Ab initio study of conformational properties of cycloocta-1,5-diyne, cyclonona-1,5-diyne and cyclodeca-1,6-diyne

The structure and relative energies for the basic conformations of cyclooct a-1,5-diyne (1), cyclonona-1,5-diyne (2), and cyclodeca-1,6-diyne (3) have been calculated by the split-valence 6-31G* basis set. The chiral puckered conformer of 1, with a "non-intersecting" twofold axis of symmetry, is calc ulated to be more stable than the planar, D-2h, geometry. The plane-symmetr ical envelope geometry of 2 is calculated to be a transition-state, separat ing the unsymmetrical envelope conformers. Ring inversion of the envelope c onformation takes place via twist, C-2, transition-state. The chair and boa t conformers of 3 have virtually the same energies, and their interconversi on take place via the half-chair transition-state. (C) 2001 Elsevier Scienc e B.V. All rights reserved.