Formation and reactivity of 1-pyrrolyl-2,2,2-trifluoroethyl cations

1990 ◽  
Vol 68 (10) ◽  
pp. 1709-1713 ◽  
Author(s):  
Annette D. Allen ◽  
Jean-Marc Kwong-Chip ◽  
Wing Cheung Lin ◽  
Paul Nguyen ◽  
Thomas T. Tidwell
Keyword(s):  
Rate Ratio ◽  
Electrophilic Substitution ◽  
Pyrrole Ring ◽  
Solvent Polarity ◽  
Nucleophilic Attack ◽  
Charge Delocalization ◽  
Polarity Parameter ◽  
High Degree ◽  
Low K

1-(1-Methyl-2-pyrrolyl)-2,2,2-trifluoroethyl p-nitrobenzoate (3) reacts by carbocation formation with an m value for the dependence of rate on the solvent polarity parameter YOTs of 0.56, and a rate 41 times slower than (1-methyl-2-pyrrolyl)methyl p-nitrobenzoate. The products from 3 include significant amounts of material derived from solvent attack at the 5-position of the pyrrole ring. The results indicate a high degree of charge delocalization by the strongly donating pyrrolyl group, resulting in a low k(H)/k(CF3) rate ratio and nucleophilic attack on the ring. 1,1, l-Trifluoro-2-(1-methyl-2-pyrrolyl)propan-2-ol (10) reacted with CF3CO2H via a tertiary carbocation, which led to dimeric products resulting from electrophilic substitution on the pyrrole ring. Keywords: pyrrole, trifluoromethyl substituents, carbocations.

Determination of the empirical solvent polarity parameter ET(30) by multivariate image analysis

2013 ◽  
Vol 5 (4) ◽  
pp. 891-896 ◽  
Author(s):  
Fatemeh Shakerizadeh-Shirazi ◽  
Bahram Hemmateenejad ◽  
Abdol Mohammad Mehranpour
Keyword(s):  
Image Analysis ◽  
Solvent Polarity ◽  
Multivariate Image Analysis ◽  
Polarity Parameter ◽  
Multivariate Image

scholarly journals Crystal Structure of a 9-Subunit Archaeal Exosome in Pre-Catalytic States of the Phosphorolytic Reaction

Archaea ◽  
2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Esben Lorentzen ◽  
Elena Conti
Keyword(s):  
Accurate Determination ◽  
Nucleophilic Attack ◽  
Divalent Metal Ions ◽  
Mechanism Of Catalysis ◽  
Rna Exosome ◽  
Eukaryotic Organisms ◽  
High Degree ◽  
Shed Light ◽  
Positively Charged

The RNA exosome is an important protein complex that functions in the 3′ processing and degradation of RNA in archaeal and eukaryotic organisms. The archaeal exosome is functionally similar to bacterial polynucleotide phosphorylase (PNPase) and RNase PH enzymes as it uses inorganic phosphate (Pi) to processively cleave RNA substrates releasing nucleoside diphosphates. To shed light on the mechanism of catalysis, we have determined the crystal structures of mutant archaeal exosome in complex with either Pi or with both RNA and Pi at resolutions of 1.8 Å and 2.5 Å, respectively. These structures represent views of precatalytic states of the enzyme and allow the accurate determination of the substrate binding geometries. In the structure with both Pi and RNA bound, the Pi closely approaches the phosphate of the 3′-end nucleotide of the RNA and is in a perfect position to perform a nucleophilic attack. The presence of negative charge resulting from the close contacts between the phosphates appears to be neutralized by conserved positively charged residues in the active site of the archaeal exosome. The high degree of structural conservation between the archaeal exosome and the PNPase including the requirement for divalent metal ions for catalysis is discussed.

scholarly journals A fluorescent paramagnetic Mn metal–organic framework based on semi-rigid pyrene tetracarboxylic acid: sensing of solvent polarity and explosive nitroaromatics

IUCrJ ◽  
2015 ◽  
Vol 2 (5) ◽  
pp. 552-562 ◽  
Author(s):  
Alankriti Bajpai ◽  
Arindam Mukhopadhyay ◽  
Manchugondanahalli Shivakumar Krishna ◽  
Savitha Govardhan ◽  
Jarugu Narasimha Moorthy
Keyword(s):  
Metal Ions ◽  
Metal Organic Framework ◽  
Energy Charge ◽  
Fluorescence Emission ◽  
Solvent Polarity ◽  
Accessible Volume ◽  
Polarity Parameter ◽  
Metal Organic ◽  
Paramagnetic Metal ◽  
Organic Framework

An Mn metal–organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-LMOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt's solvent polarity parameter (ETN). Further, the applicability of Mn-Lto the sensing of nitroaromaticsviafluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.

Non Linear Optical, Thermodynamic Analysis and Spectroscopic Investigation of GPA Optical Materials

2017 ◽  
Vol 730 ◽  
pp. 106-111
Author(s):  
Xiao Jing Liu ◽  
Xin Sun ◽  
Jing Hua Guo
Keyword(s):  
Optical Materials ◽  
Density Functional ◽  
Nonlinear Optical ◽  
Energy Gap ◽  
Chemical Reactivity ◽  
Nbo Analysis ◽  
Basis Sets ◽  
Nucleophilic Attack ◽  
Charge Delocalization ◽  
Different Temperatures

In this work, density functional theory (DFT) calculations with B3LYP/6-311++G(d,p) basis sets was used to explore the electronic, structural, nonlinear optical and thermal properties aspects of glycine-phthalic acid (GPA) optical materials. Dipole moment, static polarizability and first hyperpolarizability analysis of the molecule have been performed. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. MEP study confirms GPA as an electron rich species and explains its electrophilic nature. MEP shows that this molecule has several possible sites for electrophilic/nucleophilic attack in which V(r) calculations provide insights into the order of preference. The low value of HOMO-LUMO energy gap reflects the high chemical reactivity, low chemical stability and hardness of GPA molecule. Thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (Cp), standard entropies (S) and standard enthalpy (H) increase with rise in temperature. These results discussed in this study will upsurge the knowledge to design and synthesize new type nonlinear optical materials with exceptional chemical and physical properties.

The art of discovery in biophysical organic chemistry

2005 ◽  
Vol 83 (9) ◽  
pp. 1207-1211 ◽  
Author(s):  
Edward M Kosower
Keyword(s):  
Organic Chemistry ◽  
Solvent Effect ◽  
Charge Transfer Complex ◽  
Solvent Polarity ◽  
Physical Organic Chemistry ◽  
Stable Free Radical ◽  
Physical Organic ◽  
Polarity Parameter ◽  
Insight Into ◽  
Made In

Observations made in the course of experiments on pyridinium salts led to important discoveries in physical organic chemistry. The way in which the discoveries were made is likened to art rather than goal-directed "cold logic". We can describe the art of discovery as an effort enhanced by practice and intuition to recognize novelty in a finding and provide productive insight into its nature. We shall present some examples, and describe what happened after finding an unexpected light absorption band, a surprising solvent effect on spectra, and an unexpectedly stable and beautiful small organic radical.Key words: art of discovery, solvent polarity parameter, charge-transfer complex, stable free radical, solvent effect on spectra.

Solvent effect on the dipole moments and photo physical behaviour of 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene dye

2013 ◽  
Vol 91 (12) ◽  
pp. 1107-1113 ◽  
Author(s):  
J.S. Kadadevarmath ◽  
G.H. Malimath ◽  
N.R. Patil ◽  
H.S. Geethanjali ◽  
R.M. Melavanki
Keyword(s):  
Excited State ◽  
Room Temperature ◽  
Dipole Moments ◽  
Emission Spectra ◽  
Solvent Polarity ◽  
Solvatochromic Shift ◽  
Shift Method ◽  
Tert Butyl ◽  
Solvatochromic Shift Method ◽  
Polarity Parameter

The absorption and emission spectra of fluorescent thiophene dye, namely, 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene, have been recorded at room temperature in solvents of different polarities. The excited state dipole moments (μe) were estimated from Lippert’s, Bakhshiev’s, and Kawski–Chamma–Viallet’s equations using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The optimized geometry of the molecule and μg were calculated theoretically by Gaussian 03 software using B3LYP/6-31g* level of theory. The μg and μe were calculated by means of solvatochromic shift method and μe was determined in combination with μg. It was observed that μe were higher than those of the μg, indicating a substantial redistribution of the π-electron densities in a more polar excited state for the selected thiophene dye. Further, the change in the dipole moment (Δμ) was calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter [Formula: see text] and values are compared.

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