THE CONFORMATIONAL EFFECT OF 6-MONO-SUBSTITUTED AND 6, 7-DI-SUBSTITUTED DERIVATIVES OF 5, 6, 7, 8-TETRAHYDRODIBENZO [A, C] CYCLO-OCTENE ON 13C CHEMICAL SHIFT

Abstract

Hartree-Fock (HF) and Density Functional Theory (DFT) methods employed to study the effect of conformational change on the 13 C chemical shifts of 6-mono axial and equatorial substituted and 6,7-di axial-axial, equatorial-equatorial and axial-equatorial substituted derivatives of 5,6,7,8-tetrahydrodibenzo(a,c)cyclo-octene. The geometry of the conformers have been optimized in the gas phase employing the 6-311G(d,p) basis set. The 13 C chemical shifts were calculated by Gauge Including Atomic Orbitals (GIAO) method. The correlation between calculated 13 C chemical shifts in the gas phase and experimental ones in CDCl3 solvent is linear with squared regression coefficient of 0.96. Also the calculated 13 C 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 13 C chemical shifts of the axial and equatorial substituted carbon atoms are more due to the paramagnetic than the diamagnetic shielding.