DFT Study of Intermolecular [4 + 2] versus [3 + 2] Cycloadditions in the Dimerization of 2,4,6-Trinitrotoluene (TNT): Regioselectivity and Stereoselectivity
journal contributionposted on 21.01.2010 by Xiao-Fang Chen, Chun-Yuan Hou, Ke-Li Han
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Two novel types of intermolecular hetero cycloadditions in the participation of the nitro group are put forward in the dimerization of TNT, in comparison with Diels−Alder cross-linking of benzene ring skeletons. Possible transition states and products; for example, their geometrical details, vibrational frequencies, and energies are verified at the B3LYP/6-31+G(d,p) level. Contrary to the hetero Diels−Alder reaction, the folding of the benzene ring side endo is slightly selective specific in 1,3-dipolar cycloaddition. The substituent pattern on reactivity indicates that the methyl group at the bridged sites significantly retards the reaction. Two new σ bonds are formed kinetically and thermodynamically through the single state; however, the first σ bond is more easily generated by the triplet state. The shock-wave-produced chemically bound dimer of TNT is most likely to be the oxygen−carbon linkage product. The initial chemical events in TNT under high pressure can be extended to interpret the shock insensitivity of other unsaturated nitro-explosives. The calculated results agree well with some experimental observations.