Crystal and molecular structure of 4,10-dibromo-1,7-methano[12]annulene

Abstract

An X-ray crystal structure determination of the title compound (I)(monoclinic, space group C2/c, a= 14.929(2), b= 4.281 (1), c= 18.630(2)Å, β= 100.60(1)°, Z= 4) shows systematic alternation of long and short bond distances (means 1.46 and 1.34 Å) in the perimeter ring. The configuration of the double bonds follows the order trans, cis, cis. The molecule has a twisted conformation and crystallographic symmetry 2 (C₂), with the two-fold axis running through the carbon atom of the methano-bridge. Simple HMO calculations for the present compound and other [4n]annulenes are in quite good agreement with experimental results. The structure was determined by the heavy-atom method and refined by least-squares techniques to R 0.037 for 1 249 observed reflections measured by diffractometer.