A series of a-monosubstituted cyclododecan-1,2-dione monooxime were prepared by the reaction of a-monosubstituted cyclododecanone and nitrosyl chloride, and their structures were confirmed by the ¹H NMR, ¹³C NMR, ESI-MS and elemental analysis data. X-ray diffraction and quantum mechanics calculation results showed that the products take two different [4233]-3-one and [3333]-2-one conformation, a-substituted groups present at a-side-exo or a-corner-anti position, the C＝N and C＝O double bonds present at side chain with the torsion angles in the range of 162°～174°, and the C＝N double bond of oximes have E-configuration when they are synthesized with the reaction of a-monosubstituted cyclododecanone and nitrosyl chloride. These two different conformations exist in a dynamic equilibrium with the C₂-pseudorotation transferring pathway in the solution, and the preferred conformation was taken when it crystallized from the solution. The analysis of structure characteristics indicated that p-p and p-p interaction may be the main factor which makes the skeleton conformation change of the twelve-membered ring of a-monosubstituted cyclododecan-1,2-dione monooxime.

Key words: a-monosubstituted cyclododecan-1,2-dione monooxime, X-ray diffraction, quantum mechanics calculation, conformation analysis