Structure-Reactivity Studies by NMR Spectroscopy and Molecular Orbital Calculation: Nitration of Polycyclic Aromatic Ketones

Abstract

Complete assignments of NMR spectra were made for benzanthrones, using 2D correlation spectroscopic techniques of homonuclear H-H COSY and NOESY and heteronuclear CH-COSY and COLOC methods. The nitration positions for 6H-benzo[cd] pyren-6-one (1), 13H-dibenzo[a, de]anthracen-13-one (2), 7H-benzo-[hi]chrysen-7-one (3), 7H-dibenzo[a, kl]anthracen-7-one (4), 5H-benzo[fg]naphthacen-5-one (5) and 7H-benzo[de]anthracen-7-one (6) were determined on the basis of the weak or negative NOE cross peaks, which agreed with the results of the absolute values and phase sensitive 2D NOESY experiment. The nitration positions for the benzanthrones were explained by the appearance of negative or weak NOE cross peaks in the 2D NOESY spectra. Molecular orbital calculations also showed that (1), (2), (4) and (6) have the largest electron densities of the highest occupied molecular orbitals at the carbon atoms where nitration takes place. A correlation can be seen between the 2D NOESY spectra and molecular orbital calculations with respect to the position of nitration.

Key Words:

• benzanthrones
• NMR
• weak NOE cross peak
• negative NOE cross peak
• molecular orbital calculation
• nitration