Molecular structure of 10-bromo-9-triptycyl iodoformate: a molecule with a unique functional group

Abstract

9-Triptycyl iodoformate (Ia), unique in containing a stable iodoformyl substituent, was subjected to X-ray crystallographic study to determine whether the conformation throws light on its unexpected stability. Although attempts to solve the structure were unsuccessful, that of the 10-bromo-derivative (Ib) was determined. Crystals are orthorhombic, a= 30.550(5), b= 8.255(5), c= 14.040(5), space group Pbca, Z= 8. This structure was solved by Patterson and difference-Fourier methods, and refined by the method of least squares to R 0.105 for 941 reflections. The molecule is characterised by an unusually short C–1 bond length of 1.98(3)Å and a large number of crowded intramolecular contacts, particularly between the carbonyl oxygen and neighbouring aromatic carbon and hydrogen atoms. These features are discussed in relation to the stability of the iodoformyl group.