scholarly journals Aromaticities of Five Membered Heterocycles through Dimethyldihydropyrenes Probe by Magnetic and Geometric Criteria

2015 ◽  
Vol 2015 ◽  
pp. 1-11
Author(s):  
Maria ◽  
Khurshid Ayub
Keyword(s):  
Chemical Shifts ◽  
Reference Models ◽  
H Nmr ◽  
Quantitative Estimates ◽  
Shift Analysis ◽  
Structural Criterion ◽  
Stabilization Energies ◽  
Suitable Reference ◽  
Chemical Shift Analysis ◽  
Aromatic Stabilization

Aromaticities of five membered heterocycles, containing up to three heteroatoms, are quantified through the dimethyldihydropyrene (DHP) probe. Bond fixation caused by the fusion of heterocycles to the dimethyldihydropyrene nucleus (DHPN) was measured by changes in the1H NMR chemical shifts (magnetic) and bond lengths alterations (structural criterion). Chemical shifts of dihydropyrenes were calculated at GIAO HF/6-31G(d)//B3LYP/6-31+G(d). For1H NMR chemical shift analysis, two nonaromatic reference models are studied. Among the studied heterocycles, pyrazole and triazole are about 80–85% aromatic relative to benzene, through both magnetic and geometric criteria. Thiazole and oxazoles are found least aromatic where quantitative estimates of aromaticities are about 34–42%, relative to benzene. These quantitative estimates of aromaticities of five membered heterocycles are also comparable to those from aromatic stabilization energies. The quantification of aromaticity through energetic, magnetic, and structural criteria can deliver the similar inferences provided that suitable reference systems are chosen.

Using NMR chemical shifts to calculate the propensity for structural order and disorder in proteins

2012 ◽  
Vol 40 (5) ◽  
pp. 1014-1020 ◽  
Author(s):  
Kamil Tamiola ◽  
Frans A.A. Mulder
Keyword(s):  
Structural Information ◽  
Chemical Shifts ◽  
Disordered Proteins ◽  
Photoactive Yellow Protein ◽  
Structural Protein ◽  
Online Tool ◽  
Order And Disorder ◽  
Aggregation Behaviour ◽  
Shift Analysis ◽  
Chemical Shift Analysis

NMR spectroscopy offers the unique possibility to relate the structural propensities of disordered proteins and loop segments of folded peptides to biological function and aggregation behaviour. Backbone chemical shifts are ideally suited for this task, provided that appropriate reference data are available and idiosyncratic sensitivity of backbone chemical shifts to structural information is treated in a sensible manner. In the present paper, we describe methods to detect structural protein changes from chemical shifts, and present an online tool [ncSPC (neighbour-corrected Structural Propensity Calculator)], which unites aspects of several current approaches. Examples of structural propensity calculations are given for two well-characterized systems, namely the binding of α-synuclein to micelles and light activation of photoactive yellow protein. These examples spotlight the great power of NMR chemical shift analysis for the quantitative assessment of protein disorder at the atomic level, and further our understanding of biologically important problems.

QSPR CALCULATION OF AROMATICITY IN SOME FIVE-MEMBERED HETEROAROMATIC COMPOUNDS

2004 ◽  
Vol 03 (02) ◽  
pp. 145-153 ◽  
Author(s):  
PABLO R. DUCHOWICZ ◽  
EDUARDO A. CASTRO
Keyword(s):  
Experimental Data ◽  
Magnetic Susceptibility ◽  
Molecular Descriptors ◽  
Chemical Shifts ◽  
Regression Equations ◽  
Linear Quadratic ◽  
Multilinear Regression ◽  
Heteroaromatic Compounds ◽  
Stabilization Energies ◽  
Aromatic Stabilization

Aromatic stabilization energies (ASE) for a set of 29 five-membered heteroaromatic compounds are calculated using molecular descriptors such as magnetic susceptibility exaltation (Λ), nucleus-independent chemical shifts (NICS), and electrotopological indices (EI) via linear, quadratic and cubic fitting polynomials. Theoretical estimations compare fairly well with experimental data when three variables multilinear regression equations are employed.

Chemical-shift analysis of O Kα by EPMA color-mapping method for BiSrCaCuO superconductive specimen

1992 ◽  
Vol 50 (1) ◽  
pp. 82-83
Author(s):  
H. Takahashi ◽  
T. Okumura ◽  
Y. Seo ◽  
A. Kabaya ◽  
C. Nielsen
Keyword(s):  
Chemical Shift ◽  
Crystal Structures ◽  
Chemical Shifts ◽  
Mapping Method ◽  
Color Mapping ◽  
Shift Analysis ◽  
Spectral Peaks ◽  
Sintering Method ◽  
Chemical Shift Analysis ◽  
Acid Phthalate

The chemical shifts of x-ray spectra are now frequently observed with EPMA (Electron Probe Microanalysis). The conventional method of chemical-shift analysis with EPMA is to compare the peak shapes and peak positions of standard spectra with those of unknown spectra. We reported that O-Kα peak shapes detected by using a TAP (Thallium acid phthalate) crystal reflect their crystal structures. Fig. 1 shows these O-Kα spectral peaks. In the present study, concerning the BiSrCaCuO superconductor made by the sintering method, it was observed that the O-Kα spectra of several kinds of phases reflected their crystal structures. Moreover, it is now possible to observe these chemical shifts of spectra by using the color mapping method in EPMA.

scholarly journals Understanding 125Te NMR chemical shifts in disymmetric organo-telluride compounds from natural chemical shift analysis

2020 ◽  
Vol 22 (4) ◽  
pp. 2319-2326 ◽  
Author(s):  
Ewa Pietrasiak ◽  
Christopher P. Gordon ◽  
Christophe Copéret ◽  
Antonio Togni
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Magnetic Coupling ◽  
Nmr Chemical Shifts ◽  
Shift Analysis ◽  
Theoretical Investigations ◽  
Chemical Shift Analysis

Magnetic coupling of the lone pair: theoretical investigations reveal the origin of 125Te chemical shift in disymmetric organotellurides

scholarly journals 13C and 1H NMR Spectra of Synthetic (25R)-5α-Spirostanes

1999 ◽  
Vol 23 (1) ◽  
pp. 48-49
Author(s):  
Martín A. Iglesias Arteaga ◽  
Carlos S. Pérez Martinez ◽  
Roxana Pérez Gil ◽  
Francisco Coll Manchado
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
1H Nmr Spectra ◽  
H Nmr ◽  
C 23 ◽  
Main Effects ◽  
Nmr Signals

The assignment of 13C and 1H NMR signals of synthetic (25 R)-5α-spirostanes is presented; the main effects on chemical shifts due to substitution at C-23 are briefly discussed.

Chemical shifts of charge-transfer complexes and Buckingham equation

1990 ◽  
Vol 55 (9) ◽  
pp. 2131-2137
Author(s):  
Mahboob Mohammad ◽  
Ather Yaseen Khan ◽  
Tariq Mahmood ◽  
Ismat Fatima ◽  
Riffat Shaheen ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Nmr Spectra ◽  
Charge Transfer Complex ◽  
Chemical Shifts ◽  
Charge Transfer Complexes ◽  
Aprotic Solvents ◽  
Reaction Field ◽  
H Nmr ◽  
Spherical Cavities ◽  
Dipolar Aprotic Solvents

The 1H NMR spectra of the charge-transfer complex of 1-ethyl-4-methoxycarbonylpyridinium iodide have been recorded in various dipolar aprotic solvents. An attempt is made to interpret the chemical shifts in terms of Buckingham's reaction field equation for spherical cavities. A linear dependence has been found between the δ(2,6) values and the square of dielectric function for a spherical cavity, which confirms the validity of the Buckingham equation for this class of compounds.

CC/B–N substitution in five membered heterocycles. A computational analysis

2017 ◽  
Vol 41 (9) ◽  
pp. 3619-3633 ◽  
Author(s):  
Vaibhav A. Dixit ◽  
William R. F. Goundry ◽  
Simone Tomasi
Keyword(s):  
Computational Analysis ◽  
Stabilization Energy ◽  
Stabilization Energies ◽  
Neutral Conditions ◽  
Aromatic Stabilization

Novel five-membered azaboroles are aromatic, stable under neutral conditions, isomer stabilization energy is explained using σ-bond and aromatic stabilization energies.

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