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Reactivity Difference (reactivity + difference)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

One-Step Preparation of Coaxial CdS,ZnS and Cd1,xZnxS,ZnS Nanowires,

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2005
Y.-J. Hsu
Abstract Preparation of coaxial (core,shell) CdS,ZnS and Cd1,xZnxS,ZnS nanowires has been achieved via a one-step metal,organic chemical vapor deposition (MOCVD) process with co-fed single-source precursors of CdS and ZnS. Single-source precursors of CdS and ZnS of sufficient reactivity difference were prepared and paired up to form coaxial nanostructures in a one-step process. The sequential growth of ZnS on CdS nanowires was also conducted to demonstrate the necessity and advantages of the precursor co-feeding practice for the formation of well-defined coaxial nanostructures. The coaxial nanostructure was characterized and confirmed by high-resolution transmission electron microscopy and corresponding energy dispersive X-ray spectrometry analyses. The photoluminescence efficiencies of the resulting coaxial CdS,ZnS and Cd1,xZnxS,ZnS nanowires were significantly enhanced compared to those of the plain CdS and plain Cd1,xZnxS nanowires, respectively, owing to the effective passivation of the surface electronic states of the core materials by the ZnS shell. [source]

Quantitatively resolving mixtures of isobaric compounds using chemical ionization mass spectrometry by modulating the reactant ion composition

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2008
E. C. Fortner
Acrolein (C3H4O) and 1-butene (C4H8) can both be individually detected by proton transfer chemical ionization mass spectrometry (CI-MS). However, because these compounds are isobaric, mixtures of these two compounds cannot be resolved since both compounds react with H3O+ via a proton-transfer reaction to form a protonated molecule that is detected at a nominal mass-to-charge ratio of 57 (m/z 57). While both compounds react with H3O+ only acrolein reacts to any significant extent with H3O+(H2O). Recognizing that the electrical potential applied to a drift tube reaction mass spectrometer provides a simple and effective means for varying the relative intensity of the H3O+ and H3O+(H2O) reactant ions we have developed a method whereby we make use of this reactivity difference to resolve mixtures of these two compounds. We demonstrate a technique where the individual contributions of acrolein and 1-butene within a mixture can be quantitatively resolved by systematically changing the reagent ion from H3O+ to H3O+(H2O) through control of the electric potential applied to the drift tube reaction region of a proton transfer reaction mass spectrometer. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Chemical Protein Synthesis by Kinetically Controlled Ligation of Peptide O-Esters

CHEMBIOCHEM, Issue 4 2010
Ji-Shen Zheng
Designer peptides: A large reactivity difference was observed between two peptide O-esters that can undergo peptide ligation through an in situ O-to-S acyl shift. This observation allowed for the design of "one-pot" N-to-C sequential peptide fragment condensation through kinetically controlled ligation with more readily accessible peptide O-esters. [source]

Computational study of the synthesis of benzoin derivatives from benzil

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2006
Kevser Göçmen Topal
Abstract Benzil (1,2-diphenylethane-1,2-dione) undergoes cyanide catalyzed condensation with benzaldehyde to yield O -benzoylated benzoin (2-benzoyl-1,2-diphenylethanone). In this study, the experimentally suggested mechanism has been modeled with PM3 and verified with B3LYP. The effect of the substituent on the reaction yield has been rationalized by considering two benzil derivatives; 1,2-bis(2-chlorophenyl)ethane-1,2-dione and 1,2-bis(2-fluorophenyl)ethane-1,2-dione and three benzaldehyde derivatives; o -fluorobenzaldehyde, o -methylbenzaldehyde and 2-pyridinecarboxaldehyde. The effect of the solvent has been modeled by using the isodensity-surface polarizable continuum (IPCM) model. Reactivity descriptors have been used to justify the reactivity differences of the various substituents. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

Rhodium(I)-Catalysed Intramolecular [2+2+2] Cyclotrimerisations of 15-, 20- and 25-Membered Azamacrocycles: Experimental and Theoretical Mechanistic Studies

CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2009
Anna Dachs
Abstract Number of members makes a difference: The [2+2+2] intramolecular cyclotrimerisation of a new series of 20- and 25-membered azamacrocycles catalysed by the Wilkinson's catalyst are reported (see scheme). The 20- and 25-membered azamacrocycles show different reactivity. Why? Theoretical calculations give insight into the reactivity differences observed for the 20- and 25-membered macrocycles. A new series of 20- and 25-membered polyacetylenic azamacrocycles have been satisfactorily prepared and completely characterised by spectroscopic methods. Various [2+2+2] cyclotrimerisation processes catalysed by the Wilkinson's catalyst, [RhCl(PPh3)3], were tested in the above-mentioned macrocycles. The 25-membered azamacrocycle (like the previously synthesised 15-membered azamacrocyle) led to the expected cyclotrimerised compound in contrast to the 20-membered macrocycle, which is characterised by its lack of reactivity. The difference in reactivity of the 15-, 20- and 25-membered macrocycles has been rationalised through density functional theory calculations. S,ha sintetitzat i caracteritzat espectroscòpicament una nova sèrie de macrocicles nitrogenats poliacetilènics de 20- i 25-membres. Amb aquests macrocicles s'han dut a terme les reaccions de ciclotrimerització [2+2+2] catalitzades pel catalitzador de Wilkinson, [RhCl(PPh3)3]. El macrocicle nitrogenat de 25-membres (de la mateixa manera que el macrocicle nitrogenat de 15-membres) permet l,obtenció del compost ciclotrimeritzat. Per contra, el macrocicle de 20-membres es caracteritza per la seva falta de reactivitat. El diferent comportament de reactivitat dels macrocicles de 15-, 20-, i 25-membres ha estat estudiat mitjançant càlculs teòrics basats en la teoria del funcional de la densitat. [source]