Synthesis and spectroscopy of nitroaceanthrylenes and nitroaceanthrenes

Abstract

AbstractThe syntheses of nine mononitro derivatives of aceanthrylene (1) and nine mononitro derivatives of aceanthrene (2) are described. In addition to 1 and 2, 1,2,6,10b‐tetrahydroaceanthrylene (3), 6,10b‐dihydro‐2(1H)‐aceanthrylenone (5), 1(2H)‐aceanthrylenone (4) and 2(1H)‐aceanthrylenone (8) were also used as starting materials. The resulting nitroaceanthrylenes and nitroaceanthrenes were characterized by their 1H‐NMR, 13C‐NMR, UV‐VIS, IR and mass spectra. The conformation of the nitro group and the interaction between the nitro group and the aromatic system are discussed. In 2‐nitroaceanthrylene (1b), the nitro group interacts exceptionally well with the aromatic nucleus. The 3‐, 4‐, 8‐ and 9‐nitro derivatives of 1 and 2 display all the characteristics of normally conjugated planar nitroaromatic compounds. In the remaining nitro derivatives of 1 and 2, conjugation is diminished owing to steric interactions with nearby protons. The order of decreasing conjugation and increasing twist angle is 5‐nitro > 7‐nitro > 6‐nitro > 10‐nitro. The twist angle of the nitro group was calculated using semi‐empirical SCF methods PM3 and AM1. Although the values obtained by these methods deviate substantially, they both give the same order of increasing twist angles as the spectroscopically derived order.