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

The experimental charge density of trimethylammonionitramidate, (CH3)(3)N+-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 - del(2) rho(r) distribution for this nitrogen atom suggest it to be sp(2) hybridised.