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Para Isomers (para + isomer)
Selected AbstractsSubstituent effect on local aromaticity in mono and di-substituted heterocyclic analogs of naphthaleneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2010Afshan Mohajeri Abstract A quantitative study on local aromaticity has been performed on a series of mono- and di-substituted biheterocycles (quinoline, isoquinoline, quinoxaline, quinazoline). Three electronically based indices (PDI, ATI, and FLU) have been employed to investigate the substituent effect on the , -electron delocalization in both heterocycle and benzenoid rings. Three typical substituents (Cl, OCH3, and CN) with different inductive and resonance power have been selected. Generally, substituent causes a reduction in aromaticity irrespective of whether it is electron attracting or electron donating. It is shown that the maximum aromaticity exhibits a similar trend of Cl,>,CN,>,OCH3 for all the studied rings. Moreover, it is found that the substituent situation with respect to the heteroatom has a significant influence on the aromaticity. It results from our study that in di-substituted derivatives, irrespective of whether the two substituents form a meta or para isomer, they preferably choose the position which leads to the maximum aromaticity character. Copyright © 2009 John Wiley & Sons, Ltd. [source] Functional [6]Pericyclynes: Aromatization to Substituted carbo -Benzenes,CHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2007Catherine Saccavini Dr. Abstract Reductive treatment of stereoisomeric mixtures of variously substituted hexaoxy[6]pericyclynes with SnCl2/HCl led to the corresponding substituted carbo -benzenes. Tetramethoxyhexaphenyl[6]pericylynediol and dimethoxyhexaphenyl[6]pericyclynetetrol thus proved to be alternative precursors of hexaphenyl- carbo -benzene, previously described. Another hexaaryl- carbo -benzenic chromophore with 4-pyridyl and 4-anisyl substituents was targeted for its second-order nonlinear optical properties and was obtained by aromatization of a dimethoxy[6]pericyclynetetrol. Two alkynyl substituents in para positions were also found to be compatible with the C18carbo -benzene ring, provided that the four remaining vertices are substituted by phenyl groups. In the protected series, bis(trimethylsilylethynyl)hexaphenyl- carbo -benzene (C18Ph4(CCTMS)2) could be isolated and fully characterized, even by X-ray crystallography. In the bis-terminal series, the diethynylhexaphenyl- carbo -benzene C18Ph4(CCH)2 could not be isolated in the pure form. It could, however, be generated by two different methods and identified by the corresponding 1H NMR spectra. Unsubstituted carbo -benzene C18H6 remains unknown, but tetraphenyl- carbo -benzenes C18Ph4H2 with two unsubstituted vertices proved to be viable molecules. Whereas the "para" isomer could be characterized by MS and 1H and 13C NMR spectroscopy only in a mixture with polymeric materials, the "ortho" isomer (with adjacent CH vertices) could be isolated, and its structure was determined by using X-ray crystallography. The structure calculated at the B3PW91/6-31G** level of theory turned out to be in excellent agreement with the experimental structure. The 1H and 13C NMR chemical shifts of hexa- and tetraphenyl- carbo -benzenes were also calculated at the B3LYP/6-31+G** level of theory and were found to correlate with experimental spectra. The remote NMR deshielding of peripheral protons (through up to five bonds) revealed a very strong diatropic circulation around the C18 ring, regardless of the substitution pattern. In full agreement with theoretical investigations, it has been demonstrated experimentally that the carbo -benzene ring is "independently" aromatic, in accord with structural,energetic and ,magnetic criteria. [source] Field-amplified sample injection-micellar electrokinetic capillary chromatography for the analysis of bisphenol A, bisphenol F, and their diglycidyl ethers and derivatives in canned soft drinksELECTROPHORESIS, Issue 9 2010Héctor Gallart-Ayala Abstract Conditions were established for the separation and analysis of bisphenol A, bisphenol F, and their diglycidyl ethers by micellar electrokinetic capillary chromatography (MECC). Good resolution was obtained for all compounds, although in order to achieve the separation of ortho,ortho, ortho,para, and para,para isomers of bisphenol F diglycidyl ether (BFDGE), BFDGE·2H2O and BFDGE·2HCl, it was necessary to use a 25,,m id fused silica capillary. To increase sensitivity, a field-amplified sample injection (FASI)-MECC method was developed using 10,mM SDS solution as injection matrix and a 75,,m id fused silica capillary. Instrumental quality parameters such as LODs (<55,,g/L with standards), linearity (r2>0.999), and run-to-run and day-to-day precisions (RSD values lower than 12.5%) were determined. Finally, the suitability of the FASI-MECC method for the analysis of bisphenol A, bisphenol F, and their diglycidyl ethers in canned soft drinks was evaluated. Quantitation was performed by matrix-matched calibration using a plastic-bottled isotonic drink as matrix. The results showed that FASI-MECC is an economic method for the screening and quantitation of these kinds of compounds in soft drink beverages, with no loss of reproducibility, and effective at concentrations lower than the specific migration level values established by the European Union. [source] Highly Efficient Halogenation of Organic Compounds with Halides Catalyzed by Cerium(III) Chloride Heptahydrate Using Hydrogen Peroxide as the Terminal Oxidant in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Habib Firouzabadi Abstract In this article a new environmentally friendly catalytic method is described for the efficient monoiodination and bromination of arenes and also iodoetherification and iodolactonization of olefins using hydrogen peroxide as the terminal oxidant. The method is based on using sodium iodide or sodium bromide, hydrogen peroxide (35%) and cerium(III) chloride as an effective catalyst in water at room temperature or under reflux conditions. By this protocol, iodination of anilines proceeded with high regioselectivity at the para position with the formation of small amounts of the ortho isomers. However, bromination of anilines proceeded with absolute regioselectivity to give the para isomers as the sole products in high yields. Iodinations and brominations of m -xylene, toluene, chloro- and bromobenzenes were proceeded with excellent regioselectivity to produce the para isomers as the sole products. Benzene was also halogenated by this catalytic system to give the monohalogenated benzene in good yields. Iodoetherification and iodolactonization of olefins also proceeded easily in high yields at room temperature. However, the bromination of olefins by this protocol failed and the starting materials were detected intact. [source] Vicarious nucleophilic amination of nitroquinolines by 1,1,1-trimethylhydrazinium iodideJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2008Maria Grzego The amination of 3-, 5-, 6-, 7- and 8-nitroquinoline via the vicarious nucleophilic substitution of hydrogen (VNS) with 1,1,1-trimethylhydrazinium iodide (TMHI) in the presence of t -BuOK in DMSO was studied. The amination occurs regioselectively giving ortho or ortho and para isomers relative to the nitro group with a high yield (95-86%). 2-Nitroquinoline does not undergo vicarious amination but displacement of the labile nitro group by an amino group occurs and then transformation to an imine compound and hydrolysis gives2(1H)-quinolinone. [source] | ||||||||||