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1.
Gary E. Martin Kirill A. Blinov R. Thomas Williamson 《Magnetic resonance in chemistry : MRC》2013,51(5):299-307
Unsymmetrical and generalized indirect covariance processing methods provide a means of mathematically combining pairs of 2D NMR spectra that share a common frequency domain to facilitate the extraction of correlation information. Previous reports have focused on the combination of HSQC spectra with 1,1‐, 1,n‐, and inverted 1JCC 1,n‐ADEQUATE spectra to afford carbon–carbon correlation spectra that allow the extraction of direct (1JCC), long‐range (nJCC, where n ≥ 2), and 1JCC‐edited long‐range correlation data, respectively. Covariance processing of HMBC and 1,1‐ADEQUATE spectra has also recently been reported, allowing convenient, high‐sensitivity access to nJCC correlation data equivalent to the much lower sensitivity n,1‐ADEQUATE experiment. Furthermore, HMBC‐1,1‐ADEQUATE correlations are observed in the F1 frequency domain at the intrinsic chemical shift of the 13C resonance in question rather than at the double‐quantum frequency of the pair of correlated carbons, as visualized by the n,1, and m,n‐ADEQUATE experiments, greatly simplifying data interpretation. In an extension of previous work, the covariance processing of HMBC and 1,n‐ADEQUATE spectra is now reported. The resulting HMBC‐1,n‐ADEQUATE spectrum affords long‐range carbon–carbon correlation data equivalent to the very low sensitivity m,n‐ADEQUATE experiment. In addition to the significantly higher sensitivity of the covariance calculated spectrum, correlations in the HMBC‐1,n‐ADEQUATE spectrum are again detected at the intrinsic 13C chemical shifts of the correlated carbons rather than at the double‐quantum frequency of the pair of correlated carbons. HMBC‐1,n‐ADEQUATE spectra can provide correlations ranging from diagonal (0JCC or diagonal correlations) to 4JCC under normal circumstances to as much as 6JCC in rare instances. The experiment affords the potential means of establishing the structures of severely proton‐deficient molecules. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
《Magnetic resonance in chemistry : MRC》2018,56(8):775-781
Recently, it has been reported that large nJCC correlations can sometimes be observed in 1,1‐ADEQUATE spectra with significant intensity, which opens the possibility of structural misassignment. In this work, we have focused on pyrimidine‐based compounds, which exhibit multiple bond correlations in the 1,1‐ADEQUATE experiment as a consequence of 3JCC coupling constants greater than 10 Hz. Results are supported by both the experimental measurement of 3JCC coupling constants in question using J‐modulated‐ADEQUATE and density functional theory calculations. 相似文献
3.
Josep Saurí Yizhou Liu R. Thomas Williamson Gary E. Martin 《Magnetic resonance in chemistry : MRC》2016,54(4):341-345
Despite the tremendous usage of HMBC to establish long‐range 1H–13C and 1H–15N heteronuclear correlations, an inherent drawback of the experiment is the indeterminate nature of the nJXH correlations afforded by the experiment. A priori there is no reliable way of determining whether a given nJCH correlation is, for example, via two‐, three‐, or sometimes even four‐bonds. This limitation of the HMBC experiment spurred the development of the ADEQUATE family of NMR experiments that rely on, in the case of 1,1‐ADEQUATE, an out‐and‐back transfer of magnetization via the 1JCC homonuclear coupling constant, which is significantly larger than nJCC (where n = 2–4) couplings in most cases. Hence, the 1,1‐ADEQUATE experiment has generally been assumed to unequivocally provide the equivalent of 2JCH correlations. The recent development of the 1,1‐ and 1,n‐HD‐ADEQUATE experiments that can provide homodecoupling for certain 1JCC and nJCC correlations has increased the sensitivity of the ADEQUATE experiments significantly and can allow acquisition of these data in a fraction of the time required for the original iterations of this pulse sequence. With these gains in sensitivity, however, there occasionally come unanticipated consequences. We have observed that the collapse of proton multiplets, in addition to providing better s/n for the desired 1JCC correlations can facilitate the observation of typically weaker 2JCC correlations across intervening carbonyl resonances in 1,1‐HD‐ADEQUATE spectra. Several examples are shown, with the results supported by the measurement of the 2JCC coupling constants in question using J‐modulated‐HD‐ADEQUATE and DFT calculations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
4.
Gary E. Martin R. Thomas Williamson Kirill A. Blinov Clemens G. Anklin Wolfgang Bermel 《Magnetic resonance in chemistry : MRC》2012,50(10):691-695
1,1‐ADEQUATE and the related long‐range 1,n‐ and n,1‐ADEQUATE variants were developed to provide an unequivocal means of establishing 2JCH and the equivalent of nJCH correlations where n = 3,4. Whereas the 1,1‐ and 1,n‐ADEQUATE experiments have two simultaneous evolution periods that refocus the chemical shift and afford net single quantum evolution for the carbon spins, the n,1‐variant has a single evolution period that leaves the carbon spin to be observed at the double quantum frequency. The n,1‐ADEQUATE experiment begins with an HMBC‐type nJCH magnetization transfer, which leads to inherently lower sensitivity than the 1,1‐ and 1,n‐ADEQUATE experiments that begin with a 1JCH transfer. These attributes, in tandem, serve to render the n,1‐ADEQUATE experiment less generally applicable and more difficult to interpret than the 1,n‐ADEQUATE experiment, which can in principle afford the same structural information. Unsymmetrical and generalized indirect covariance processing methods can complement and enhance the structural information encoded in combinations of experiments e.g. HSQC‐1,1‐ or ?1,n‐ADEQUATE. Another benefit is that covariance processing methods offer the possibility of mathematically combining a higher sensitivity 2D NMR spectrum with for example 1,1‐ or 1,n‐ADEQUATE to improve access to the information content of lower sensitivity congeners. The covariance spectrum also provides a significant enhancement in the F1 digital resolution. The combination of HMBC and 1,1‐ADEQUATE spectra is shown here using strychnine as a model compound to derive structural information inherent to an n,1‐ADEQUATE spectrum with higher sensitivity and in a more convenient to interpret single quantum presentation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
5.
Gary E. Martin 《Journal of heterocyclic chemistry》2012,49(3):716-720
Posaconazole is a structurally complex triazole antifungal agent that, by virtue of its structural complexity, provides a good test molecule for the evaluation of NMR structure elucidation methodologies. Although GHMBC and related long‐range 1H–13C heteronuclear shift correlation techniques are extremely powerful, at the same time, when dealing with unknowns, they can be problematic in that there is no way to readily differentiate adjacent (2 JCH) correlations from longer range correlations, e.g., 3JCH and nJCH, n > 3. The 1,1‐ADEQUATE experiment, in contrast, provides unequivocal experimental access to adjacent carbon–carbon correlation information, albeit with a sensitivity penalty, as the experiment involves an adjacent 13C–13C out‐and‐back magnetization transfer. In part, the sensitivity penalty can be overcome by using unsymmetrical indirect covariance or general indirect covariance processing methods. The application of these methods through the coprocessing of multiplicity‐edited GHSQC and 1,1‐ADEQUATE data to generate an HSQC‐ADEQUATE correlation plot is demonstrated for posaconazole. 相似文献
6.
Utilizing 13C‐13C connectivity networks for the assembly of carbon skeletons from HSQC‐ADEQUATE spectra was recently reported. HSQC‐ADEQUATE data retain the resonance multiplicity information of the multiplicity‐edited GHSQC spectrum and afford a significant improvement in the signal‐to‐noise (s/n) ratio relative to the 1,1‐ADEQUATE data used in the calculation of the HSQC‐ADEQUATE spectrum by unsymmetrical indirect covariance (UIC) processing methods. The initial investigation into the computation of HSQC‐ADEQUATE correlation plots utilized overnight acquisition of the 1,1‐ADEQUATE data used for the calculation. In this communication, we report the results of an investigation of the reduction in acquisition time for the 1,1‐ADEQUATE data to take advantage of the s/n gain during the UIC processing to afford the final HSQC‐ADEQUATE correlation plot. Data acquisition times for the 1,1‐ADEQUATE spectrum can be reduced to as little as a few hours, while retaining excellent s/n ratios and all responses contained in spectra computed from overnight data acquisitions. Concatenation of multiplicity‐edited GHSQC and 1,1‐ADEQUATE data also allows the interrogation of submilligram samples with 1,1‐ADEQUATE data when using spectrometers equipped with 1.7‐mm Micro CryoProbes ?. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
7.
Gary E. Martin R. Thomas Williamson Peter G. Dormer Wolfgang Bermel 《Magnetic resonance in chemistry : MRC》2012,50(8):563-568
ADEQUATE experiments provide an alternative to the more commonly employed GHMBC experiment for the establishment of long‐range heteronuclear connectivities. The 1,1‐ADEQUATE experiment allows the unequivocal identification of both protonated and non‐protonated carbon resonances adjacent to a protonated carbon. The 1,n‐ADEQUATE experiment establishes correlations via an initial 1JCH heteronuclear transfer followed by an nJCC out‐and‐back transfer, most typically, via three carbon–carbon bonds. Hence, the 1,n‐ADEQUATE experiment allows the equivalent of 4JCH heteronuclear correlations to be probed when they are not observed in a GHMBC spectrum. Aside from the lower sensitivity of the 1,n‐ADEQUATE experiment relative to GHMBC experiments, the interpretation of the former is also complicated by the ‘leakage’ of 1JCC correlations into the spectrum that must be identified. A method for the inversion of 1JCC correlations to facilitate the interpretation of 1,n‐ADEQUATE spectra is presented that allows a single experiment to be performed to access 1JCC and nJCC correlation information. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
John V. Hanna Dr. Kevin J. Pike Dr. Thibault Charpentier Dr. Thomas F. Kemp Dr. Mark E. Smith Prof. Bryan E. G. Lucier Robert W. Schurko Prof. Lindsay S. Cahill Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(10):3222-3239
A variable B0 field static (broadline) NMR study of a large suite of niobate materials has enabled the elucidation of high‐precision measurement of 93Nb NMR interaction parameters such as the isotropic chemical shift (δiso), quadrupole coupling constant and asymmetry parameter (CQ and ηQ), chemical shift span/anisotropy and skew/asymmetry (Ω/Δδ and κ/ηδ) and Euler angles (α, β, γ) describing the relative orientation of the quadrupolar and chemical shift tensorial frames. These measurements have been augmented with ab initio DFT calculations by using WIEN2k and NMR‐CASTEP codes, which corroborate these reported values. Unlike previous assertions made about the inability to detect CSA (chemical shift anisotropy) contributions from NbV in most oxo environments, this study emphasises that a thorough variable B0 approach coupled with the VOCS (variable offset cumulative spectroscopy) technique for the acquisition of undistorted broad (?1/2?+1/2) central transition resonances facilitates the unambiguous observation of both quadrupolar and CSA contributions within these 93Nb broadline data. These measurements reveal that the 93Nb electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the NbV positions, with CQ values in the 0 to >80 MHz range being measured; similarly, the δiso (covering an approximately 250 ppm range) and Ω values (covering a 0 to approximately 800 ppm range) characteristic of these niobate systems are also sensitive to structural disposition. However, their systematic rationalisation in terms of the Nb? O bond angles and distances defining the immediate NbV oxo environment is complicated by longer‐range influences that usually involve other heavy elements comprising the structure. It has also been established in this study that the best computational method(s) of analysis for the 93Nb NMR interaction parameters generated here are the all‐electron WIEN2k and the gauge included projector augmented wave (GIPAW) NMR‐CASTEP DFT approaches, which account for the short‐ and long‐range symmetries, periodicities and interaction‐potential characteristics for all elements (and particularly the heavy elements) in comparison with Gaussian 03 methods, which focus on terminated portions of the total structure. 相似文献
9.
Ryan D. Cohen Josep Saurí Chelsea A. Huff Shane W. Krska Gary E. Martin 《Magnetic resonance in chemistry : MRC》2016,54(11):897-900
1,1‐ADEQUATE is a powerful and robust NMR experiment to establish carbon–carbon connectivities using modest sample quantities when cryogenic probe technology is available. Yet potential pitfalls of applying this method are not widely appreciated, such as weak or missing 1JCC correlations in strongly coupled 13C‐13C AB spin systems and unusually large multi‐bond (nJCC) correlations associated with particular functional groups. These large nJCC correlations observed in 1,1‐ADEQUATE spectra could be mistaken for 1JCC correlations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
10.
Gary E. Martin Kirill A. Blinov Mikhail Reibarkh R. Thomas Williamson 《Magnetic resonance in chemistry : MRC》2012,50(11):722-728
Establishing the carbon skeleton of a molecule greatly facilitates the process of structure elucidation, leaving only heteroatoms to be inserted, heterocyclic rings to be closed, and stereochemical features to be defined. INADEQUATE, and more recently PANACEA, have been the only means of coming close to the goal of totally defining the carbon skeleton of a molecule. Unfortunately, the extremely low sensitivity and prodigious sample requirements of these experiments and the multiple receiver requirement for the latter experiment have severely restricted the usage of these experiments. Proton‐detected ADEQUATE experiments, in contrast, have considerably higher sensitivity and more modest sample requirements. By combining experiments such as 1,1‐ADEQUATE and 1,n‐ADEQUATE with higher sensitivity experiments such as GHSQC through covariance processing, sample requirements can be further reduced with a commensurate improvement in the s/n ratio and F1 resolution of the covariance processed spectrum. We now wish to report the covariance processing of an inverted 1JCC 1,n‐ADEQUATE experiment with a non‐edited GHSQC spectrum to afford a spectrum that can trace the carbon skeleton of a molecule with the exception of correlations between quaternary carbons. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
11.
Mauro V. De Almeida Mara Rubia C. Couri João Vitor De Assis Cleber P. A. Anconi Hélio F. Dos Santos Wagner B. De Almeida 《Magnetic resonance in chemistry : MRC》2012,50(9):608-614
Density functional theory (DFT) calculations of 1H NMR chemical shifts for l ‐quebrachitol isomers were performed using the B3LYP functional employing the 6‐31G(d,p) and 6‐311 + G(2d,p) basis sets. The effect of the solvent on the B3LYP‐calculated NMR spectrum was accounted for using the polarizable continuum model. Comparison is made with experimental 1H NMR spectroscopic data, which shed light on the average uncertainty present in DFT calculations of chemical shifts and showed that the best match between experimental and theoretical B3LYP 1H NMR profiles is a good strategy to assign the molecular structure present in the sample handled in the experimental measurements. Among four plausible O‐methyl‐inositol isomers, the l ‐quebrachitol 2a structure was unambiguously assigned based only on the comparative analysis of experimental and theoretical 1H NMR chemical shift data. The B3LYP infrared (IR) spectrum was also calculated for the four isomers and compared with the experimental data, with analysis of the theoretical IR profiles corroborating assignment of the 2a structure. Therefore, it is confirmed in this study that a combined experimental/DFT spectroscopic investigation is a powerful tool in structural/conformational analysis studies. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
12.
The relatively large chemical shift differences observed in the 1H NMR spectra of the anticholinergic drugs (?)‐scopolamine 1 and (?)‐hyoscyamine 2 measured in CDCl3 are explained using a combination of systematic/molecular mechanics force field (MMFF) conformational searches and gas‐phase density functional theory (DFT) single point calculations, geometry optimizations and chemical shift calculations within the gauge including/invariant atomic orbital (GIAO) approximation. These calculations show that both molecules prefer a compact conformation in which the phenyl ring of the tropic ester is positioned under the tropane bicycle, clearly suggesting that the chemical shift differences are produced by the anisotropic effect of the aromatic ring. As the calculations fairly well predict these experimental differences, diastereotopic NMR signal assignments for the two studied molecules are proposed. In addition, a cursory inspection of the published 1H and 13C NMR spectra of different forms of 1 and 2 in solution reveals that most of them show these diastereotopic chemical shift differences, strongly suggesting a preference for the compact conformation quite independent of the organic or aqueous nature of the solvent. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
13.
Synthesis,Optical Properties,and Electronic Structures of Tetrakis(pentafluorophenyl)tetrathiaisophlorin Dioxide
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Dr. Vijay Lakshmi Mishra Prof. Taniyuki Furuyama Prof. Nagao Kobayashi Prof. Kenta Goto Dr. Takaaki Miyazaki Prof. Jye‐Shane Yang Prof. Teruo Shinmyozu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9190-9197
The synthesis, structure, optical and redox properties, and electronic structure of tetrakis(pentafluorophenyl)tetrathiaisophlorin dioxide ( 12 ) are reported. Oxidation of tetrakis(pentafluorophenyl)tetrathiaisophlorin ( 11 ) with dimethyldioxirane afforded the oxidized product, which was the tetrathiaisophlorin with two thiophene 1‐oxide moieties ( 12 ). More significant nonplanarity and greater bond length alternation in 12 than those of 11 were observed by X‐ray structural analysis. The absorption spectrum of 12 contains two bands at λ=348 and 276 nm, with a weak tail that extends to λ≈650 nm. Analysis of the magnetic circular dichroism spectrum of 12 , based on Michl's 4N‐perimeter model and molecular orbital calculations, indicate that the broad band at λ=348 nm appears to contain N2 and P2 bands, and 12 is classified as a 4nπ system, similar to 11 . The nuclear‐independent chemical shift values and 1H NMR spectroscopy data indicate that 12 has more antiaromatic character than 11 . 相似文献
14.
《Magnetic resonance in chemistry : MRC》2002,40(9):589-594
The 31P chemical shift (CS) tensors of the 1,3,2‐diazaphospholenium cation 1 and the P‐chloro‐1,3,2‐diazaphospholenes 2 and 3 and the 31P and 19F CS tensors of the P‐fluoro‐1,3,2‐diazaphospholene 4 were characterized by solid‐state 31P and 19F NMR studies and quantum chemical model calculations. The computed orientation of the principal axes system of the 31P and 19F CS tensors in the P‐fluoro compound was found to be in good agreement with experimentally derived values obtained from evaluation of P–F dipolar interactions. A comparison of the trends in the chemical shifts of 1 – 4 with further available literature data confirms that the unique high shielding of δ11 in the cation 1 can be related to the effective π‐conjugation in the five‐membered heterocycle, and that a further systematic decrease in δ11 for the P‐halogen derivatives 2 – 4 is attributable to the increased perturbation of the π‐electron distribution by interaction with the halide donor. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
15.
Wei Zhang 《Magnetic resonance in chemistry : MRC》2013,51(7):431-434
A one‐step method was reported for the synthesis of 6‐acetamido‐3‐(N‐(2‐(dimethylamino) ethyl) sulfamoyl) naphthalene‐1‐yl 7‐acetamido‐4‐hydroxynaphthalene‐2‐sulfonate by treating 7‐acetamido‐4‐hydroxy‐2‐naphthalenesulfonyl chloride with equal moles of N, N‐dimethylethylenediamine in acetonitrile in the presence of K2CO3. The chemical structure of the obtained compounds was characterized by MS, FTIR, 1H NMR, 13C NMR, gCOSY, TOCSY, gHSQC, and gHMBC. The chemical shift differences of 1H and 13C being δ 0.04 and 0.2, respectively, were unambiguously differentiated. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
16.
Hashim Farooq Denis Courtier‐Murias Ronald Soong Hussain Masoom Werner Maas Michael Fey Rajeev Kumar Martine Monette Henry Stronks Myrna J. Simpson André J. Simpson 《Magnetic resonance in chemistry : MRC》2013,51(3):129-135
A method is presented that combines Carr–Purcell–Meiboom–Gill (CPMG) during acquisition with either selective or nonselective excitation to produce a considerable intensity enhancement and a simultaneous loss in chemical shift information. A range of parameters can theoretically be optimized very rapidly on the basis of the signal from the entire sample (hard excitation) or spectral subregion (soft excitation) and should prove useful for biological, environmental, and polymer samples that often exhibit highly dispersed and broad spectral profiles. To demonstrate the concept, we focus on the application of our method to T1 determination, specifically for the slowest relaxing components in a sample, which ultimately determines the optimal recycle delay in quantitative NMR. The traditional inversion recovery (IR) pulse program is combined with a CPMG sequence during acquisition. The slowest relaxing components are selected with a shaped pulse, and then, low‐power CPMG echoes are applied during acquisition with intervals shorter than chemical shift evolution (RCPMG) thus producing a single peak with an SNR commensurate with the sum of the signal integrals in the selected region. A traditional 13C IR experiment is compared with the selective 13C IR‐RCPMG sequence and yields the same T1 values for samples of lysozyme and riverine dissolved organic matter within error. For lysozyme, the RCPMG approach is ~70 times faster, and in the case of dissolved organic matter is over 600 times faster. This approach can be adapted for the optimization of a host of parameters where chemical shift information is not necessary, such as cross‐polarization/mixing times and pulse lengths. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
17.
The influence of a two‐step chemical activation on 1,5‐H and 1,6‐H shift reactions of hydroxyl‐peroxy radicals formed in the atmospheric photooxidation of isoprene was investigated by means of a master equation analysis. To account for multiple chemical activation processes, three master equations were coupled. The general approach of this coupling is described, and consequences for steady‐state regimes are examined. The specific calculations show that chemical activation has no substantial influence on the rate coefficients of the above‐mentioned reactions under tropospheric conditions. However, it is demonstrated that high‐pressure limits of the thermal rate coefficients instead of the falloff‐corrected values have to be used for kinetic modeling. This is a consequence of the continuous population of the high‐energy part of the isoprene‐OH‐O2 adduct distribution by the forming reactions under steady‐state conditions. The rate coefficients of the isomerization reactions at T = 298 K were calculated to be k3a∞ = 1.5 × 10?3 s?1 (1,5‐H‐shift of the 1,2‐isomer) and k4a∞ = 6.5 s?1 (1,6‐H‐shift of the (Z)‐1,4‐isomer). The calculated value of k4a∞ is three orders of magnitude larger than a recently reported experimentally observed rate coefficient for the hydrogen shift reactions of the hydroxyl‐peroxy intermediates. It is shown that this discrepancy is in part due to the fact that the experiment does not distinguish between different structural isomers. A comparison of the experimentally determined isotope effect with the calculated value shows a reasonable agreement. 相似文献
18.
《Magnetic resonance in chemistry : MRC》2002,40(3):182-186
15N NMR data of a series of 3‐alkyl[aryl] substituted 5‐trichloromethyl‐1,2‐dimethyl‐1H‐pyrazolium chlorides (where the 3‐substituents are H, Me, Et, n‐Pr, n‐Bu, n‐Pe, n‐Hex, (CH2)5CO2Et, CH2Br, Ph and 4‐Br‐C6H4), are reported. The 15N substituent chemical shifts (SCS) parameters are determined and these data are compared with the 13C SCS values and data obtained by MO calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
19.
Namik Özdemi̇r Bi̇lge Eren Muharrem Di̇nçer Yunus Bekdemi̇r 《International journal of quantum chemistry》2011,111(12):3112-3124
The title molecule, 2‐(4‐chlorophenyl)‐1‐methyl‐1H‐benzo[d]imidazole (C14H11ClN2), was prepared and characterized by 1H NMR, 13C NMR, IR, and single‐crystal X‐ray diffraction. The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the title compound in the ground state have been calculated by using the Hartree‐Fock (HF) and density functional theory (DFT/B3LYP) method with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and GIAO 1H and 13C NMR chemical shifts show good agreement with experimental values. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and nonlinear optical (NLO) properties of the title compound were investigated by theoretical calculations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
20.
Celina Alvarez‐Cisneros Marcelo A. Muñoz Oscar R. Suárez‐Castillo Nury Pérez‐Hernández Carlos M. Cerda‐García‐Rojas Martha S. Morales‐Ríos Pedro Joseph‐Nathan 《Magnetic resonance in chemistry : MRC》2014,52(9):491-499
Long‐range coupling constants 5JHortho,OMe were measured in series of methoxyindoles, methoxycoumarins, and methoxyflavones by the modified J doubling in the frequency domain method. The COSY and NOESY spectra revealed the coupling of the –OMe group with a specific proton at the ortho position and its preferred conformation. Homonuclear 1H–1H couplings were confirmed by irradiation of the –OMe signal. Density functional theory calculations of 5JHortho,OMe using the modified aug‐cc‐pVTZ basis set evidenced that the Fermi contact term shows good agreement with the experimental J values. Accurate chemical shift and coupling constant values followed after iterative quantum mechanical spectral analysis using the PERCH software. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献