Exploration of Energetic Pathways of Vinyl Hydroperoxides in the Troposphere: Applied to Ozonolysis of Single Pi Bond Alkenes and Isoprene

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1 Exploration of Energetic Pathways of Vinyl Hydroperoxides in the Troposphere: Applied to Ozonolysis of Single Pi Bond Alkenes and Isoprene Lina Luu and Alexander Weberg

2 Hydroxyl Radical in the Atmosphere Most important oxidant in troposphere Plays key role in initiating oxidation reactions Responsible for removing trace gases Greenhouse gases Carbon monoxide Most often produced through photolysis of ozone in the presence of water vapor

3 Alkene Ozonolysis Mechanism to Hydroxyl Radical Dark Hydroxyl Radical Formation Mechanism: Criegee Intermediate Vinyl hydroperoxide Is there a saddle point in the dissociation of vinyl hydroperoxide (VHP)?

4 There is a Saddle Point! Decomposition of VHP: Found by Kurten and Donahue using very high level computational study MRCISD(4,4)+Q/cc pvtz Kurten, T.; Donahue, N. M. MRCISD Studies of Dissociation of Vinylhydroperoxide, CH2CHOOH: There Is a Saddle Point. J. Phys. Chem. A 2014, 116, VHP goes through transition structure (IV) 2. O O homolysis forms two moieties, held by hydrogen bond (V) 3. Two moieties separate (VI + VII)

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6 Research Overview I. Find a smaller yet accurate level of theory and basis set I. Adding R groups to VHP and exploration of new VHP pathways I. Exploration of other possible reactions of the VHP formed in Isoprene Ozonolysis

7 Finding an Accurate, Smaller Level of Theory and Basis Set Combination Level of theories: B3LYP, BP86, M06L, and M062X Basis Sets: 6 31+G(d,p) and aug cc pvtz

8 Isolation of structure III Procedure Subsequent coordinate scans by increasing O O bond lengths to find max energy TS IV Additional lengthening coordinate scans to find min. energy V Finding energy for VI + VII Important keywords for diradical character U before theory name guess=mix and scf=xqc in the input file opt(addredun) for all coordinate scans

9 Results and. Failure!

10 Not so Rad NOT TS IV TS IV We had been using the wrong structure for TS IV in our theory/basis set analysis, putting us back at square 1!

11 BP86/6 31+G(d,p) Justification Our BP86/6 31+G(d,p) combination gives close results to literature values reported by Kurten and Donahue, so we decided to stay the course and use this level of theory and basis set.

12 Scheme C: Formation of and Competing Pathways for VHPs Two possible reaction pathways, with resulting structures IX, or VI and VII

13 1,4 Hydrogen Shift of Criegee Intermediate to Form Vinyl Hydroperoxide

14 Adding R Groups to VHP BP G(d,p) R 1, R 2, and R 3 are either H or CH 3 8 possible combinations Calculating zero point corrected relative energies with proper scaling factor of *Proper scaling factor taken from Computational Chemistry Department at the University of Minnesota, using BP G(d)

15 1,3 Hydroxyl Shift (Non. OH formation pathway)

16 Scheme C Energies with all Possible R Combinations Adding more methyl groups, TS more stabilized electron density (few deviations) R 1 CH3, difficult to find possible hydrogen interaction and steric effects

17 III TS IV V VII + VII TS II TS VIII TS IV VI + VII I V III IX

18 Ozonolysis of Isoprene

19 Ozonolysis of Isoprene

20 TS II VI + VII TSIV V III

21 Ozonolysis of Isoprene

22 TS II TS VIII I III IX

23 Ozonolysis of Isoprene NOT ISOLATED

24 I TS II TS IV V TS X TS XI III TS XIII XII XIV

25 Relative Energy Summary

26 TS XI Acquired this structure while trying to scan from V to XII Appears that an H 2 O molecule is leaving (Bond angle 109 ) Future research to look into whether or not this is actually viable (seems unlikely) More likely a result of scanning bond distances unrealistically

27 Summary The BP86/6 31+G(d,p) theory/basis set combination gives relatively accurate results in a much faster and less demanding manner than the high level computation applied by Kurten and Donahue Increasing methyl groups increases stability of molecules (lowers energy), particularly in radical and diradical species Electron donating groups stabilize radicals In isoprene ozonolysis, there is indeed a pathway straight from III to XIV via TS X (previously unconfirmed)

28 Future Work Check to see if there is a better level of theory/basis set combination that we can use to analyze these reaction pathways It should not be too hard to use our existing geometries to then isolate structures using a different combination Find transition states we were unable to find (may need larger theory/basis set combination)

29 Acknowledgements Professor Keith T. Kuwata Professor Rebecca C. Hoye Dan Yonker (Hope College)

30 References Kurten, T.; Donahue, N. M. "MRCISD Studies of the Dissociation of Vinylhydroperoxide, CH2CHOOH: There Is a Saddle Point." J. Phys. Chem. A 2012, 116, Kuwata, K. T.; Hermes, M. R.; Carlson, M. J.; Zogg, C. K. "Computational Studies of the Isomerization and Hydration Reactions of Acetaldehyde Oxide and Methyl Vinyl Carbonyl Oxide." J. Phys. Chem. A 2010, 114, Kuwata, K. T.; Templeton, K. L.; Hasson, A. S. "Computational Studies of the Chemistry of Syn Acetaldehyde Oxide." J. Phys. Chem. A 2003, 107,