A computational study on the structure of allene polymers by using quantum chemical methods

Abstract

The conformational analysis of 1,3-dicyanodiethynylallene and 1,3- diethynylallene oligomers have been carried out by using quantum mechanical semiempirical AM1 method implemented in G03 and G98.Although chiral 1,3-diethynylallene unit upon forming intramolecular hydrogen bond is expected to form helical oligomers and polymers that have optically active character, our results indicate that the oligomers of this molecule have lack of helicity.Instead, the conformations observed for 1,3-diethynylallene oligomers are all unfolded zig-zag like chains.1,3-dicyanodiethynylallene oligomer, a derivative of 1,3-diethynylallene, is also expected to have a helical conformation. In oligomer structures, the results of optimizations show that 1,3-dicyanodiethynylallene has a well defined three-dimensional helical conformation. This helicity is attributed to electrostatic interactions between cyano carbon which has a high negative charge and oppositely charged allene carbons along the helical axis. We observe P-helix rather than M-helix, no the conformers which may lead to M character is encountered.