Substituent effect on molecular geometry and aromaticity of symmetric B-trisubstituted borazine

Theoretical calculations have been performed to investigate the substituent effect on molecular geometry and aromaticity of the symmetric B-trisubstituted borazine. Deactivating (electron-withdrawing) substituents tend to shorten the B-N bond, decrease the ∠B-N-B angle and increase the ∠N-B-N angle; while activating (electron-donating) substituents induce the contrary geometric variations. Energetic and magnetic criteria have been used to investigate the molecular aromaticity of the symmetric B-trisubstituted derivatives of borazine. NICSzz(2) is found to be a reliable measure of the aromaticity for derivatives of borazine and taken as the major criterion in the present study. Meta directing and deactivating substituents tend to enhance the molecular aromaticity; while ortho-para directing and deactivating substituents as well as ortho-para directing and activating substituents tend to decrease it.