• Xiaojun Tan

      Articles written in Journal of Chemical Sciences

    • Theoretical insights into the cycloaddition reaction mechanism between ketenimine and methyleneimine: An alternative approach to the formation of pyrazole and imidazole

      Nana Wang Xiaojun Tan Weihua Wang Fangfang Wang Ping Li

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      The cycloaddition reaction mechanism between interstellar molecules, ketenimine and methyleneimine, has been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method in order to better understand the reactivity of nitrogenous cumulene ketenimine with the C=N double bond compound methyleneimine. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. Calculations show that five-membered cyclic carbene intermediates could be produced through pericyclic reaction processes between ketenimine and methyleneimine. Through the subsequent hydrogen transfer processes, carbene intermediates can be isomerized to the pyrazole and imidazole compounds, respectively. The present study is helpful to understand the formation of prebiotic species in interstellar space.

    • Insights into the insertion reaction mechanism of phosphenium cation and oxirane: a theoretical study

      Xiaojun Tan Yingxin Mao Guizhi Shi Huilian Xu Yan He Jinsong Gu

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      The mechanism of insertion reaction between phosphenium cation and phosphindene with oxirane has been investigated theoretically to better understand the reactivity for the valence isoelectronic of carbene. Phosphenium cation acts as an electrophilic reagent and accepts σ electrons of oxirane to form a complex in the first combination step. The greater the positive charge on phosphorus in phosphenium cation, the more stable the formed complex is. The introduction of substituents will decrease the positive charge on phosphorus in phosphenium cation. The order of positive charge on phosphorus is HP+-F > HP+-OH > HP+-NH2, which is consistent with their Lewis acidities. The complex transforms to a four-membered ring product via a transition state in the second insertion step. The product is more stable than the complex due to the decrease of ring extension.

      Phosphenium cation acts as an electrophilic reagent and accepts σ electrons of oxygen in oxirane to form a four-membered ring product. The introduction of substituents will decrease the positive charge on phosphorus in phosphenium cation, which reduced the stability of the products.

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