The Crystal and Molecular Structure of 2-Bromomethyl-2,3-dihydrofuro[2,3-b]tropone

Abstract

Abstract Crystals of 2-bromomethyl-2,3-dihydrofuro[2, 3-b]tropone, C10H9O2Br, are monoclinic, with four molecules in a unit cell of the dimensions: a=8.34, b=10.23, c=11.26 Å, and β=96.9°, and with the space group of P21⁄c. The intensities were recorded on multiple-film equi-inclination Weissenberg photographs and measured visually against a standard scale. The structure was solved by the heavy atom method. The positional and thermal parameters were refined by the least-squares method. The final R factor for (hkl) reflections is 0.095. An apparent bond alternation in the conjugated seven-membered ring is observed. The longest and the shortest bond lengths in the ring are 1.48 and 1.36 Å respectively. The C–O bond length in the carbonyl group is 1.23 Å, suggesting a considerable contribution of ionic resonance forms. The IR absorption band at 1612 cm−1 could be assigned to the stretching frequency of the carbonyl group. The seven carbon atoms in the tropone ring are coplanar, but the oxygen atom in the carbonyl group lies significantly out of the seven-membered ring plane. This may be interpreted as a result of short intermolecular contact. The other intermolecular distances are equal to or larger than the sum of the van der Waals radii.