A further investigation of the crystal structures of naphthazarin

Abstract

The crystal structures of two modifications of naphthazarin (formally 5,8,dihydroxy-l,4-naphthaquinone) have been further refined, using three-dimensional X-ray countel data in one case, and previously reported photographic data in the other. The carbon skeleton of the molecule is shown to possess Dah symmetry within the standard deviation in carbon--carbon bond length, which was 0.006 A in the more accurate study. The phenolic hydrogen atom, which is involved in an intramolecular hydrogen bond between the phenolic and quinonoid oxygen atoms, appea, s to be non-symmetrically placed between them. This structure can be interpreted in terms of resonance between the zwitterion contributors"

Polymorphism of maleic hydrazide. I

“…Indeed, one may assume that their occurrences are more frequent than would be expected from the random statistical distribution. Numerous examples exist of the same space group occurring for polymorphs or of closely related phenomena of phase transitions between two phases of the same symmetry (often described as isostructural or isosymmetric phase transitions): two of the polymorphs of dibenzoylmethane crystallize in space group Pbca (Etter et al, 1987;Hollander et al, 1973;Jones, 1976;Williams, 1966); both polymorphs and of resorcinol crystallize in space group Pna2 1 (Robertson & Ubbelohde, 1938); three polymorphs of naphthazarin, A, B and C, have the space group P2 1 ac (Pascard-Billy, 1962;Cradwick & Hall, 1971;Shiau et al, 1980;Herbstein et al, 1985); the white and yellow polymorphs of dimethyl 3,6-dichloro-2,5dihydroxytelphthalate are both P " 1 (Byrn et al, 1972); two polymorphs of 4,5-dichloro-3(2H)-pyridazinone occur in space group P2 1 ac (Lynch et al, 1985); two polymorphs of oxalic acid dihydrate crystallize in the equivalent space groups P2 1 ac and P2 1 aa (Coppens & Sabine, 1969). 1,3-Cyclohexanedione undergoes an isosymmetric transition within space group P2 1 ac (Katrusiak, 1990(Katrusiak, , 1991; similarly, P2 1 ac to P2 1 ac transitions occur in tin(II) chloride dihydrate (Kitahama & Kiriyama, 1977), dimethylaminobenzonitrile (Jameson et al, 1994) and in 6-hydroxy-4,4,5,7,8-pentamethyldihydrocoumarin (Budzianowski & Katrusiak, 2001), 1,2,4,5tetrabromobenzene and transform within P2 1 aa symmetry (Gafner & Herbstein, 1960;Gafner, 1964); a P2 1 2 1 2 1 to P2 1 2 1 2 1 transition occurs in oxitropium bromide (Zamir et al, 1993); KTiOPO 4 (KTP) undergoes a Pna2 1 to Pna2 1 phase transition (Allan et al, 1992).…”

1H and2H NMR Relaxation in Hydrogen-Bonded Solids Due to a Complex Motion: Classical Jumps over a Barrier and Incoherent Tunneling

“…temperature dependence for the separate reorientations Using the Skinner-Trommsdorff tunneling rate constant (jumps over the barrier and tunneling) is also shown in (Eq. [5]), it is clear that different calculations of the correlathese figures. At low temperatures the relaxation rates are tion function result in temperature dependencies of the secdominated by the tunneling motion and a flat T 1 temperature ond moment which differ dramatically.…”

“…The spectral density for the tunneling and jumps over the barrier are given by Eqs. complex motion is [1] to [5].…”

“…The angles u ikAB and interatomic distances R ikA and R ikB in Naphthazarin B were calculated for the separate ik spin pairs (5 …”

“…[99] [ 2 ] to [ 5 ] . If the internuclear distances change during the tunneling motion, It seems that the proper approach is to treat the separate [ 26 ] and [ 27 ] , respectively.…”