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

Abstract

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 13 C nuclear magnetic resonance (NMR) studies were supported by advanced density functional theory calculations. The non-relativistic structure optimization was performed and the 13 C 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. Graphical AbstractKeywords 9-Benzyl-3,6-diiodo-9H-carbazole Á X-ray structure Á 13 C NMR spectra Á ZORA Á GIAO NMR calculations Á HOMA Á NICS

DFT and experimental studies on structure and spectroscopic parameters of 3,6-diiodo-9-ethyl-9H-carbazole

“…The significant errors with a rootmean-square deviation (RMS) of 6.23 ppm (for SO ZORA calculations RMS = 0.87 ppm) are visible for these two carbon chemical shifts predicted using non-relativistic calculations ( Table 4). The RMS is smaller than for the previously studied 9-benzyl-3,6-diiodo-9H-carbazole [58]. The observed HALA effects are very close to earlier results for halogen-substituted carbon atoms [35,41,66] and for our previous study of benzylcarbazole derivative (there the HALA effect was -42 ppm) [58].…”

“…The RMS is smaller than for the previously studied 9-benzyl-3,6-diiodo-9H-carbazole [58]. The observed HALA effects are very close to earlier results for halogen-substituted carbon atoms [35,41,66] and for our previous study of benzylcarbazole derivative (there the HALA effect was -42 ppm) [58]. The other carbons, especially atoms responsible for the rigidity and planarity Weighting scheme…”

“…These non-relativistic (NR) calculations were carried out using GAUS-SIAN 09 [57]. In our previous work [58], we reported on the structural parameters for 9-benzyl-3,6-diiodo-9H-carbazole obtained at the relativistic (R) SO ZORA (B3LYP/ DZP/TZP) level of theory. These results were of similar accuracy to the results of the non-relativistic calculations.…”

Computational 1H NMR: Part 1. Theoretical background

“…Relativistic effects in NMR chemical shifts and spinspin coupling constants known as "Heavy Atom on Light Atom" (HALA) effects were evaluated in a great number of molecules containing "heavy" elements, see some salient earlier publications [117][118][119][120][121][122][123][124][125][126] together with some more recent and most recent ones [127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][143][144][145] and many other related papers, [146][147][148][149][150][151][152][153][154][155] which are not cited herewith in full in view of their multiplicity.…”

Relativistic heavy atom effect on 13C NMR chemical shifts initiated by adjacent multiple chalcogens

“…The HALA effects induced by neighboring heavy atoms (HAs) on 13 C chemical shifts have been studied for a long time, though, the most part of works deals with the HALA effect induced by the heavy halogens [3,4,[13][14][15][16][17][18][19][20][21][22] or by neighboring heavy transition metals. [6,11,23,24] At the present moment, with the exception for several casual communications, [25][26][27][28] there is no systematic study of the HALA effect on carbon chemical shifts induced by heavy chalcogens.…”