Combined Alkali‐Organoammonium Structure Direction of High‐Charge‐Density Heteroatom‐Containing Aluminophosphate Molecular Sieves

The charge density mismatch concept was applied to the synthesis of high‐charge‐density silicoaluminophosphate SAPO‐69 (OFF) and SAPO‐79 (ERI) and zincoaluminophosphate PST‐16 (CGS), PST‐17 (BPH), PST‐19 (SBS), and ZnAPO‐88 (MER) molecular sieves. Combined alkali‐organoammonium structure direction in these systems is thus enabled. Structure direction is treated from the perspective of stabilizing an ionic framework, the relationships between reaction charge density (OH^?/H₃PO₄), alkali and organoammonium content, and ionicity of tetrahedral framework atoms in successful structure direction are presented.     

Comparing Classes of Finite Structures

We compare classes of structures using the notion of a computable embedding, which is a partial order on the classes of structures. Our attention is mainly, but not exclusively, focused on classes of finite structures. Also, a number of problems are formulated.     

A mathematical description of the acoustic coupling of the mass/spring model

This paper describes hybrid mathematical model which couples the mechanics of the mass/spring model to the acoustic wave propagation model for use in generating the acoustic signal emitted by complex structures of paper fibres under strain. A discussion of the coupling method is presented including remarks on the errors encountered intrinsic to the discretisation scheme. The numerical results of a vibrating rubber band and a vibrating paper fibre are compared to their experimental counterparts. The fundamental frequencies of the acoustic signals are compared showing a close agreement between the experimental and numerical results.     

Cleavage of MEM ethers by tetrahalozincate reagents

A modification of the zinc halide-mediated removal of the MEM group is described. By the expedient of adding two molar equivalents of etheral hydrogen chloride or of lithium halide, the method is extended to substrates which otherwise chelate the zinc reagent without undergoing deprotection. The compatibility of the resulting reagent systems with other functional groups is demonstrated, and examples are presented where deprotection of mono-MEM-protecteed 1,2- and 1,3-diols can be carried out, avoiding the cyclisation which occurs normally.     

Synthesis of meta- and paracyclophanes containing unsaturated amino acid residues

[7.7], [8.8], [9.9] and [13.13] Paracyclophanes and [9.9] and [13.13] metacyclophanes containing two unsaturated amino acid residues have been synthesised. An X-ray crystallographic study of three of the paracyclophanes and molecular modelling of two paracyclophanes and two metacyclophanes revealed two main structural types. The ‘staggered’ structure appears to be favoured by longer hydrocarbon chains, whilst the ‘barrel’ structure appears to be more accessible to compounds containing shorter hydrocarbon chains. The [9.9] paracyclophane has been hydrogenated and deprotected to give a saturated amino acid, and an alternative approach to key aldehydes is reported.     

Recursive Structures and Ershov's Hierarchy

Ash and Nerode [2] gave natural definability conditions under which a relation is intrinsically r. e. Here we generalize this to arbitrary levels in Ershov's hierarchy of Δ sets, giving conditions under which a relation is intrinsically α-r. e. Mathematics Subject Classification: 03C57, 03D55.     

Phosphorus NMR Characterisation of P–N Bond Rotamers of a α‐P4S3 Amide with a Conformationally Constrained Chiral Substituent

Reactions of bicyclic α‐P₄S₃I₂ with Hpthiq gave solutions containing α‐P₄S₃(pthiq)I and α‐P₄S₃(pthiq)₂, where Hpthiq is the conformationally constrained chiral secondary amine 1‐phenyl‐1,2,3,4‐tetrahydroisoquinoline. The expected diastereomers have been characterised by complete analysis of their ³¹P{¹H} NMR spectra. Hindered P–N bond rotation in the amide iodide α‐P₄S₃(pthiq)I caused greater broadening of peaks in the room‐temperature spectrum of one diastereomer than in that of the other. At 183 K, spectra of two P–N bond rotamers for each diastereomer were observed and analysed. The minor rotamers showed strong evidence for steric crowding, having large diastereomeric differences in ¹J(P–P) and ²J(P–S–P) couplings (49 Hz, 16 % of value, and 4.4 Hz, 19 % of value, respectively).