The lattice vibrations of CeD2.12

The complete phonon dispersion relation including both optic and acoustic modes has been measured along the major symmetry axes of a single crystal of CeD_2.12 at 295 K by coherent neutron scattering. The results show the inadequacy of simple models previously used for the analysis of neutron incoherent scattering studies of rare earth dihydrides. The interstitial mode of vibration due to the excess deuterium (above CeD₂ in octahedral sites has also been observed.     

Polycyclic biphenylenes : Part V. The pmr spectra of annelated biphenylenes

The proton magnetic resonance spectra of a number of annelated biphenylenes are given. The influences of ring currents and bond-localisation effects are demonstrated.     

The application of molecular modelling to the interpretation of inverse gas chromatography data

The use of molecular modelling in the interpretation of inverse gas chromatography data is discussed. Crystal faces can be visualised and likely cleavage planes calculated using the surface attachment energies. Assuming that the preferred cleavage plane is the crystal face with the smallest attachment energy then the predominant crystal faces of a crystalline particle can be predicted. Surface adsorption can be modelled using Van der Waals and electrostatic interactions to evaluate the interaction energies between individual atoms of the probe molecule and atoms of the test molecule orientated as in the surface. Using examples of pharmaceutical materials, modelling has been shown to be successful in the understanding of changes in the surface energetics.     

Photoénolisation-IX: Stéréospecificitéet régiospécificitéde la réaction de diels-alder avec les photodiénols issus de la méthyl-2 et de la diméthyl-2,

2-Methyl- and 2,4-dimethylbenzophenone were irradiated with the unsymetrical dienophiles methyl acrylate, acrylonitrile, methyl methacrylate and methyl propiolate. The dienols additions proceed regiospecifically yielding in each instance a single hydroxylic compound having the car?ylate or the carbonitrile group in vicinal position. Syntheses of 1,2,3,4-tetrahydro- and 1,4-dihydronaphthols with various substituents were thus achieved. 3,4-Dihydronaphthalenes and naphthalenes were also obtained by dehydration. 2,4-dimethylbenzophenone was irradiated with acetylenedicarbonitrile yielding the dehydrated addition product 6-methyl 1-phenylnaphthalene-2,3-dicarbonitrile.     

Interlaboratory comparison of methods for the determination of incurred tilmicosin residues in bovine liver

The objective of this study was to compare 2 methods for the determination of tilmicosin residues in bovine liver samples. Three laboratories participated in the comparison of the 2 methods. The first method was described in a New Animal Drug Application (NADA 140-929), and the second was a modification of that method in which hexane was substituted for carbon tetrachloride in one cleanup step. Each of the 3 laboratories analyzed subsamples of 10 bovine livers containing incurred tilmicosin. Residues ranged from 2.3 to 81 ppm tilmicosin in the 10 liver samples with an 11.8% relative standard deviation obtained by using both methods. In addition, fortified-control liver tissue samples were analyzed concurrently with tissues containing incurred residues by using the modified method in one of the laboratories. The fortification levels ranged from 0.3 to 112 ppm, with recoveries ranging from 76 to 92%. The results from the 3 laboratories were comparable, indicating that the modified method was not only as effective as the original NADA method, but also more desirable because of the change to a less hazardous solvent.     

Mechanism of methoxide ion substitution in the z and e isomers of o-methylbenzohydroximoyl halides

Kinetics and stereochemical studies have been carried out on the reactions of the Z and E isomers of O-methylbenzohydroximoyl halides [1Z and 1E, ArC(X)=NOCH(3)] with sodium methoxide in 9:1 DMSO-methanol. The reactions of methoxide ion with hydroximoyl fluorides (X = F) are stereospecific. The reaction with 1Z (X = F) gives only the Z substitution product (1Z, X =OCH(3)). The reaction of methoxide ion with 1E (X = F) is less selective, giving ca. 85% E substitution product. The Hammett rho-values for the Z and E isomers (X = F) are +2.94 and +3.30, respectively. The element effects for 1Z (Ar = C(6)H(5)) are 2.21 (X = Br):1.00 (X = Cl):79.7 (X = F). The 1E element effects are (Ar = C(6)H(5)) 1.00 (X = Cl):18.3 (X = F) and (Ar = 4-CH(3)OC(6)H(4)) 1.97 (X = Br):1.00 (X = Cl):12.1 (X = F). The entropies of activation for these reactions are negative (for example, DeltaS() = -15 eu for 1Z and DeltaS() = -14 eu for 1E, Ar = 4-CH(3)OC(6)H(4), X = F). These experimental observations are consistent with a mechanism proceeding through a tetrahedral intermediate. Ab initio calculations were carried out to help explain the stereospecificity of these reactions. These calculations indicate that the tetrahedral intermediate from the Z isomer undergoes rapid elimination to the Z substitution product before stereomutation can take place. These calculations also show that the lowest barrier for rotation around the carbon-nitrogen single bond in the tetrahedral intermediate derived from 1E leads to an intermediate that eliminates fluoride ion to give E product.     

The α-arylation of derivatives of malonic acid with aryllead triacetates. New syntheses of ibuprofen and phenobarbital.

Derivatives of Meldrum's acid and the sodium salts of substituted malonic esters undergo rapid arylation in high yield when treated with aryllead triacetates. These reactions have been applied to the synthesis of ibuprofen, an analgesic, and in a closely related reaction 5-ethylbarbituric acid has been reacted with phenyllead triacetate to give phenobarbital.