Summary. The structures and relative energies of fundamental conformations of cyclopenta-1,2,3-triene, cyclohexa-1,2,3-triene, cylohepta-1,2,3-triene,
cycloocta-1,2,3-triene, and cyclonona-1,2,3-triene were calculated by the HF/6-31G
* and MP2/6-31G
*//HF/6-31G
* methods. Only a
C
2v symmetric planar conformation is available to cyclopenta-1,2,3-triene and cyclohexa-1,2,3-triene. The calculated energy barrier
for ring inversion of the
C
S symmetric puckerd conformation of cyclohepta-1,2,3-triene
via the planar geometry is 62.2 kJ·mol
−1. The
C
2 symmetric twist conformation of cycloocta-1,2,3-triene was calculated to be the most stable one. Conformational racemization
of the twist form takes place
via the
C
S symmetric half-chair geometry, which is by 60.8 kJ·mol
−1 less stable than the twist conformer. The
C
S symmetric chair and unsymmetrical twist-boat conformations of cyclonona-1,2,3-triene were calculated to have similar energies;
their interconversion takes place
via an unsymmetrical low-energy (18.4 kJ·mol
−1) transition state. The twist (
C
2) and boat (
C
S) geometries of cyclonona-1,2,3-triene are higher in energy by 13.2 and 33.9 kJ·mol
−1, respectively. Ring inversion in chair and twist-boat conformations takes place
via a twist form as intermediate and requires 33.6 kJ·mol
−1.
Corresponding author. E-mail: isayavar@yahoo.com
Received March 25, 2002; accepted April 4, 2002
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