Phosphorus-based combinatorial libraries: Use of amino acid derivatives as synthons

Summary Phosphorus has been used as a scaffold to prepare combinatorial libraries of phosphoramidates in which one of the diversity elements resulted from derivatives of amino acids. A small library was prepared for analytical and characterization purposes, followed by a larger library of approximately 8800 compounds. Libraries were assembled on solid supports using the conventional pool-and-divide method, followed by cleavage from the supports at the end of the synthesis. Mass spectrometry was used to confirm that library synthesis had been successful. Individual compounds were also prepared to study the stability of compounds of this type.     

The “invariance principle” in approximate molecular orbital theories

The widely used invariance “principle” of approximate MO theories is shown to be physically unreasonable and formally unnecessary. The use of ZDO-type schemes in an internally-defined orbital basis is proposed to replace this restrictive principle.     

Some comments on the counterpoise correction for the basis set superposition error at the correlated level

The use of the counterpoise method for the mitigation of basis set superposition error at the correlated level is discussed. Evidence is presented to show that the ghost basis plays a dual role in the counterpoise method: The orbitals of the system are improved by the ghost basis but at the expense of a nonphysical increase in the dimension of the virtual space. This second factor has no effect on application of the counterpoise method at the SCF level but it makes the use of the counterpoise method at the correlated level much less straightforward. © 1993 John Wiley & Sons, Inc.     

Optimal Batching in a Semi-Automated Order Picking System

As the materials handling revolution continues, the techniques of Management Science are finding more and varied application in the design and operation of production and distribution systems. This paper discusses the use of these techniques to batch orders in a semi-automated order-picking system of a Canadian provincial liquor board. The problem is formulated as a mixed-integer programming problem with the objective of arranging orders into batches so that the processing time is minimised. A sample problem is presented and solved, and computational aspects are discussed. Other possible application areas are outlined.     

Behaviour of six sulphided iron hydroliquefaction catalysts

Five iron ore samples and a synthetic magnetite were added to Wandoan bituminous coal as hydroliquefaction catalysts. Catalyst transformations after sulphiding and after subsequent hydrogenation were analysed. The conversion efficiency increased with decreasing particle size or increased crystallographic disorder and showed that different catalytic mechanisms operate in the hydroliquefaction of brown and black coals.     

Molecular force field and structure of water: Recent microwave results

Recently, microwave studies of the rotational spectra of water and its various isotopic species have been reported. These studies provide rotational constants and among others the quartic distortion constants, which depend on the quadratic part of the vibrational potential function. These data are collected and discussed, and the molecular force field and structure of water is considered in light of this recent microwave data. The quartic distortion data gives force constants which are very reasonable considering the difficulties in the distortion analysis of these light molecules, where as many as 22 parameters are being evaluated to fit the observed spectrum. The infrared and microwave data are combined within the theoretical framework of the small oscillations model and the results compare favorably with the true harmonic force field. The infrared and microwave valence bond force constants of H₂O are (mdyn/Å):

$\text{?}{}_{\mathrm{r}}\text{=7.746, ?}{}_{\mathrm{\theta }}\text{=0.700, ?}{}_{\mathrm{rr}}\text{=?0.093, ?}{}_{\mathrm{r\theta }}\text{=0.379}$

The results further confirm the usefulness of rotation-vibration data in the determination of force constans, and show that even for water with extremely large anharmonicity effects, a very representative force field can be obtained by combining ground state infrared and microwave data.Various molecular structures have been evaluated, and the average structures in the ground vibrational state for H₂O, D₂O and T₂O are found to be:

$\text{〈r〉}\text{〈θ}\text{O-H=0.9724}\text{A}\text{?}\text{HOH=104.50°}\text{O-D=0.9687}\text{A}\text{?}\text{DOD=104.35°}\text{O-T=0.9671}\text{A}\text{?}\text{TOT=104.26°}$

A one-dimensional approximation to the anharmonicity effects is applied to determine the equilibrium molecular structure of H₂O from the average structure data. The result is as follows:

$\text{r}{}_{\mathrm{e}}\text{=0.9587}\text{A}\text{?}\text{and θ}{}_{\mathrm{e}}\text{=103.9°}$

     

Formation of fluoro-meisenheimer complexes using homogeneous and heterogeneous fluoride ion sources

1-Chloro-2,4-dinitrobenzene, 1-fluoro-2,4-dinitrobenzene and 1,3-dinitrobenzene form Meisenheimer complexes with tetra-n-butylammonium fluoride and alumina supported alkali metal fluorides. Both kinetically controlled and thermodynamically controlled complexes are observed.