Abstract
Crystallographic investigations have been carried out on 11H-benzo[b]indeno[3,2-e] pyran and its 2-bromo-substituted derivative, and the crystal structure of both compounds has been determined. The intensity data for both compounds was collected on a 4-circle single-crystal diffractometer. A small section of this work has been devoted to the practical details relating to the mode of operation of this instrument. 2-bromo-11H-benzo[b]indeno[3,2-e] pyran crystallises in the monoclinic system: a = 7.508, b = 5.959, c = 26.172 A, mu = 92.55°, ? = 4, space group P21/c. The structure was solved by Fourier methods and refined by full-matrix least squares to R = 0.072. 11H-benzo[b]indeno[3,2-e] pyran crystallises in the orthorhombic system; a = 22.425, b = 5.816, c = 16.398 A, ? = 8, space group Pca21. This structure, solved by direct methods and refined by full-matrix least squares to R = 0.122, is characterised by having two molecules per asymmetric unit related by a pseudo-centre of symmetry. Both molecules show a non-planar configuration and lack of aromatic character within their central regions. Molecular orbital calculations by Huckel and CNDO methods have been carried out on both molecules and a comparison of the calculated and experimental bond lengths has been made. The results of these calculations have also been used in an attempt to explain the characteristic mode of packing of the two molecules.