ChemInform Abstract: Structure of 3-Chlorotropolone.

Abstract

C7H5C102, Mr = 156.6, monoclinic, P21/c, a = 8.476 (2), b = 12.241 (2), c = 8.170 (2) A, /3 -- 126.47 °, V= 681.7 A 3, z = 4, Dx = 1.525 g cm -3, A(Cu Ka) = 1.54184 A, /z = 44.63 cm-~, F(000) = 320, T = 293 K, R -- 0.046 for 833 reflections with I > 3tr(I). The hydroxylic proton forms a bifurcated hydrogen bond with carbonyl O atoms, one branch intramolecular and the other intermolecular. The latter intermolecular branches form a hydrogen- bonded dimer, which is roughly planar. Introduction. The structures of tropolone and some tropolone derivatives have been studied. It has been shown that 5,isopropyltropolone (Berg, Karlasson, (P~.tti & Wiehager, 1976) as well as tropolone manouchi & Sasada, 1973) forms a bifurcated hydrogen bond with the carbonyl O atoms, one branch being intramolecular and other intermolecu- lar. On the other hand, 4-isopropyltropone does not form a dimer, but O...O hydrogen bonds of 2.8 A link the molecules in a chain (Derry & Hamor, 1972). Very recently, we have measured the electronic spectra of the isolated 3-chlorotropolone (Tsuji, Sekiya, Nishimura, Mori & Takeshita, 1991) and 3-bromotropolone (Sekiya, Sasaki, Nishimura, Mori & Takeshita, 1990). The observation of tunnel splitting provides conclusive evidence for the de- localization of the proton. We have found that the hydroxylic proton is delocalized in 3-chlorotro- polone, whereas the proton is localized in 3- bromotropolone. It has been suggested that the localization of the hydroxylic proton strongly depends on the planarity of the molecule. In order to examine the effect of the substitution of a C1 atom on the molecular and crystal structure, an X-ray