The confonnation of α，α'-cis-bissubstituted Cyclododecanones has been studied by means of molecular dynamics computations, 'H NMR, 13C NMR and X-ray diffraction analysis. The results indicate that the ring skeleton of their preferred confonnation is still [3333]-2-one confonnation. Both in crystal and solution, the preferred confonnation of α，α'-cis-bissubstituted Cyclododecanones is α-corner-syn-,α'- side-eso-bissubstituted [3333]-2-one conformation. In solution, the α， α'-cis-bissubstituted Cyclododecanones with the same substituted groups may adopt two conformations, which are mirror image to each other and exist in a dynamic equilibrium, while the α，α'-cis- bissubstituted Cyclododecanones with the different substituted groups may adopt two different [ 3333 ]-2-one conformations: one with the bigger group present in the a-side-exo position, and the other with the bigger group present in the a -corner- syn position, which also exist in a dynamic equilibrium and the former is much more preferred.

Key words: cyclododecanone, CONFORMATION, MOLECULAR MECHANICS, XRD, 1HNMR, C13NMR