Hyperfine interactions in the microwave spectrum of 2-propen-1-Imine (vinylimine)

A high resolution study of the microwave spectrum of 2-propen-1-imine has yielded values for ¹⁴N hyperfine coupling constants for both the trans-syn and trans-anti isomers. In the latter case, evidence was found for magnetic spin-rotation interaction. Rotational and centrifugal distortion constants of improved accuracy have been derived in the course of the analysis.     

The high-resolution microwave spectrum of cyclopropyl cyanide

The quadrupole hyperfine structure of six selected rotational transitions of cyclopropyl cyanide has been analyzed. The derived coupling constants are χ_aa = ?3.453(11) MHz and χ_bb = 1.759(16) MHz. The analysis yielded improved center frequencies for the multiplets and, in turn, led to slightly revised rotational constants: A = 15786.068(22), B = 3465.112(7), C = 3286.252(10) MHz; D_N = 1.18(30) kHz.     

Power requirement for the mixing of thixotropic liquids

A procedure has recently been proposed by Godfrey et al. [1] for the calculation of the variation of power consumption with time when a thixotropic liquid is agitated from rest using an impeller which rotates at constant speed. This procedure requires a knowledge of the power requirement for Newtonian and time-independent non-Newtonian liquids together with viscometric data for the thixotropic liquid obtained under constant shear rate conditions.Experimental work to test the procedure has been carried out in a 0.126-m-diameter cylindrical vessel with anchor, helical ribbon and helical screw impellers. Power consumption data were obtained for a range of Newtonian and time-independent non-Newtonian liquids and this was then used to make predictions of the measured power input to the thixotropic liquids: salad cream, tomato ketchup, yoghurt, paint and Laponite solutions.The agreement between experiment and theory was usually better than 10%. However, for the case of the helical screws rotating in Laponite it was observed that regions existed close to the vessel wall where there was no fluid circulation. In such cases, the predicted power input was greatly in excess of the measured value. This is not a serious limitation of the predictive procedure since efficient industrial mixers would keep the entire fluid in circulation.     

A crystallographic, EPR and theoretical study of the Jahn-Teller distortion in [CuTp2] (Tp- = tris[pyrazol-1-yl]hydridoborate)

Crystals of the title compound (1) contain two independent, centrosymmetric half-molecules per asymmetric unit. While both of these show Jahn-Teller elongated six-coordinate geometries, the lengths of the elongated Cu-N bonds in the two molecules differ by 0.117(2) A at 30 K. The structure of one of these molecules (molecule A) does not vary with temperature below 350 K. The other molecule (molecule B) shows Cu-N bond lengths that are temperature-dependent between 225 and 375 K, but do not vary further at lower temperature. This indicates a fluxional axis of Jahn-Teller elongation in this molecule at these higher temperatures. Consideration of the thermal parameters in these structures implies that the fluxionality in molecule B is frozen out near 150 K. This conclusion is supported by a Q-band powder EPR study. The d-d transition energies of molecules A and B have been calculated by several density function (DF) methods, including a time-dependent DF calculation. The crystallographic data have been reproduced using the vibronic coupling model of Burgi and Hitchman. This has shown that the different fluxionality regimes for molecules A and B are not a consequence of their different static molecular structures, but rather reflect their different local environments in the crystal.     

Crystal engineering of microporous 'Chinese-lantern' compounds to improve their ability to reversibly adsorb sulfur dioxide

Three new 'Chinese lantern' complexes [XMn(mu-dppO2)4MnX](2+)2X-.4MeOH.Me2CO [X = Cl, Br, I; dppO2 = 1,3-bis(diphenylphosphinoyl)propane], have been structurally characterised using single-crystal X-ray diffraction and shown to have increasing affinity for SO2 across the series Cl < Br < I via thermogravimetric measurements.     

An evolutionary approach for finding optimal trees in undirected networks

In many utilities, such as water and gas, materials are distributed through networks of pipes. For efficiency, many such distribution networks are constructed as trees. The cost of construction and operation of these is generally a complex function of the edges which are used, so that it is impossible to use conventional algorithms for the optimisation of trees. This paper presents a method for identifying a tree which is close to optimal. This evolutionary method is based on ideas from genetic algorithms.     

The preparation of (-)-grandisine B from (+)-grandisine D; a biomimetic total synthesis or formation of an isolation artefact?

An efficient new alkyne-acetal cyclization procedure has been developed to prepare enantiopure indolizidine building blocks from l-proline and then applied to prepare the Elaeocarpus-derived alkaloids grandisine B and grandisine D in an efficient manner. However, evidence is presented which indicates that grandisine B does not occur naturally but is formed by reaction of grandisine D with ammonia during the extraction/purification process.     

Synthesis of indenoporphyrins, highly modified porphyrins with reduced diatropic characteristics

Indene-fused porphyrins have been synthesized starting from 2-indanone. Knorr-type reaction of oximes derived from benzyl or tert-butyl acetoacetate with 2-indanone and zinc dust in propionic acid gave good yields of indenopyrroles. Treatment with N-chlorosuccinimide then gave 8-chloro derivatives, and these reacted with 5-unsubstituted pyrroles to give dipyrroles incorporating the fused indene unit. Hydrogenolysis of the benzyl ester protective groups afforded the related dicarboxylic acids, but condensation with a dipyrrylmethane dialdehyde under MacDonald "2 + 2" reaction conditions gave poor yields of the targeted indenoporphyrins. However, when an indene-fused dipyrrole was converted into the corresponding dialdehyde with TFA-trimethyl orthoformate and then reacted with a dipyrrylmethane dicarboxylic acid, an indenoporphyrin was isolated in 26% yield. The porphyrin gave a highly modified UV-vis absorption spectrum with three strong bands showing up in the Soret region and a series of Q bands that extended beyond 700 nm. The proton NMR spectrum also showed a significantly reduced diamagnetic ring current where the meso-protons gave resonances near 9.3 ppm instead of typical porphyrin values of 10 ppm. Nickel(II), copper(II), and zinc complexes were also prepared, and these exhibited unusual UV-vis absorption spectra with bathochromically shifted Soret and Q absorptions. The diamagnetic nickel(II) and zinc complexes also showed reduced diatropic character compared to typical nickel(II) and zinc porphyrins.