A proton and carbon NMR spectroscopic study of 5‐substituted acenaphthenes

Abstract

The proton and carbon NMR spectra of eight 5-substituted acenaphthenes were obtained. The 13C chemical shifts of C-6 and C-2a of these compounds were compared with those of carbons located at structurally similar positions in 1-substituted naphthalenes (viz. C-8 and C-4). The 13C chemical shifts of C-2a were also analysed using the dual substituent parameter (DSP) equation. The results revealed (i) diminished steric interactions between the 5-substituent and the adjacent peri-carbon (C-6) and (ii) an enhanced transmission of both polar and resonance effects to the carbon para (C-2a) to the variable substituent, X, in acenaphthenes relative to the corresponding carbons (C-4) in 1-substituted naphthalenes. The higher ρI and ρR values observed for C-2a of acenaphthenes suggest higher polarizability in this system than in naphthalenes. AM1 calculations of charge also showed enhanced substituent effects in the case of most of the substituents in the acenaphthene system. © 1998 John Wiley & Sons, Ltd.