Halogen effect on structure and ¹³C NMR chemical shift of 3,6‐disubstituted‐N‐alkyl carbazoles

Abstract

Structures of selected 3,6-dihalogeno-N-alkyl carbazole derivatives were calculated at the B3LYP/6-311++G(3df,2pd) level of theory, and their (13) C nuclear magnetic resonance (NMR) isotropic shieldings were predicted using density functional theory (DFT). The model compounds contained 9H, N-methyl and N-ethyl derivatives. The relativistic effect of Br and I atoms on nuclear shieldings was modeled using the spin-orbit zeroth-order regular approximation (ZORA) method. Significant heavy atom shielding effects for the carbon atom directly bonded with Br and I were observed (~-10 and ~-30 ppm while the other carbon shifts were practically unaffected). The decreasing electronegativity of the halogen substituent (F, Cl, Br, and I) was reflected in both nonrelativistic and relativistic NMR results as decreased values of chemical shifts of carbon atoms attached to halogen (C3 and C6) leading to a strong sensitivity to halogen atom type at 3 and 6 positions of the carbazole ring. The predicted NMR data correctly reproduce the available experimental data for unsubstituted N-alkylcarbazoles.

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

“…4 that the spin-orbit effects played a major role in the calculations of chemical shifts of carbon atoms directly attached to the halogen atom (here iodine). The observed HALA effects are very close to earlier results for halogen-substituted carbon atoms [15,35,42]. The other carbons, however, do practically not feel the presence of the heavy halogen atoms.…”

“…One of the most common carbazole derivatives applied in electrophotographic [8] is poly (N-vinylcarbazole). The 3,6-and 2,7-substituted carbazole derivatives are currently among the most widely studied materials [11][12][13][14][15]. It is known that the presence of heavy atoms (Cl and Br) decreases the relative quantum yield of fluorescence and increases phosphorescence in the carbazole derivatives [16].…”

“…Nowadays, the assignment of experimental spectra is often supported by molecular modeling of the relevant NMR parameters [19][20][21], as it is possible to predict satisfactory chemical shifts for several different nuclei including 13 C, 17 O, 15 N, and 19 F [19,[22][23][24][25] using density functional theory (DFT) calculations in combination with gauge including atomic orbitals (GIAOs [26,27]) and employing the Becke three-parameter, Lee-Yang-Parr (B3LYP [27,28]) or the hybrid half-and-half (BHandHLYP) exchange correlation functionals [29]. Several NMR reports on the simplest carbazoles are available [30][31][32][33].…”

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

“…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…”

DFT studies on armchair (5, 5) SWCNT functionalization. Modification of selected structural and spectroscopic parameters upon two-atom molecule attachment

“…Its excellent performance was recently confirmed. [47][48][49] The nuclear magnetic shielding tensor ij  (in ppm) of i-th nucleus [29,50,51] was calculated as a second derivative of the total energy (E) with respect to nuclear moment ( i  ) and magnetic field (B j ):…”