Polyyne oligomers (H2CnH2), with CH2 group at each end of the oligomer, have been found to give helical molecular orbitals for the HOMO and LUMO and other molecular orbitals around the HOMO and LUMO when the two CH2 groups are tilted from their equilibrium positions. This can be explained by the changes in the symmetry of H2C2m+1H2 from D-2d to D-2, the former having degenerate molecular orbitals but the latter having non-degenerate orbitals. These helical molecular orbitals have been pointed out as being a kind of molecular device through which electrons pass. (C) 2013 Elsevier B. V. All rights reserved.