Theoretical study on the small carbon nano-ladders

Abstract

1,3-Butadiyne, 1,3,5-hexatriyne, 1,3,5,7-octatetrayne, and 1,3,5,7,9-decapentayne are small oligomeric forms of acetylene. These oligomers participate in cyclization reactions to form ladder-like structures. Enthalpies, ∆H, and Gibbs free energies, ∆G, of the cyclization reactions were calculated employing MP2 and B3LYP methods. The calculated ∆H and ∆G were positive, and their variation versus carbon atoms number, n, was fitted in linear functions as ∆H(n) = a+bn. The calculations were performed on the structures with carbon numbers up to 20. Also, consecutive cyclization reactions between acetylene molecules were studied. During these consecutive reactions, two different structures, zigzag-ladder-like and cyclic molecules with tetragonal rings, were produced. Among the cyclic structures, the hexagonal form was the most stable structure. The calculated ∆H and ∆G of formation of zigzag-ladder-like molecules were excellently fitted in linear functions. The obtained functions for ∆H and ∆G calculated by MP2 method are ∆H(n) = 139.67−126.44n and ∆G(n) = 80.987−75.684n, respectively.