Intramolecular Hydrogen Bonding

Slide1 : Double . . . .H-atom Transfer, and of Alkoxy Radicals from Isoprene Prompt Chemistry Intramolecular. . . Hydrogen Bonding, T. S. Dibble Chemistry Department, SUNY-ESF

Slide2 : OH O2 O3 HOOH Global Organic compound emissions CH4 530 Tg/year Isoprene 500 Tg/year Other 650 Tg/year Importance of Isoprene in the Atmosphere (Oxidizes SO2 to sulfuric acid) (Health Hazard)

Slide3 : Chemistry Forming Second Generation Radicals (Paulson and Seinfeld, 1992) Note many branching pathways are not shown above!! VIIO VIIOO VII

Slide4 : Second Generation Alkoxy Radicals Expected to Decompose (Paulson and Seinfeld, 1992) (Dibble, 2002)

Slide5 : Unexpected Chemistry Double H-atom Transfer Unexpected Chemistry Unexpected Chemistry Unexpected Chemistry

Slide6 : 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.

Slide7 : 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)

Slide8 : 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

Slide9 : 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...

Slide10 : … But Prompt Decomposition of VII’OH is Extensive!

Slide11 : Consequences for Atmospheric Chemistry? Decomposition of VIIO same as Prompt Decomposition of VII’OH! But quenched VII’OH results in different chemistry

Slide12 : 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.