1) (Z)-VII’OH (4 1) -20 (Z)-VII’OH (4  3,3 1) (Z)-VII’OH (3  4,4 1)

  9. Part of the Potential Energy Profile Thermal Decomposition of VII’OH is slow... 10 5 (Z)-VIIO (1  3)’ 0 (Z)-VIIO (1  4,4 3) -5 Kcal/mol -10 (Z)-VII’OH (none) (Z)-VII’OH (4  3) (Z)-VII’OH (3  4) -15 (Z)-VII’OH (3  1) (Z)-VII’OH (4 1) -20 (Z)-VII’OH (4  3,3 1) (Z)-VII’OH (3  4,4 1)

  10. … But Prompt Decomposition of VII’OH is Extensive!

  11. Consequences for Atmospheric Chemistry? Decomposition of VIIO same as Prompt Decomposition of VII’OH! But quenched VII’OH results in different chemistry

  12. Theodore S. Dibble tsdibble@syr.edu Chemistry Department State University of New York - Environmental Science and Forestry Syracuse, NY 13210 http://www.esf.edu/chemistry/faculty/dibble.htm J. Phys. Chem A,(2004)108, 2199 and 2208. Acknowledgements NSF-Atmospheric Sciences NCSA - University of Kentucky Wei Deng, Katherine Kitney, Lei Zhang

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