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Download fileSoot Platelets and PAHs with an Odd Number of Unsaturated Carbon Atoms and π Electrons: Theoretical Study of Their Spin Properties and Interaction with Ozone
journal contribution
posted on 2008-02-07, 00:00 authored by Anna Giordana, Andrea Maranzana, Giovanni Ghigo, Mauro Causà, Glauco TonachiniPAHs made from an odd number of unsaturated carbon atoms and π electrons (odd PAHs) have been detected
in flames and flank the more familiar even PAHs, having approximately the same quantitative importance,
particularly for PAHs containing more than 25 carbon atoms. Similarly, soot platelets containing an odd
number of carbon atoms can be reasonably assumed to form during combustion. PAHs are intended here as
small models for the investigation of some of their local features. To this end, quantum mechanical calculations
were also carried out on periodic models. The spin density patterns were found to be highly dependent on the
PAH size and shape. PAHs and soot, once released in the environment, can undergo several oxidation processes.
Ozone is then taken as a probe of the reactivity properties of some internal exposed portions of a platelet. A
primary ozonide (PO) corresponds to an energy minimum, but the relevant concerted addition pathway does
not exist, because a PO-like saddle point is second-order. The reaction begins with a nonconcerted attack that
produces a trioxyl radical (TR). Subsequent O2 loss from the TR leaves either an epoxide with a π-delocalized
electron or a π-delocalized oxepine, by cleavage of the ring carbon−carbon bond. The initial doublet spin
multiplicity thus provides a description of the reaction surface unlike that for the internal reactivity of the
closed-shell even systems investigated in a previous work, even though the final functionalization is the
same.