Accurate calculation of31P NMR chemical shifts in polyoxometalates

2015 ◽  
Vol 17 (14) ◽  
pp. 8723-8731 ◽  
Author(s):  
Magda Pascual-Borràs ◽  
Xavier López ◽  
Josep M. Poblet
Keyword(s):  
Chemical Shifts ◽  
Basis Set ◽  
Accurate Calculation ◽  
Nmr Chemical Shifts

We search for an optimal DFT/basis set combination for computationally reproducing31P NMR chemical shifts in polyoxometalates.

scholarly journals Predicting Heats of Explosion of Nitroaromatic Compounds through NBO Charges and 15N NMR Chemical Shifts of Nitro Groups

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Ricardo Infante-Castillo ◽  
Samuel P. Hernández-Rivera
Keyword(s):  
Cross Validation ◽  
Chemical Shifts ◽  
Quantitative Model ◽  
Nitroaromatic Compounds ◽  
Basis Set ◽  
15N Nmr ◽  
Prediction Ability ◽  
Heat Of Explosion ◽  
Nmr Chemical Shifts ◽  
Nbo Charges

This work presents a new quantitative model to predict the heat of explosion of nitroaromatic compounds using the natural bond orbital (NBO) charge and 15N NMR chemical shifts of the nitro groups (15NNitro) as structural parameters. The values of the heat of explosion predicted for 21 nitroaromatic compounds using the model described here were compared with experimental data. The prediction ability of the model was assessed by the leave-one-out cross-validation method. The cross-validation results show that the model is significant and stable and that the predicted accuracy is within 0.146 MJ kg−1, with an overall root mean squared error of prediction (RMSEP) below 0.183 MJ kg−1. Strong correlations were observed between the heat of explosion and the charges (R2 = 0.9533) and 15N NMR chemical shifts (R2 = 0.9531) of the studied compounds. In addition, the dependence of the heat of explosion on the presence of activating or deactivating groups of nitroaromatic explosives was analyzed. All calculations, including optimizations, NBO charges, and 15NNitro NMR chemical shifts analyses, were performed using density functional theory (DFT) and a 6-311+G(2d,p) basis set. Based on these results, this practical quantitative model can be used as a tool in the design and development of highly energetic materials (HEM) based on nitroaromatic compounds.

A New Basis Set for the Calculation of 13C NMR Chemical Shifts within a Non-empirical Correlated Framework

2020 ◽  
Vol 124 (36) ◽  
pp. 7322-7330
Author(s):  
Yuriy Yu. Rusakov ◽  
Irina L. Rusakova ◽  
Valentin A. Semenov ◽  
Leonid B. Krivdin
Keyword(s):  
13C Nmr ◽  
Chemical Shifts ◽  
Basis Set ◽  
Nmr Chemical Shifts ◽  
13C Nmr Chemical Shifts

scholarly journals A theoretical study on 2-chloro-5-(2-hydroxyethyl)-4-methoxy-6-methylpyrimidine by DFT/ab initio calculations

2015 ◽  
Vol 33 (2) ◽  
pp. 369-380
Author(s):  
Hacer Pir Gümüs ◽  
Davut Avci ◽  
Yusuf Atalay ◽  
Ömer Tamer
Keyword(s):  
Energy Level ◽  
Chemical Shifts ◽  
Molecular Geometry ◽  
Energy Difference ◽  
Basis Set ◽  
Nmr Chemical Shifts ◽  
Title Molecule ◽  
Experimental Values ◽  
C Nmr ◽  
Molecular Energy Level

AbstractQuantum chemical calculations have been performed to study the molecular geometry, 1H and 13C NMR chemical shifts, conformational, natural bond orbital (NBO) and nonlinear optical (NLO) properties of the 2-chloro-5-(2-hydroxyethyl)-4- methoxy-6-methylpyrimidine molecule in the ground state using DFT and HF methods with 6-311++G(d,p) basis set. The optimized geometric parameters and 1H and 13C NMR chemical shifts have been compared with the experimental values of the title molecule. The results of the calculations show excellent agreement between the experimental and calculated frequencies at B3LYP/6-311++G(d,p) level. In order to provide a full understanding of the properties of the title molecule in the context of molecular orbital picture, the highest occupied molecular energy level (EHOMO), the lowest unoccupied molecular energy level (ELUMO), the energy difference (DE) between EHOMO and ELUMO, electronegativity (χ), hardness (η) and softness (S) have been calculated using B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) levels. The calculated HOMO and LUMO energies show that the charge transfer occurs within the title molecule.

scholarly journals Quantum-chemical study of C— H bond dissociation enthalpies of various small non-aromatic organic molecules

2013 ◽  
Vol 6 (1) ◽  
pp. 64-72 ◽  
Author(s):  
Peter Poliak ◽  
Adam Vagánek
Keyword(s):  
13C Nmr ◽  
Linear Correlation ◽  
Density Functional ◽  
Chemical Shifts ◽  
Basis Set ◽  
Basis Sets ◽  
Nmr Chemical Shifts ◽  
Bond Dissociation ◽  
13C Nmr Chemical Shifts ◽  
Experimental Values

Abstract In this work, C-H bond dissociation enthalpies (BDE) and vertical ionization potentials (IP) for various hydrocarbons and ketones were calculated using four density functional approaches. Calculated BDEs and IPs were correlated with experimental data. The linearity of the corresponding dependences can be considered very good. Comparing two used functionals, B3LYP C-H BDE values are closer to experimental results than PBE0 values for both used basis sets. The 6-31G* basis set employed with both functionals, gives the C-H BDEs closer to the experimental values than the 6-311++G** basis set. Using the obtained linear dependences BDEexp = f (BDEcalc), the experimental values of C-H BDEs for some structurally related compounds can be estimated solely from calculations. As a descriptor of the C-H BDE, the IPs and 13C NMR chemical shifts have been investigated using data obtained from the B3LYP/6-31G* calculations. There is a slight indication of linear correlation between IPs and C-H BDEs in the sets of simple alkanes and alkenes/ cycloalkenes. However, for cycloalkanes and aliphatic carbonyl compounds, no linear correlation was found. In the case of the 13C NMR chemical shifts, the correlation with C-H BDEs can be found for the sets of alkanes and cycloalkanes, but for the other studied molecules, no trends were detected.

scholarly journals Evaluation of 13C NMR spectra of cyclopropenyl and cyclopropyl acetylenes by theoretical calculations

2004 ◽  
Vol 2 (1) ◽  
pp. 196-213 ◽  
Author(s):  
Valentine Ananikov
Keyword(s):  
13C Nmr ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Cyclopropane Ring ◽  
Density Functional Method ◽  
Basis Set ◽  
Nmr Chemical Shifts ◽  
13C Nmr Chemical Shifts ◽  
Giao Calculations

AbstractA convenient methodology was developed for a very accurate calculation of 13C NMR chemical shifts of the title compounds. GIAO calculations with density functional methods (B3LYP, B3PW91, PBE1PBE) and 6-311+G(2d,p) basis set predict experimental chemical shifts of 3-ethynylcyclopropene (1), 1-ethynylcyclopropane (2) and 1,1-diethynylcyclopropane (3) with high accuracy of 1–2 ppm. The present article describes in detail the effect of geometry choice, density functional method, basis set and effect of solvent on the accuracy of GIAO calculations of 13C NMR chemical shifts. In addition, the particular dependencies of 13C chemical shifts on the geometry of cyclopropane ring were investigated.

Experimental (FT-IR, Laser-Raman and NMR) and theoretical spectroscopic analysis of 3-[(N-methylanilino)methyl]-5-(thiophen-2-yl)-1,3,4-oxadiazole-2(3H)-thione

2017 ◽  
Vol 16 (03) ◽  
pp. 1750024 ◽  
Author(s):  
Yusuf Sert ◽  
Nuri Öztürk ◽  
Fatmah A. M. Al-Omary ◽  
Can Alaşalvar ◽  
Mona M. Al-Shehri ◽  
...  
Keyword(s):  
Molecular Orbital ◽  
Chemical Shifts ◽  
Molecular Structures ◽  
Basis Set ◽  
Spectroscopic Techniques ◽  
Nmr Chemical Shifts ◽  
Laser Raman ◽  
Ft Ir ◽  
Experimental Values ◽  
Vibrational Wavenumbers

The structure of a potential bioactive agent namely, 3-[([Formula: see text]-methylanilino)methyl]-5-(thiophen-2-yl)-1,3,4-oxadiazole-2(3[Formula: see text]-thione was characterized by proton and carbon-13 nuclear magnetic resonance (NMR) chemical shifts, Fourier transform infrared (FT-IR) and Laser-Raman spectroscopic techniques. The quantum chemical computations of molecular structures (disorder I and disorder II forms), vibrational wavenumbers, carbon-13 and proton chemical shifts and UV-Vis spectroscopic parameters have been performed with DFT/B3LYP method at 6-311[Formula: see text]G(d,p) basis set. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), nonlinear optical (NLO) properties and natural bond orbital (NBO) analyses have been theoretically examined with the mentioned calculation level. The calculated values have been compared with the recorded experimental data. The computed molecular geometric parameters, vibrational wavenumbers, NMR chemical shifts, and UV-Vis wavelengths have been found to be in a good harmony with the experimental values and spectral results of similar structures in the literature. We believe that the work will be of considerable interest to anyone working in the area of theoretical chemistry, whether in industry or academics.

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