Search results for "solvent effect"

MÖSSBAUER EFFECT STUDY ON THE HIGH-SPIN (5T2) ⇌ LOW SPIN (1A1) TRANSITION IN [Fe(2-pic)3]Cl2. DILUTION EFFECT IN [FexZn1-x(2-pic)3] Cl2. EtOH AND CRY…

1976

The domino reaction between 4,6-dinitrobenzofuroxan and cyclopentadiene. Insights on the nature of the molecular mechanism

2004

Abstract The molecular mechanism of the domino reaction between 4,6-dinitrobenzofuroxan, 1 , and cyclopentadiene, Cp, to give the adduct 11 is examined through density functional theory (DFT) calculations at B3LYP/6-31G* level. This domino reaction comprises two consecutive formally [4+2] cycloadditions. The first one is a two-center addition initialized by the nucleophilic attack of Cp to the more electrophilic center of 1 . The subsequent cyclization can take place along two competitive channels associated to the formation of a second C–C bond yielding the formally [2+4] cycloadduct 9 , or a C–O bond yielding the formally [4+2] cycloadduct 10 . The second cycloaddition is a stepwise proce…

A remarkable rearrangement during reaction between triazolopyridinium ylides and dimethyl acetylenedicarboxylate

1991

Abstract The ylides from 2-acylmethyltriazolopyridinium salts ( 1 ) react with dimethyl acetylenedicarboxylate in toluene solution to give the 7-pyrroleninylpyrazolo[1,5-a]pyridines ( 5 ).

Toward an Understanding of the Molecular Mechanism of the Reaction between 1-Methylpyrrole and Dimethyl Acetylenedicarboxylate. An ab Initio Study

1998

The molecular mechanism for the reaction between 1-methylpyrrole and dimethyl acetylenedicarboxylate (DMAD) has been studied using ab initio methods. Two alternative reaction pathways have been considered, both of which correspond to stepwise processes with initial, rate-determining formation of a common zwitterionic intermediate. This intermediate is formed by nucleophilic attack of the pyrrole ring to the carbon−carbon triple bond of DMAD. Closure of this intermediate (pathway A) affords a [4 + 2] cycloadduct, whereas intramolecular proton transfer (pathway B) affords a Michael adduct. The much larger potential energy barrier of the second step in pathway B relative to pathway A is respon…

Acridine orange in a pumpkin-shaped macrocycle: Beyond solvent effects in the UV–visible spectra simulation of dyes

2010

Abstract We present simulation of the UV–visible spectra of acridine orange, a widely used photosensitizer for in vivo studies due to its highly environment-dependent spectroscopic properties. This dye has been investigated both in its protonated and neutral forms, either isolated or embedded in a pumpkin-shaped macromolecular cycle (cucurbit-7-uril), using time-dependent density functional theory techniques. To model this macromolecular cycle, two strategies are taken into account, allowing decoupling of the geometric and electrostatic influences of the host on the guest molecules. Experimental data are well-reproduced when using an embedding electrostatic technique, suggesting that such a…

Solvent Control in Electro-Organic Synthesis

2018

Exploiting the solvent control within electro-organic conversions is a far underestimated parameter in prep-scale electrolysis. The beneficial application in several transformations is outlined and in particular discussed for the dehydrogenative coupling of arenes and heteroarenes. This simple electrolytic strategy in fluorinated solvents allows the modulation of the substrate’s nucleophilicity and the stabilization of the intermediates as well as of the final product from over-oxidation.1 Introduction2 Solvent Effects in Kolbe Electrolysis and Anodic Fluorination3 Unique Solvent Effects of 1,1,1,3,3,3-Hexafluoropropan-2-ol (HFIP)4 Anodic Dehydrogenative Coupling Reactions with Use of HFIP …

Estimation of formamide harmonic and anharmonic modes in the Kohn-Sham limit using the polarization consistent basis sets.

2010

Formamide harmonic and anharmonic frequencies of fundamental vibrations in the gas phase and in several solvents were successfully estimated in the B3LYP Kohn-Sham complete basis set limit (KS CBS). CBS results were obtained by extrapolating a power function (two-parameter formula) to the results calculated with polarization-consistent basis sets. Anharmonic corrections using the second order perturbation treatment (PT2) and hybrid B3LYP functional combined with polarization consistent pc-n (n = 0, 1, 2, 3, 4) and several Pople’s basis sets were analyzed for all fundamental formamide vibrational modes in the gas phase and solution. Solvent effects were modeled within a PCM method. The anhar…

Insights into the anion effect on the self assembly of perylene bisimide diimidazolium salts

2017

Abstract We studied how changing the anion affects the self-assembly of three diimidazolium salts bearing a perylene bisimide spacer. In particular we used [BF 4 − ] and [NTf 2 − ] based salts together with a mixed salt bearing both [I − ] and [BF 4 − ] anions. Thermal as well as concentration and temperature dependent spectroscopic investigations revealed that changing the anion impacts on solid state and solution aggregation, leading to articulate thermotropic behaviors and contrasting solvent effects, respectively. We also studied the electrochemical behavior of the salts to verify if changing the anion alters the redox properties of the salts. Finally, different anions also lead to very…

Morphology controlled nano-structures of an octa(phenoxy)-substituted phthalocyaninato zinc complex: solvent effect on the self-assembly behaviour

2014

The 2,3,9,10,16,17,24,25-octakis(phenoxy)phthalocyaninato zinc, (Zn[Pc(OPh)8]) was fabricated into nano-/micro-structures via solution-phase self-assembly. The self-assembling properties of Zn[Pc(OPh)8] in coordinating and non-coordinating solvents (methanol and n-hexane) have been comparatively studied by electronic absorption, fluorescence, Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The conducting properties were evaluated by current–voltage (I–V) measurements. Due mainly to the presence of different intermolecular Zn–O coordination interactions between the Zn[Pc(OPh)…

Supercritical Carbon Dioxide: A Promoter of Carbon-Halogen Bond Heterolysis

2013

as the leaving groupdeparts from the carbon atom prior to the entrance of thenucleophile. Polar protic solvents with high dielectric con-stants promote polar bond heterolysis by providing effectiveH-bonding and electron-pair donation interactions to theleaving group and the incipient carbocation, respectively.Then, the solvent captures the carbocation intermediate togive the corresponding S