The conical intersections (CIXs) for the cis-trans photoisomerization of simple ethylenoids, such as ethylene, styrene and stilbene, have been calculated by complete active space self-consistent-field method. This is because we check if a simple relationship which is found in the case of fluorene-based ethylenoids is also true for simple ethylenoids. Thereby, the four CIXs, which are distinguished by the directions of wagging and rocking motions of the anionic part against the ethylenic bond, are found to be related with the torsional direction of the ethylenic bond after electronic relaxation at each CIX. (C) 2015 Elsevier B.V. All rights reserved.