Conformational study of cis-1,4-di-tert-butylcyclohexane by dynamic NMR spectroscopy and computational methods. Observation of chair and twist-boat conformations

[reaction: see text] Low-temperature 13C NMR spectra of cis-1,4-di-tert-butylcyclohexane (1) showed signals for the twist-boat (1a) and chair (1b) conformations. 13C NMR signals were assigned to specific carbons based on the different populations, different symmetries (time-averaged C(2v) for 1a and time-averaged C(s) for 1b), and calculated chemical shifts (GIAO, HF/6-311+G*). In addition to slow ring inversion and interconversion of the chair and twist-boat conformations, slow rotation of the tert-butyl groups was found. Most of the expected 13C peaks were observed. Free-energy barriers of 6.83 and 6.35 kcal/mol were found for interconversion of 1a (major) and 1b (minor) at -148.1 degrees C. Conformational space was searched with Allinger's MM3 and MM4 programs, and free energies were obtained for several low-energy conformations 1a-c. Calculations were repeated with ab initio methods up to the HF/6-311+G* level. Molecular symmetries, relative free energies, relative enthalpies and entropies, frequencies, and NMR chemical shifts were obtained. A boat conformation (1d; C(2v) symmetry) was generated and optimized as a transition state by ab initio, MM3, and MM4 calculations.     

Analysis of dynamic mixed mode stress fields in bimaterials by the method of caustics

The equations of caustics for dynamically extending curvilinear interface cracks are derived where optical isotropy and anisotropy of the material have been considered, respectively. The equations have been obtained by applying the method of generalized complex potentials. Moreover, an algorithm for the determination of stress intensity factors from experimentally obtained caustics is presented for the case of dynamic crack extension.     

Fringes demodulation in time-averaged digital shearography using genetic algorithms

This paper presents a phase recovery method, based on genetic algorithms, in time-average shearography. It is proved that a single Bessel fringe pattern obtained under a subtraction operation could be enough to calculate the phase. A merit function is solved iteratively using genetic operator like selection, reproduction and mutation. Experimental results are presented in this paper using a simple shearing system based on a Fresnel biprism.     

Cyclopentadecanone 2,4‐dinitrophenylhydrazone

In the title compound, C₂₁H₃₂N₄O₄, no disorder is present in the 15‐membered hydrocarbon ring, which exists in an unsymmetrical quinquangular [12345] conformation. The 2,4‐dinitrophenylhydrazone group is approximately perpendicular to the C₁₅ ring, with a dihedral angle of 84.66 (1)° between their best planes.     

N-nitrosoamide-mediated N --> O nitroso transfer to alcohols with subsequent denitroxylation

Decomposition of certain N-benzyl-N-nitrosoamides is often accompanied by small amounts of benzaldehyde whose formation was postulated to arise from in situ formation and oxidation of benzyl alcohol. Incubation of excess benzyl alcohol with thermostable N-benzyl-N-nitrosoamides at ambient temperatures in inert solvents generates benzyl nitrite, N-benzyl amides, and benzaldehyde as the major products. Benzyl nitrite formation appears to be linked to N --> O nitroso transfer between the N-benzyl-N-nitrosoamides and benzyl alcohol, which is subject to the previously observed electronic and steric features of the acyl substituent although the former appears to play a much larger role than the latter. Benzaldehyde formation evidently arises from dehydronitrosation (denitroxylation) of the nitrite via O-N bond homolysis and H-abstraction from the resultant benzyloxy radical. Although trans-nitrosation occurs with methanol, 1 degree, 2 degree, and 3 degree alcohols, the reaction is evidently subject to steric effects at both the alpha and beta carbons of the alcohol. Additionally, carbonyl formation only occurs with 2 degrees alcohols and those that can derive resonance-stabilized carbonyls.     

Towards validating a method for two-dimensional electrophoresis/silver staining

Two-dimensional electrophoresis (2-DE) is a technique involving numerous steps, many of them to be performed manually. Hence, some operator dependency must be taken into account. An attempt to elucidate the reliability of 2-DE combined with silver staining is presented, employing the general practice to validate a method in pharmaceutical analysis. Most proteomic studies employing 2-DE aim at qualitative or quantitative differences in protein expression. One of the most sensitive and broadly applied staining techniques is silver staining. In order to gain information on accuracy, precision, linearity, and ruggedness of this technique, gels were run in replicates with different amounts of protein from a complex standard sample. In addition, sets of gels were repeated by two different operators in a second independent laboratory equipped with identical hardware and software. Our results show that reliable qualitative data on differential protein expression can be obtained by 2-DE, nevertheless replicate gels should be run and experimental conditions have to be kept stringently to a standardized protocol. Quantitative data are just achievable with spots, which are well-resolved, of high quality, with an optical density (OD) above a certain threshold (OD > 10), and which show a linear response. Quantitative differences occurring due to method-derived deviations may easily be misinterpreted as true changes in protein expression. After normalization, relative standard deviation (RSD) values of approximately 30% (n = 4) could be obtained, therefore minor changes (< 50%) should be critically reviewed.     

Pheromone, 2. Mitt. Ein Verfahren zur Herstellung von Ketonen und Spiroketalen durch Entschwefelung von Thienylethern

Summary Starting from substituted methoxythiophenes1 ketones and spiroketals can be synthesized in one step by desulfurization with partial hydrogenation. The bark beetle pheromone chalcogran2 a and the wasp anti aggression pheromone2 b were prepared by this method.

Prof. Dr. F. Sauter zum 60. Geburtstag gewidmet     

Alkali metal chelation by diacetamide

Proton NMR spectroscopy indicates that diacetamide exists as an equilibrium mixture of Z,Z and E,Z diastereomers in methanol solution. Addition of Lil, Na1 or K1 (configurational titration) shifts the quilibrium because of bidentate complexation (chelation) by the amide carbonyl oxygens.