The conformation of the bicyclo(3,3,1)nonane system from x-ray studies

X-ray data of eleven compounds containing the bicyclo(3,3,1)nonane system were analysed in order to study its conformation. From the available data, the structures have been subdivided into four major groups depending upon the conformation taken up in the crystal structure and also based on chemical classification of the bicyclo(3,3,l)nonane system. It was found that in the majority of the cases reported, the system exists in the 'chair-chair' form. However, in certain cases, especially when there are bulky substituents at positions 3 or 7, the system adopts the 'chair-boat' conformation. The interesting conformational features of the four major groups are discussed in terms of their bond lengths, bond angles and torsion angles.