Aromatic Character Studies on Calicene and Its Derivatives Containing Heavier Atoms via Nuclear Independent Chemical Shifts (NICS)

Abstract

DFT calculations were carried out on the molecular structure of calicene and its derivatives containing heavy atoms, 1_X and 2_X (X˭C, Si, Ge and Sn), using 6-311+G** basis set in the GAUSSIAN 98 program. The aromatic character of 1_X and 2_X was investigated through the magnetic and the geometric criteria. From a geometric view, the molecules, 1_C , 1_Si , 1_Ge , 1_Sn and 2_Si have completed electron current in the three-member ring, while the molecules 2_Ge and 2_Sn have completed electron current in the five-member ring. Nuclear independent chemical shifts NICS (0.5) calculations indicated an aromatic character in both three and five rings of 1_X and 2_X , which was decreased from X˭C to X˭Sn (except for 1_Sn ). However, a non-aromatic and an aromatic character at three- and five-membered ring were observed for 2_Sn , respectively.

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Keywords:

• Aromatic character
• calicene
• cyclopropenylidenecyclopentadiene
• heavy atoms
• molecular structure
• NICS

Acknowledgments

Payame Noor University (PNU) is gratefully acknowledged due to their financial support of this research.