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

2. OH O 2 OH O 2, NO O3O3 HOOH Global Organic compound emissions CH 4 530 Tg/year Isoprene 500 Tg/year Other 650 Tg/year Importance of Isoprene in the Atmosphere (Oxidizes SO 2 to sulfuric acid) (Health Hazard) (“Vacuum cleaner of the atmosphere”)

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

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

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

6. 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. (Z) VIIO(1  4, 4  3) 1 3 4 (Z) VII’OH (3  4, 4  1) 1 3 4

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

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

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

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 Acknowledgements NSF-Atmospheric Sciences NCSA - University of Kentucky Wei Deng, Katherine Kitney, Lei Zhang J. Phys. Chem A, (2004) 108, 2199 and 2208.