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Computational Study of the Reaction of 1‑Methyl-4-amino-1,2,4-triazolium Dicyanamide with NO2: From Reaction Dynamics to Potential Surfaces, Kinetics and Spectroscopy

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posted on 21.02.2019, 00:00 by Jianbo Liu, Wenjing Zhou, Steven D. Chambreau, Ghanshyam L. Vaghjiani
Direct dynamics trajectories were calculated at the B3LYP/6-31G­(d) level of theory in an attempt to understand the reaction of 1-methyl-4-amino-1,2,4-triazolium dicyanamide (MAT+DCA) with NO2. The trajectories revealed an extensive intra-ion-pair proton transfer in MAT+DCA. The reaction pathways of the ensuing HDCA (i.e., HNCNCN) and [MAT+ – HC5+] (i.e., deprotonated at C5–H of MAT+) molecules as well as DCA with NO2 were identified. The reaction of NO2 with HDCA and DCA produces HNC­(−ONO)­NCN and NCNC­(−ONO)­N or NCNCN–NO2, respectively, whereas that with [MAT+ – HC5+] results in the formation of 5-O-MAT (i.e., 4-amino-2-methyl-2,4-dihydro-3H-1,2,4-triazo-3-one) + NO and [MAT+ – H2+] + HNO2. Using trajectories for guidance, structures of intermediates, transition states and products, and the corresponding reaction potential surfaces were elucidated at B3LYP/6-311++ G­(d,p). Rice–Ramsperger–Kassel–Marcus (RRKM) theory was utilized to calculate the reaction rates and statistical product branching ratios. A comparison of direct dynamics simulations with RRKM modeling results indicate that the reactions of NO2 with HDCA and DCA are nonstatistical. To validate our computational results, infrared and Raman spectra of MAT+DCA and its reaction products with NO2 were calculated using an ionic liquid solvation model. The calculated spectra reproduced the vibrational frequencies detected in an earlier spectroscopic study of MAT+DCA droplets with NO2 [Brotton, S. J.; J. Phys. Chem. Lett. 2017, 8, 6053].

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