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Determination of geometric parameters of the terpenoid 18á-oleanane by quantum chemistry methods

Djeradi Houria, Rahmouni Ali, Cheriti Abelkrim*

A comparative study using ab initio calculation (HF/6-31G), semi empirical (PM3) and DFT (B3LYP/6-31G) shows a high correlation with the geometric data of x-ray diffraction of the terpenoid 18á-oleanane (C32H52O3), crystallizes in space group C2 with a = 13.3520 (2), b = 6.54000 (10), c = 32.4439(5) Å, V = 2798.13(7) Å3 and Z = 4. The theoretical results were compared to experimental data generated by x-ray diffraction, the difference between the calculated and experimental values is very insignificant. The structure was refined to a final R = 0.027 for the structure factors observed with I  3ó(I).