Convenient synthesis of 12H-benzo[a]xanthenes from 2-tetralone

Convenient and facile syntheses of 12H-benzo[a]xanthenes from 2-tetralone and 2-hydroxyaromatic aldehydes is described. 2-Tetralone reacted with 2-hydroxyarylaldehydes to yield 12H-benzo[a]xanthenes under acidic conditions.     

k-ary monoids of term operations

Communicated by Norman R. Reilly     

Check Character Systems Using Chevalley Groups

We show that the Sylow 2-subgroups of nearly all Chevalley groups in even characteristic allow the definition of a check-character-system which detects all single and the most important double errors.     

ESR and optical spectroscopy of copper-doped PLZT electro-optic ceramics

2+ spectra in axial and cubic crystal fields. Cu²⁺ substitutes for Ti⁴⁺ and the excess charge can be compensated by La³⁺ on a nearest-neighbor site, thus creating axial symmetry. The centers of cubic symmetry are those where the charge is compensated in distant spheres. In contrast to pure PLZT, PLZT:Cu exhibits a new luminescence band peaking at 1.18 eV. This emission is ascribed to the ²T₂(D)→²E(D) transition of Cu²⁺(3d⁹) which can be excited either in the resonant 1.87 eV band or via charge-transfer excitation bands at 2.40, 2.57, and 3.03 eV. The absorption band at 1.45 eV is assumed to be that of Cu⁺ ions. Annealing in hydrogen and in oxygen atmospheres caused decrease and restoration, respectively, of the ESR and luminescence intensities as a consequence of Cu²⁺ conversion into Cu¹⁺ and vice versa. Received: 14 November 1997/Accepted: 8 December 1997     

Methyl reorientation in solid 3-ethylchrysene and 3-isopropylchrysene

We have measured the proton spin-lattice relaxation rate as a function of temperature in polycrystalline 3-ethylchrysene at nuclear magnetic resonance Larmor frequencies of 53.0 and 22.5 MHz and in polycrystalline 3-isopropylchrysene at 53.0, 22.5 and 8.50 MHz. The syntheses of these new compounds are presented. The relatively large chrysene backbone creates an ideal and unique environment for the alkyl groups such that methyl group rotation is the only motion on the nuclear magnetic resonance Larmor frequency timescale over a large temperature range. The relaxation rate data are interpreted in terms of the simplest possible dynamical model; that of random hopping for the methyl group(s), all of which are equivalent in the solid state. The barriers of 11–12 kJ mol⁻¹ are typical for methyl groups in ‘isolated' ethyl and isopropyl groups.     

A new emission of ZnS:Ni2+ arising from the 3T1(P) → 3T1(F) transition

A photoluminescence band with zero-phonon transitions at $\text{?}\text{= 12438 cm}{}^{-1}$ (this one subject to self-absorption) and at 12259 cm^-1 has been detected with ZnS:Ni crystals. Based on the appearance of these two lines, on the similarity of the whole spectrum with the ³T₂(F) → ³T₁(F) Ni²⁺ luminescence, and on preparation evidence, this new emission is interpreted as the ³T₁(P) → ³T₁(F) transition of substitutional Ni²⁺(3d⁸) ions in a tetrahedral crystal field.     

The Dehn Function of PSL2(Z[1/p])

We show that PSL₂(Z[1/p]) admits a combing with bounded asynchronous width, and use this combing to show that PSL₂(Z[1/p]) has an exponential Dehn function. As a corollary, PSL₂(Z[1/p]) has solvable word problem and is not an automatic group.