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.

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

The (3)He nuclear magnetic shieldings were calculated for free helium atom and He-pyrrole, He-indole, and He-carbazole complexes. Several levels of theory, including Hartree-Fock (HF), Second-order Møller-Plesset Perturbation Theory (MP2), and Density Functional Theory (DFT) (VSXC, M062X, APFD, BHandHLYP, and mPW1PW91), combined with polarization-consistent pcS-2 and aug-pcS-2 basis sets were employed. Gauge-including atomic orbital (GIAO) calculated (3)He nuclear magnetic shieldings reproduced accurately previously reported theoretical values for helium gas. (3)He nuclear magnetic shieldings and energy changes as result of single helium atom approaching to the five-membered ring of pyrrole, indole, and carbazole were tested. It was observed that (3)He NMR parameters of single helium atom, calculated at various levels of theory (HF, MP2, and DFT) are sensitive to the presence of heteroatomic rings. The helium atom was insensitive to the studied molecules at distances above 5 Å. Our results, obtained with BHandHLYP method, predicted fairly accurately the He-pyrrole plane separation of 3.15 Å (close to 3.24 Å, calculated by MP2) and yielded a sizable (3)He NMR chemical shift (about -1.5 ppm). The changes of calculated nucleus-independent chemical shifts (NICS) with the distance above the rings showed a very similar pattern to helium-3 NMR chemical shift. The ring currents above the five-membered rings were seen by helium magnetic probe to about 5 Å above the ring planes verified by the calculated NICS index.

The first report on crystal and molecular structure of 3,6-diiodo-9-ethyl-9H-carbazole is presented. Experimental room-temperature X-ray and 13 C chemical shift studies were supported by advanced theoretical calculations using density functional theory. The 13 C nuclear magnetic shieldings were predicted at the non-relativistic and relativistic level of theory using the zeroth-order regular approximation. 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 44.3 dropped to 4.25 ppm). The changes in ring aromatic character were estimated via a simple harmonic oscillator model of aromaticity and nucleus-independent chemical shift index calculations. A good linear correlation between experimental and theoretically predicted structural and NMR parameters was observed.

Static electric properties, from the dipole moment to the second-hyperpolarizability tensor γ, of the 3membered, isoelectronic ring molecules, fluorene (FL), carbazole (CR), and dibenzofuran (DBF), have been calculated at various levels of approximation. The electron correlation effects have been included at the coupled-cluster (CC) level, using CCSD and CC2 versions of the method. DFT calculations with the CAM-B3LYP functional have also been performed, and the results are compared to the CC values. The electric property-tailored Pol basis set and its more compact Z3Pol version have been employed in all static calculations. Differences between dipole polarizability values computed at the Pol and Z3Pol bases have been found to be almost negligible. Therefore, all components of the frequency-dependent dipole polarizability tensor α(−ω;ω) have been determined at the CAM-B3LYP/Z3Pol level. Divergence occurring at electronic resonances has been eliminated using the complex polarization propagator (CPP) formalism, explicitly introducing an imaginary iΓ parameter to account approximately for the finite lifetime of the excited state. The imaginary part of the dipole polarizability Im α(−ω;ω) has been calculated for a wide range of external radiation energies up to 10 eV, and its maxima have been compared to the calculated vertical electronic excitation energies.

No abstract

No abstract