Showing papers by "Hiroshi Sekiya published in 1991"

Electronic spectra of jet‐cooled 3‐chlorotropolone. Proton tunneling in the S1 state

Abstract: The electronic spectra have been measured for jet‐cooled 3‐chlorotropolone in the S1–S0 region to investigate the effect of an asymmetric substitution on proton tunneling in tropolone. Both the 0++ and 0−− transitions have been identified in the fluorescence excitation spectrum, while no 0−+ or 0+− transition has been detected. This suggests that the double minimum potential energy function is almost symmetric for both S1 and S0. The tunneling doublet separations for the origin bands of 3‐chlorotropolone and its OD derivative have been measured to be 23 and 3 cm−1, respectively. These values are very similar to the corresponding values of 19 and 2 cm−1 for tropolone and its OD derivative, indicating that the substitution of a chlorine atom influences only a little on the strength of the intramolecular hydrogen bond.

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

Electronic spectrum of jet-cooled tropolone-3-d.

Abstract: The laser fluorescence excitation spectrum of jet-cooled tropolone-3-d has been measured to investigate the effect of an unsymmetrical substitution of a deuterium on proton tunneling and the equilibrium geometry.