Computational study of proton and methyl cation affinities of imidazole-based highly energetic ionic liquids

Abstract

The present study deals with the evaluation of gas phase proton and methyl cation affinities for alkyl- and nitrosubstituted imidazoles using DFT (B3LYP)/6-31 + G(d) and MP2 methods in the Gaussian 03 software package. The extent of charge delocalization of these cations is correlated with proton affinity. The study reveals that weakly electron-donating alkyl groups at position 1 of the imidazole enhance its proton affinity, which also increases with increasing alkyl chain length. This is expected to result in an increased tendency to form salts. In contrast, the presence of strongly electron-withdrawing nitro groups lowers proton affinity, which decreases as the number of nitro groups on the ring increases. The same trend is observed for the methyl cation affinity, but to a lower degree. These trends in the proton and methyl cation affinities were analyzed to study the effects of these substituents on the basicity of the energetic imidazole moieties and their tendency to form salts. This, in turn, should aid searches for better highly energetic ionic liquids. In addition, calculations performed on different isomers of mono and dinitroimidazoles show that 5-nitro-1H-imidazole and 2,4-dinitro-1H-imidazole are more stable than the other isomers. Amongst the many nitro derivatives of imidazoles considered in the present study, cations resulting from these two would be the best choice for creating highly energetic ionic liquids when coupled with appropriate energetic anions.

Complexes of a naphthalimide photoacid with organic bases, and their excited-state dynamics in polar aprotic organic solvents

“…the B3LYP functional because it has been shown to produce reasonable results for 1,8-naphthalimide dyes. 44,45 Secondly, B3LYP has been shown to give reliable values for proton affinities, 46 complexation energies and geometries of bimolecular complexes. 47,48 The conductor-like screening model (COSMO) 49 was used to include solvent effects.…”

Synthesis of New Energetic Materials and Ionic Liquids Derived from Metronidazole

“…Smiglak et al [16] have demonstrated that when the imidazole nucleus is substituted with two or three nitro functional groups the synthesis of the corresponding 1,3dialkylimidazolium or 1-alkyl protonated cations is futile due to their resistance to N-alkylation or protonation, respectively. Such is the case of 1-methyl-2,4-dinitroimidazole and 1-methyl-4,5-dinitroimidazole [16,17]. However, metronidazole has only one nitro functional group within the azole nucleus; thus, it was estimated it would be a suitable candidate for forming various energetic protonated ionic liquids (EPILs).…”