The influence of substituents on the equilibrium bisnorcaradiene–[10]annulene. The crystal and molecular structure of 11,11‐dimethyltricyclo[4,4,1,01,6]undeca‐2,4,7,9‐tetraene

and oxazine rings, though this conformation along C(4)-C(21) should be sterically unfavourable. In fact, the oxygen atom is at a minimum possible distances from C(22) (2.704 A) and t-I(22) (2.30 ~). These values are a little smaller than the normal intramolecular distances listed by Haschemeyer & Rich (1967). Other short intramolecular distances are N-H(62) (2.30 .~) and O-H(6C) (2.36 ~). The oxazine molecules are packed three-dimensionally with van der Waals contacts, the shortest intramolecular distances being 3.66 ./~ between Br and C(22) and between N and C(62) of two neighbour molecules. Intermolecular distances less than 4.00 A are showed in Fig. 3.