Theoretical study on electronic structures and spectroscopic regularities of ethylated single-walled carbon nanotubes
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Using atomic electronegativity interaction vector (AEIV) as a parameter to describe the local chemical microenvironment of carbon atoms and the γ parameter, we built a model to calculate 13C NMR chemical shifts in aliphatic ethers. The results obtained from 139 13C NMR chemical shifts in 17 aliphatic ethers showed that the correlation coefficients R of model's estimated value and leave-one-out (LOO) cross-validation (CV) predicted value are 0.995 7 and 0.994 2, respectively. Furthermore, the model was validated using the 13C NMR chemical shifts of 13C atoms in 5 other aliphatic ethers as testing samples, and the correlation coefficients (Qext) obtained was found to be 0.996 3. The results of this study showed that the parameter AEIV correlates well to the 13C NMR chemical shifts of aliphatic ether.
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Electronegativity
Williamson ether synthesis
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Proton NMR
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Chemical shift
Coupling constant
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Nitrated benzo[a]pyrenes are known to be mutagenic, carcinogenic and teratogenic to bacterial and animal cells. For differentiation of isomers and environmental analytical trace studies, spectroscopic information is necessary. The present studies report the 13C NMR spectra of 1-, 3- and 6-nitrobenzo[a]pyrene measured in CDCl3. Complete 13C NMR assignments based on 2D NMR spectroscopy (HMQC and HMBC) were carried out. Further, the computation of fifty 13C chemical shifts of 1-, 3-, and 6-nitrobenzo[a]pyrenes by using GIAO B3LYP/6-311+G(d,p)//B3LYP/6-31+G(d), 6-31+G(d,p), 6-311+G(d), 6-311+G(d,p), 6-311G(d,p) levels of theory was investigated. For 1-, 3- and 6-NBaP the calculated chemical shifts δcalc versus δexpt plots of chemical shifts fall on a linear correlation line with r2 > 0.90. The GIAO B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p)level of theory was found to yield chemical shifts in good agreement with experiment with r2 > 0.90. The most expensive method (larger basis set) has provided the best agreement with the experiment. It is therefore important to continue to seek computational methods that can predict precise chemical shifts in nitrated or related compounds.
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Adamantane
Natural bond orbital
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Geometry optimizations for three isomers of fullerene C84, 21, 22 and 23, have been performed by density functional theory (DFT) at the B3LYP/6-31G* level of theory. 13C NMR chemical shifts were evaluated by the GIAO method employing 6-31G* and 6-311G** basis sets. Isomers 22 and 23 are predicted to have essentially equal energies and isomer 21 to be 16 kcal mol−1 less stable. The calculated 13C NMR chemical shifts of isomers 22 and 23 agree nicely with experimental data while the results of isomer 21 show large differences, indicating that isomer 22 is the experimentally observed D2 isomer.
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Cis–trans isomerism
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Abstract A 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.
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Cyclopropane
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Polarizable continuum model
Quantum chemical
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งานวจยนเปนศกษาทางเคมคำนวณหา chemical shift ของ 1H and 13C NMR ของอนพนธของแมงโกสตนไดแก แอลฟา-แมงโกสตน แกมมา-แมงโกสตน และการซโนน ด ดวยระเบยบวธ WP04, WC04 และ B3LYP และ 6-311+G(2d,p) basis set ทงนพบวาคาทไดจากการคำนวณมความสอดคลองกบคาทมการรายงานจากการทดลอง การเปรยบเทยบความสามารถในการคำนวณ chemical shift ของ 1H and 13C NMR ดวยระเบยบวธทงสามขางตนนนไดรายงานในรปแบบของกราฟแสดงคาผดพลาดสมบรณตอชวงการทำนาย chemical shift ซงพบวาระเบยบวธ WP04, และ B3LYP สามารถใหขอมล chemical shift ของ 1H NMR ทใกลเคยงคาจากการทดลองมากทสดในชวงของ downfield region นอกจากนงานวจยยงไดรายงานการวเคราะหการถดถอยเชงเสน (Linear regression analysis) เพอแสดงความสมพนธระหวาง chemical shift ของ 1H and 13C NMR ทไดจากการคำนวณกบขอมลทไดจากการทดลอง ซงพบวาระเบยบวธ WP04, WC04 และ B3LYP มประสทธภาพในการทำนาย chemical shift ของ 1H and 13C NMR ของอนพนธของแมงโกสตนคอ แอลฟา-แมงโกสตน แกมมา-แมงโกสตน และการซโนน ด ไดเปนอยางด This work reveals the calculation methods in characterizing 1H and 13C NMR chemical shifts of xanthone derivatives, -mangostin, -mangostin and Garcinone D. The calculated chemical shifts were computed at WP04, WC04 and B3LYP density functional levels with the 6-311+G(2d,p) basis set. The calculation values for both 1H and 13C chemical shifts fitted well with experimental values. The performance of the WP04, WC04 and B3LYP functional for 1H and 13C chemical shift prediction is compared to other methods as the plot of absolute errors in the chemical shift prediction. An analysis of errors in 1H chemical shift as a function of the experimental chemical shift values indicates that there are more accurate in the downfield region for both WP04 and B3LYP. The errors show the large significant error in the upfield region for 1H chemical shift. The linear regression comparisons of theoretical and experimental 1H and 13C chemical shift data are also reported in this work. It is found that WP04, WC04 and B3LYP have shown the regression slopes and intercepts most near unity for -mangostin, -mangostin and Garcinone D.
Chemical shift
Proton NMR
Xanthone
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