Experimental investigation of the bonding characteristics and charge distribution of a nitrogen ylide by high resolution X-ray diffraction

Abstract

The experimental charge density of trimethylammonionitramidate, (CH₃)₃N⁺–N^- –NO₂, has been determined by high resolution X-ray diffraction. We find the distribution of charge to be more complex than the Lewis formula suggests. Despite the fact that the trimethylammonium fragment bears a full positive charge, the ’onium nitrogen is determined to have a substantial negative charge due to electron donation from the methyl groups by the alkyl inductive effect. The formally negative nitrogen atom of the N⁺–N^- bond has its charge substantially reduced by the electron-withdrawing nitro group considerably stabilising the molecule. The topological properties of the -∇²ρ(r) distribution for this nitrogen atom suggest it to be sp² hybridised.