Contents of Volume 53

Volume Contents

Contents of Volume 53     

Transient free convection about a horizontal circular cylinder in a porous medium

The method of matched asymptotic expansions is employed for investigating the growth of the free convection boundary-layer on a horizontal circular cylinder which is embedded in a porous medium. It is assumed that the Rayleigh number is large, but finite, and the time of investigation is short. It is shown that the solution contains terms that are absent from the solution based on the boundary-layer approximation and that vortices form at both sides of the cylinder. The development of the plume region near the top of the cylinder, as well as the local and average Nusselt numbers, are evaluated and presented in graphical form.     

Reactivity of biologically important reduced pyridines. VIII. A semiempirical (AM1) study of the oxidation of 3-substituted-1-methyl-1,4-dihydropyridines

Significant linear correlations were observed between AM1-derived adiabatic, but not vertical, ionization potentials and the log of ferricyanide-mediated oxidation of 3-substituted-1-methyl-1,4-dihydropyridines. This result is consistent with a rate-determining electron loss in the reaction sequence and suggests molecular relaxation subsequent to the initial electron transfer. In addition, useful relationships were generated between oxidation rate and absolute electronegativity, a parameter derived from hard-soft acid-base theory.     

Mixed Convection on a Horizontal Surface Embedded in a Porous Medium: the Structure of a Singularity

The mixed convection boundary-layer flow on a horizontal impermeable surface embedded in a saturated porous medium and driven by a local heat source is considered. Similarity solutions are obtained for specific outer flow variations and these are shown to have a solution only for parameter values greater than some critical value. When this is not the case the solution develops a singularity at a finite distance from the leading edge. The nature of this singularity is also discussed.     

Magnetic properties of x • MnO • (1−x)[19TeO2 • PbO] glasses

The results of magnetic studies on x ? MnO ? (1 ? x)[19TeO₂ ? PbO] glasses are reported. The magnetic properties of these glasses are function of MnO content. For glasses with x > 5 mol% MnO, an antiferromagnetic behaviour is evidenced.     

Isomeric interconversions in tamoxifen and related compounds: An AM1 study

Semiempirical molecular orbital techniques (AM 1) were applied to the study of cis–trans isomerism in tamoxifen and related compounds. AM 1-derived structures were in good agreement with X-ray data. Theoretical evaluation indicated that both cis- and trans-tamoxifen as well as the 4-hydroxytamoxifen isomeric pair were very close in energy, confirming experimental results suggesting nearly equivalent populations of the two isomers under equilibrium conditions. Mechanistic studies included a determination of selected proton affinities to establish the nature and location of compound protonation as well as conformational studies of the formed carbocations. In particular, internal rotation about the incipient olefinic C? C bond in the tamoxifen and 4-hydroxytamoxifen carbocations provided a likely reaction mechanism. There evaluations suggested that the more rapid isomerization of 4-hydroxytamoxifen as compared to tamoxifen was related to transition-state stabilization through phenolic oxygen electron donation. © 1995 John Wiley & Sons, Inc.     

Reactions of nickelocene with methyl-, ethyl- and vinyl-lithium compounds. Hydrogen elimination and cyclopentadienyl ring hydrogenation

It has been shown that bis(cyclopentadienyl)(μ-cyclopentadiene)dinickel, (NiCP)₂(η-C₅H₆), and (η⁵-cyclopentadienyl) (η³-cyclopentenyl)nickel, CpNi(η³-C₅H₇), are formed in the reaction of nickelocene with methyl-lithium and with 1-phenyl-2-methyl-propenyl-lithium. The compound (NiCp)₂(μ-C₅H₆) can be only formed as a result of the reduction of the cyclopentadienyl ring bonded to the nickel atom whereas the formation of CpNi(η³-C₅H₇) can be explained by the further hydrogeneration of cyclopentadiene formed in the earlier reaction steps. (NiCp)₂(μ-C₅H₆) has been fully characterised spectrometrically and its X-ray structure determined. It crystallises in the orthorhombic system, space group Pnma, with four molecules per unit cell.     

Boundary Layer Flow over a Continuously Moving Thin Needle in a Parallel Free Stream

We investigate the boundary-layer flow on a moving isothermal thin needle parallel to a moving stream. The governing equations are solved numerically by a finite-difference method. Dual solutions are found to exist when the needle and the free stream move in the opposite directions.