Theoretical study of the gas-phase acidity and aromaticity of a novel derivative of nitrogen squaric acid

Molecular geometries of nitrogen squaric acid and its dimeric derivative were optimized at RHF/6-311+G** and RB3LYP/6-311+G** levels of theory. The gas-phase acidity and aromaticity of them were estimated by use of free energy of deprotonation, aromatic stabilization energies (ASE)-based on different homodesmotic reaction schemes, geometry, magnetism-based NICS, NICS(1), and Λ. The calculated ΔG1(298K)0 and ΔG2(298k)0 suggests that the two molecules are all organic acid, and dimeric derivative is a stronger organic acid. The geometric, energetic, and magnetic criteria indicate nitrogen squaric acid is aromatic, and the dimer should only be considered as partly aromatic.