Molecular modeling and experimental studies on structure and NMR parameters of 9-benzyl-3,6-diiodo-9H-carbazole

A combined experimental and theoretical study has been performed on 9-benzyl-3,6-diiodo-9H-carbazole. Experimental X-ray (100.0 K) and room-temperature C-13 nuclear magnetic resonance (NMR) studies were supported by advanced density functional theory calculations. The non-relativistic structure optimization was performed and the C-13 nuclear magnetic shieldings were predicted at the relativistic level of theory using the zeroth-order regular approximation. The changes in the benzene and pyrrole rings compared to the unsubstituted carbazole or the parent molecules were discussed in terms of aromaticity changes using the harmonic oscillator model of aromaticity and the nucleus independent chemical shift indexes. Theoretical relativistic calculations of chemical shifts of carbons C3 and C6, directly bonded to iodine atoms, produced a reasonable agreement with experiment (initial deviation from experiment of 41.57 dropped to 5.6 ppm). A good linear correlation between experimental and theoretically predicted structural and NMR parameters was observed.