Structure, topological electron density analysis and aromaticity of 4‐heterosubstituted methylenecyclopropenes: X XCH2, NH, O, SiH2, PH and S

Abstract The structures of a series of heterosubstituted methylenecyclopropenes and methylenecyclopropanes were optimized at the HF/6–31G* level. All methylenecyclopropenes are planar except for the silicon analogue, which is bent at both C‐3 and Si. The planar silicon structure is a transition state. The relative aromaticity of these compounds were evaluated using the C‐1C‐3 bond length, the integrated charge on C‐3 and the heteroatom, and delocalization energy. Second‐row systems have slightly larger delocalization energies than their first‐row counterparts, owing to their larger polarizability. Using these criteria, methylenecyclopropene and the silicon analogue are not aromatic and the N, O, P and S analogues are moderately aromatic. The planar silicon analogue is antiaromatic and bends from planarity to reduce this antiaromaticity.