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Matrix Isolation (matrix + isolation)
Selected AbstractsMatrix isolation and magnetic parameters of septet 3,5-dicyanopyridyl-2,4,6-trinitreneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2010Sergei V. Chapyshev Abstract Septet 3,5-dicyanopyridyl-2,4,6-trinitrene was synthesized together with quintet 2-azido-3,5-dicyanopyridyl-4,6-dinitrene, quintet 4-azido-3,5-dicyanopyridyl-2,6-dinitrene, triplet 2,6-diazido-3,5-dicyanopyridyl-4-nitrene, and triplet 2,4-diazido-3,5-dicyanopyridyl-6-nitrene by photolysis of 2,4,6-triazido-3,5-dicyanopyridine in solid argon at 4,K. The electronic and magnetic properties of the matrix-isolated nitrenes were studied using electron paramagnetic resonance (EPR) spectroscopy in combination with density functional theory (DFT) calculations. The fine-structure parameters of the nitrenes were determined with high accuracy from spectral simulations. All signals in the EPR spectra of the nitrenes, randomly oriented in the solid phase, were unambiguously assigned based on eigenfield calculations of the Zeeman energy levels and angular dependences of resonance fields. Copyright © 2009 John Wiley & Sons, Ltd. [source] Direct chiral analysis of primary amine drugs in human urine by single drop microextraction in-line coupled to CEELECTROPHORESIS, Issue 16 2009Kihwan Choi Abstract Three-phase single drop microextraction (SDME) was in-line coupled to chiral CE of weakly basic amine compounds including amphetamine. SDME was used for the matrix isolation and sample preconcentration in order to directly analyze urine samples with the minimal pretreatment of adding NaOH. A small drop of an acidic aqueous acceptor phase covered with a thin layer of octanol was formed at the tip of a capillary by simple manipulation of the liquid handling functions of a commercial CE instrument. While the saline matrix of the urine sample was blocked by the octanol layer, the basic analytes in a basic aqueous donor phase were concentrated into the acidic acceptor drop through the octanol layer by the driving force of the pH difference between the two aqueous phases. The enantiomers of the enriched amines were resolved by using (+)-(18-crown-6)-tetracarboxylic acid as a chiral selector for the subsequent CE separation. From 10,min SDME with the agitation of the donor phase by a small stirrer retrofit to the CE instrument, enrichment factors were about a 1000-fold, yielding the LOD of 0.5,ng/mL for amphetamine. This low LOD value as well as the convenience of in-line coupled SDME make the proposed scheme well suited for the demanding chiral analysis of amphetamine-type stimulants. [source] The Low-temperature Photochemistry of s - cis Acyclic 1,3-Dienes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2002Michael Squillacote ABSTRACT In this article we have examined the very low-temperature photochemistry of three acyclic 1,3-dienes. We have used high-temperature deposition techniques combined with matrix isolation to create samples enriched with the thermally meta-stable s - cis form. This technique has allowed us to examine the separate photochemistry of the s - cis and s - trans conformers. Our results suggest the presence and the absence of barriers on the excited-state surface. In particular, we have found that the electrocyclic closure and s - cis,s - trans photochemical isomerization stops at 15 K for 2,3-dimethyl-1,3-butadiene-d10. The closure occurs at higher temperatures in solution but is slowed by a deuterium isotope effect. The s - trans conformer of EE-2,4-hexadiene shows almost no photoreactivity in a matrix under 254 nm irradiation, but the s - cis conformer is rapidly converted to ZE-2,4-hexadiene (ZE-HXD). The photoreactivity of ZE-HXD is similar in that there is a relatively quick conversion of the s - cis conformer under these conditions, with only a very slow conversion of the s - trans to photoproducts. [source] Tamed Tigers: Stabilization of Reactive CarbenesCHEMPHYSCHEM, Issue 13 2008Martin Albrecht Prof. Taming wild carbenes: Following previous achievements in characterizing free carbenes,long considerered as curiosities and intermediates too reactive to be isolated,Schreiner and coworkers succeeded in stabilizing hydroxymethylene (see picture), the simplest of all oxycarbenes, by matrix isolation. This carbene gradually rearranges into its formaldehyde tautomer by a barrierless tunnelling process. [source] | |||||||||||||