Convex hulls of generalized moment curves

We consider the family of curves inR ⁴: {fx115-1}, wherep andq are positive integers, and determine the facial structure of the convex hull of these curves.     

High-resolution NMR spectroscopic trends and assignment rules of metal-free, metallated and substituted corroles

Major advances over the last few years have facilitated the synthesis of a large variety of meso-only substituted corroles that display interesting catalytic, therapeutic and photophysical properties. This work is the first to study extensively the NMR spectral characteristics of both metallated and non-metallated triarylcorroles in various organic solvents and provide guidelines for easy and reliable assignments of 1D 1H spectra from trends of J coupling constants and chemical shifts. An excellent correlation is found between C=C bond lengths derived from 3J(H,H) values and experimental lengths determined by x-ray crystallography of the same molecules. The nuclear Overhauser effect provides a robust 1D 1H NMR tool for determining the selectivity of electrophilic substitutions. Variable-temperature NMR and isotopic labelling reveal a single preferred tautomerization state and unsymmetric ring orientations at -70 degrees C. The beta-pyrrole protons demonstrate long-range heteronuclear couplings with the coordination core (15N) and with the ortho-19F nuclei of the meso-carbon aryl rings. In sum, application of multinuclear magnetic resonance to corroles and their metal complexes, through the compilation of chemical shifts and J couplings and the recognition of trends therein, provides basic information essential to reliable spectral assignments. Additionally, the conclusions drawn about the structures of corroles and the electron densities at various positions of the corrole macrocycle resulting from the application of high-resolution NMR techniques are of importance to an in-depth understanding of the molecular interactions and processes of this relatively new and rapidly expanding class of compounds.     

The chemistry of polycyclic arene imines. II. Photochemistry of phenanthrene 9,10-imine and of its N-butyl derivative

The uv irradiation of phenanthrene 9, 10-imine has been shown to give 9H-tetrabenzo[a, c, g, i]carbazole as the major photo-product both in argon purged acetone and in dichloromethane. Phenanthrazine, N-9-phenanthrenyl-9-phenanthrenamine and phenanthrene were formed in smaller quantities. 9-Phenanthrenamine was found to be a minor by-product. N-Butylphenanthrene 9, 10-imine yielded under similar conditions phenanthrene and N-butyl-9-phenanthrenamine as the only isolable polycyclic compounds. In the presence of air the substituted imine gave mainly 2-propylphenanthro[9, 10-d]oxazole.     

The effect of two isotopic species on the performance of an HX chemical laser

The influence of the presence of two isotopic on the performance of an HX chemical laser is investigated by means of a computer simulation of the system. The isotopic effect is shown to be important at low gas pressures and high threshold values, but of less importance for lasers operating under high output power conditions.     

Selective esterolysis of nitrophenyl acetates in crystalline α-cyclodextrin complexes

The esterolysis ofm-nitrophenyl acetate (mNPA) andp-nitrophenyl acetate (pNPA), complexed with -cyclodextrin, was investigated in the solid state. At 117 and 140°C, the initial half-times ofmNPA esterolysis were 30 and 24 h, respectively, whereasp NPA esterolysis was undetectably slow. At 117°C, themNPA reaction proceeded to completion, and cyclodextrin acetate andm-nitrophenol products were identified. At 140°C,the initial rate was followed by a slow phase with a half-time of 130 h, evidently due to a structural change in the complex. Themeta/para selectivity of the solid-state reaction is considerably enhanced over the selectivity reported in aqueous solution.     

Synthesis and structure of novel heterocyclic aminotelluranes

A series of novel 6-alkoxy-12H, 14H-[1,2,3]benzoxatellurazino[2,3-b]-[1,2,3]benzoxatellurazines 3 was synthesized from tetraalkoxytelluranes and bis(2-hydroxybenzyl)amines. ¹H, ¹³C and ¹²⁵Te NMR studies suggest that these aminotelluranes, unlike their orthoamidoester analogs, have a rigid trans-fused conformation. A preferential trans-fused conformation was also deduced from ab initio MO calculations of a model oxatellurazinooxatellurazine 7, using the STO-3G and SBK basis sets, and the Gaussian-92 program, which imply that the trans-fused aminotellurane is more stable than the corresponding cis isomer by 10.3 kcal/mol.     

Atmospheric pressure chemical ionization of alkanes,alkenes, and cycloalkanes

Normal and cyclic alkanes and alkenes form stable gas-phase ions in air at atmospheric pressure from 40 to 200°C when moisture is below 1 ppm. Ionization of alkanes in a ⁶³Ni source favored charge transfer over proton transfer through pathways involving [M?1]⁺ and [M?3]⁺ ions. Ion mobility spectra for alkanes showed sharp and symmetrical profiles while spectra for alkenes suggested fragmentation. Ion identifications were made by using mass spectrometry, and ionization pathways were supported by using deuterated analogs of alkanes and alkenes. Alkanes were ionized seemingly through a hydrogen abstraction pathway and did not proceed through an alkene intermediate. New methods for interpretation of mobility spectra utilizing ion mobility spectrometry, atmospheric pressure chemical ionization mass spectrometry, chemical ionization mass spectrometry, and ion mobility spectrometry-mass spectrometry data were demonstrated.     

Nitrogen atom transfer between manganese complexes of salen, porphyrin, and corrole and characterization of a (nitrido)manganese(VI) corrole

The investigations of complete nitrogen atom transfer reactions from (nitrido)manganese(V) salen to manganese(III) complexes of porphyrins and corroles revealed that stabilization of the [Mn(N)]2+ moiety is in the order of corrole > porphyrin > salen. The first kinetic examination of this quite fundamental reaction exposed a large solvent effect on both the enthalpy and entropy activation energies. Oxidation of the (nitrido)manganese(V) corroles leads to the first (nitrido)manganese(VI) complexes that are coordinated by tetrapyrrolic ligands.