13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXVI. Stereochemical Study of the Septanose Ring

¹³C-¹³C Spin-spin coupling constants of aldoseptanoses of the Dseries were calculated in terms of the self-consistent finite perturbation theory. General relations holding in the stereochemical behavior of the ¹³C-¹³C coupling constants in the septanose ring were determined, which made it possible to perform conformational analysis and assign configuration of the anomeric centers in carbohydrates and products of their metabolism.     

13C-13C Coupling Constants in Structural Studies: XXXIII. Stereochemical Study of the Pyranose Ring

¹³C-¹³C coupling constants for all aldopyranoses of the D-series were calculated in terms of the self-consistent finite perturbation theory. General relations holding in the stereochemical behavior of the ¹³C-¹³C coupling constants for the pyranose ring were found. The results obtained make it possible to perform conformational analysis and assign configuration of the anomeric center in molecules of carbohydrates and products of their metabolism, containing a pyranose fragment.     

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXVII. Rotational Conformations of Hydroxy Groups in Pyranose, Furanose, and Septanose Rings

Rotational surfaces for ¹³C-¹³C coupling constants with respect to two dihedral angles at C¹ and C² in model structures of aldopyranoses, aldofuranoses, and aldoseptanoses of the D-series were calculated in terms of the self-consistent finite perturbation theory. Internal rotation of the hydroxy groups exerts an appreciable effect (within 2.5 Hz) on the ¹³C-¹³C coupling constants of all cyclic forms of monosaccharides, which provides the possibility for performing conformational analysis of carbohydrates and their metabolites containing pyranose, furanose, and septanose fragments.     

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXIV. Nonempirical Calculations: Small Heterocycles

An ab initio calculation was carried out for ^{1 3}C-^{1 3}C spin-spin coupling constants in a series of saturated three- and four-membered heterocycles within a framework of second order perturbation theory using an approximation of second order polarization propagator. The accounting for electron correlation effects and the use of correlation-consistent basis sets with addition of functions allowing for internal correlation and of dense functions on nuclei permitted to obtain good quantitative agreement with experimental data.     

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXI. Bicyclo[2.1.0]pentane Heteroanalogs

¹³C-¹³C spin-spin coupling constants and orbital hybridization of the bridging bond in bicyclo[2.1.0]pentane heteroanalogs and their unsaturated derivatives were calculated in terms of the self-consistent finite perturbation theory (SCPT INDO). The results showed that the bridging CÄC bond in all the examined compounds has an anomaloulsy low s character.     

13C-13C Coupling Constants in Structural Studies: XXXII. Additivity of Spin-Spin Couplings in Sterically Strained Heterocycles

Calculations in terms of the self-consistent finite perturbation theory (SCPT) and analysis of contributions of localized molecular orbitals in terms of the polarization propagator theory (CLOPPA) indicate additivity of ¹³C-¹³C coupling constants in saturated sterically strained heterocycles. Their fused derivatives, especially those containing 3rd Period elements, show considerable deviations of the calculated coupling constants from the additive values.     

直接键连原子间的NMR偶合常数的自然杂化轨道研究——Ⅰ.~(13)C—H核自旋偶合常数~1J_(~(13)C-H)

利用CNDO/2分子轨道方法和自然杂化轨道方法,计算了一系列碳氢化合物和含杂原子的碳氢化合物的自然杂化轨道。在此基础上,得到了计算~(13)C—H偶合常数~1J13_(C-H)的简单关系式。对75种不同化学环境下的~1J13_(C-H)的计算结果表明,无论是碳氢化合物系列,还是含杂原子的碳氢化合物系列,计算值与已知实验值都较为吻合。本文还对计算结果作了较详细的讨论。     

Determination of Spin-Spin Coupling Constants J(PP) on the Basis of 13C and 31p NMR Data

Abstract

The diphosphine dioxides Ph₂P (O) CH₂P (O)Ph₂.(I, Ph₂P(O)CH₂CH₂P(O)Ph₂ (II), Ph₂P(O)CH=CHP(O)Ph₂-cis (III), -trans (IV), [Ph₂P(O)] C=CH (V), [Ph₂P(O) 1₂C=PPh₃ (VI), and also non-symmetric Ph₂(P)OCH=CHP(O)PhEt-trans (VII), Et²P(O)CH=CHP(O)PhEt-trans (VIII), have been studied in CH²C1₂ and CHCl₃ solutions by means of ¹³C and ³¹P NMR.     

直接键连原子间的NMR偶合常数的自然杂化轨道研究——Ⅱ.C—C核自旋偶合常数~1J_(~(13)C—~(13)C)

在前文工作的基础上,本文利用CNDO/2分子轨道方法和自然杂化轨道方法,给出了计算一些化合物中碳—碳单键和碳—碳多重键的核自旋偶合常数~1J13的线性关系式。对32种不同碳—碳键偶合常数的计算结果表明,计算值与已知实验值相吻合。本文还对计算结果及影响偶合常数的因素作了相应的讨论。     

13C-13C spin-spin coupling constants in structural studies: XLIII. Stereochemical study on functionalized 3-iminopyrrolizines

Three 1-ethylsulfanyl-3-imino-3H-pyrrolizine-2-carboxamides were synthesized by intramolecular cyclization of substituted (2Z)-2-cyano-3-ethylsulfanyl-3-(1H-pyrrol-2-yl)prop-2-enamides. The products were assigned syn configuration at the C=N bond and preferential s-cis orientation of the carbamoyl group on the basis of the experimental ¹³C-¹³C coupling constants and high-level nonempirical quantum-chemical calculations.     

应用相敏HMQC和HSQC谱准确测定异核碳-氢偶合常数

准确测定各种同核和异核偶合常数是核磁共振（NMR）方法研究的一个非常跃的领域。首先,各种三键偶合常数通过Karplus关系式^[1]反映了相应二面角的大小,因此,多键偶合常数的准确测定直接影响分子结构确定的精确性。其次,由于稀液晶溶剂体系NMR方法的发展^[2],准确测定各种异核键偶合常数也显得非常重要,特别是应用场相关偶合常数研究分子在磁场中的取向时,对异核－键偶合常数测定的准确性要求更加严格^[3]。异核－键偶合常数的最准确的测定方法是异核偶合调制的HSQC（Heteronuclear Single-Quantum Coherence)实验^[3],它通过测定一系列异核耦合调制的二维HSQC谱,对交叉峰的强度进行分析来精确确定相应的异核－键偶合常数。这一方法的缺点是比较费时。作者在异核多键偶合常数的准确测定方面也做了一些有意义的工作^[4-6 α]。在前文^[5]工作的基础上,本文提出了二维相敏HMQC（Heteronuclear Multiple-Quantum Coherence)和HSQC（Heteronuclear Single-Quantum Coherence)实验,用于准确测定异核－键偶合常数。     

Determination of Long Range Proton Carbon Coupling Constants by Modified Semi-Selective Two-Dimensional Inept: An Application in Stereochemical Analysis of Saccharides

Abstract

Long-range proton-carbon coupling constants are useful in the assignment of ¹³C NMR spectra and in stereochemical analysis. The measurement of vicinal coupling constants, ³J_C-H, and their interpretation based on appropriate Karplus-type relationships (e.g. for ³J_H-C-C-C or ³J_H-C-O-C)^1–3 provide valuable information in conformational studies of carbohydrates. Nevertheless, the use of ³J_C-H in carbohydrate studies is rather rare because their measurement is time consuming and analysis of ¹H-coupled ¹³C NMR spectra is complicated. However, 2D NMR methods ^4–6 that allow precise measurement of long-range couplings in a reasonable time have become available recently.     

Spin-spin Coupling Constants <Superscript>13</Superscript>C-<Superscript>13</Superscript>C in Structural Studies: XXXVIII. Nonempirical Calculations: Oximes

Ab initio calculation of spin-spin coupling constants ¹³C-¹³C for a series of ketone oximes was carried out in a framework of the second order polarization propagator approximation (SOPPA). Taking into account the electron correlation effects and the use of special correlation-consistent basic sets including functions allowing for internal correlation and dense functions provided a good agreement between the calculated and experimental values. These results open new possibilities for the configurational assignment of imine nitrogen compounds.     

Computer-Assisted 3D Structure Elucidation (CASE-3D): The Structural Value of 2JCH in Addition to 3JCH Coupling Constants

We present a method to use long-range CH coupling constants to derive the correct diastereoisomer from the molecular constitution of small molecules. A set of 79 ²J_CH and ³J_CH values collected from a single HSQMBC experiment on a sample of strychnine were used in the CASE-3D (computer-assisted 3D structure elucidation) protocol. In addition to the most commonly used ³J_CH coupling constants, the subset of 32 ²J_CH values alone showed an excellent degree of configuration selection. The study is mainly based on comparison of DFT-calculated ^2,3J_CH values with experimental ones, critical for the case of ²J_CH. But the configuration selection also works well using ³J_CH values predicted from a semi-empirical Karplus-based equation limited to H−C−C−C fragments. The robustness, shown using strychnine as a proof of concept, makes the J-based CASE-3D analysis a viable option for the application in fields such as peptide and carbohydrate research, organic synthesis, natural-product identification and analysis, as well as medicinal chemistry.