Ab initio study of the conformational properties of (Z,Z)-cyclodeca-1,6-diene and its heterocyclic analogue containing oxygen

Ab initio molecular orbital and density functional theory methods were used to investigate the structure and conformational interconversion of (Z,Z)-cyclodeca-1,6-diene (1) and (Z,Z)-1,6-dioxa-cyclodeca-3,8-diene (2). Consistent with the previously reported AM1 semi-empirical data, a chair conformation with C2h symmetry is found to be the most stable geometry for compounds 1 and 2. However, further investigations reveal the presence of both two ground states, i.e. 1-Twist-Chair-Boat-Chair (C1 symmetry) and 1-Twist-Boat-Boat-Chair (Ci symmetry) and two transition state structures ([1-Chair→1-Twist-Chair-Boat-Chair]# and [1-Twist-Chair-Boat-Chair→1-Twist-Boat-Boat-Chair]#), which were not previously reported by the AM1 investigation [I. Yavari, M.R. Hosseini-Tabatabaei, D. Nori-Shargh, A. Jabbari, J. Mol. Struct. (Theochem) 574 (2001) 9], and therefore, the correct ring inversion process for compound 1 is now presented. In addition, the conformational properties of heterocyclic analogue of compound 1 (containing oxygen atom), i.e. (Z,Z)-1,6-dioxa-cyclodeca-3,8-diene (2), is also reported in this work.