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The Gas-Phase Pyrolysis of Nitrocyclobutanes: a Shock-Tube Investigation Supplemented with DFT Calculations of their Thermochemical and Structural Parameters

Mono- and 1,1-dinitrocyclobutanes (highly diluted in Ar) were pyrolyzed at temperatures 860–1300 K in reflected shocks. Activation energies for their initial fragmentations were derived from measurements of relative rates of species loss, compared to cyclobutyl chloride and isopropyl bromide: kuni(NCB) = 9.66 × 1012 exp (-25264/T), s-1, kuni(DNCB) = 6.26 × 1012 exp (-21087/T), s-1 The production and decay of NO2 was monitored in real time via its absorption at 405 nm. The identity and amounts of the species produced during 1.3 ms residence time were determined by FTIR and GC analysis of samples extracted from the tube terminus, after being quenched by an expansion wave. Plausible mechanisms that account for the observed product distributions are proposed. In a computational Appendix, the results of density functional theory (DFT) calculations are presented for enthalpies and entropies of several mono-substituted cyclobutanes and for 1,1-dinitrocyclobutane, as well as for selected fragmentation products.