Ab initio study of bridged biphenylene systems containing a nine-membered ring

Abstract

The conformational properties of bridged biphenylenes in which the C-1 and C-8 atoms of the biphenylene ring are bonded by five atoms in a bridging chain Z (Z(CH 2) 5, 1; (CH 2) 2O(CH 2) 2, 2; (CH 2) 2S(CH 2) 2, 3) were studied using ab initio molecular orbital and density functional theory methods. Studies on the HF/631G* level of theory revealed that for compounds 1 and 3, plane symmetrical boat conformation was found to be the lowest energy. For compound 1, the twist, twist-boat and chair conformations are less stable by 0.76, 1.85 and 4.28 kcal mol −1, respectively, as calculated by HF/6-31G* method. Also, HF/6-31G* results for compound 3, show that the twist, twist-boat and chair conformations are less stable by 2.41, 5.02 and 2.62 kcal mol −1, respectively. However, contrary to compounds 1 and 3, twist conformation ( C 1 symmetry) was found the most stable form for compound 2. For compounds 1– 3, there is a good agreement between HF/6-31G*//HF/6-31G*, MP2/631G*//HF/6-31G* and B3LYP/6-31G*//HF/6-31G* obtained results.