The Conformational Effect of ۶-Mono-Substituted and ۶,۷-Di-Substituted Derivatives of ۵,۶,۷,۸-Tetrahydrodibenzo[a,c]cyclo-octene on ۱۳C Chemical Shift

Hartree-Fock (HF) and Density Functional Theory (DFT) methods employed to study the effect of conformational change on the ۱۳C chemical shifts of ۶-mono axial and equatorial substituted and ۶,۷-di axial-axial, equatorial-equatorial and axial-equatorial substitutedderivatives of ۵,۶,۷,۸-tetrahydrodibenzo[a,c]cyclo-octene. The geometry of the conformers have been optimized in the gas phase employing the ۶-۳۱۱G(d,p) basis set. The ۱۳C chemical shifts were calculated by Gauge Including Atomic Orbitals (GIAO) method. The correlation between calculated ۱۳C chemical shifts in the gas phase and experimental ones in CDCl۳ solvent is linear with squared regression coefficient of ۰.۹۶. Also the calculated ۱۳C chemical shift in the gas phase by the HF method shows better correlation with experimental ones compared with DFT method. Calculations of both the paramagnetic and diamagnetic shielding of carbon atoms demonstrate that the difference between experimental ۱۳C chemical shifts of the axial and equatorial substituted carbon atoms are more due to the paramagnetic than the diamagnetic shielding.

کلیدواژه ها:

۱۳C chemical shift ، Diamagnetic shielding ، Paramagnetic shielding ، NMR ، GIAO method ، Conformation ، Eight membered rings