13C-1H and13C-13C Spin Coupling Behavior in Aldofuranosyl Rings from Density Functional Theory
13C-1H and13C-13C Spin Coupling Behavior in Aldofuranosyl Rings from Density Functional Theory
复制标题
密度泛函理论中呋喃醛糖环中的 13C-1H 和 13C-13C 自旋耦合行为
DOI：
--
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
A. Serianni
中科院分区：
文献类型：
--
作者：
F. Cloran;I. Carmichael;A. Serianni
使用密度泛函理论 (DFT) 对呋喃醛糖、2-脱氧-{β}-D-赤式-呋喃戊糖 (1) 进行从头算分子轨道计算，以评估 DFT 方法在结构优化和 NMR 自旋-自旋耦合常数测定中的性能，然后再将其应用于更复杂的含碳水化合物系统。将 1 的 10 种几何优化包络形式中的计算分子参数（键长、键角、键扭转）和 NMR 自旋-自旋耦合常数 (J) 与之前报道的 HF/6-31G* 优化几何结构进行比较。在早期工作中，首先使用有限场微扰理论和专门设计用于经济地恢复费米接触对 J 贡献的基组在 HF 水平计算 {sup n}J{sub CH} 值。然后通过二阶 Moeller-Plesset 微扰 (MP2) 计算引入电子相关效应对耦合常数的影响。导出的相关校正（即 MP2-HF 值）通过对相关（尽管必然较小）系统进行更精细的二次构型相互作用 (QCISD) 计算获得的因子进行缩放。在本研究中，J 值的费米接触分量直接通过 DFT 计算，大概恢复了电子关联的重要影响，从而消除了缩放的需要。将 DFT 处理得出的 J{sub CH} 值（一键、二键和三键）与之前使用 HF/MP2 方法获得的缩放耦合进行比较。通过直接比较 HF 和 DFT 优化几何结构中 {sup 13}C-{sup 1}H 耦合的 HF 值来评估结构弛豫对 J 的影响。首次在 1 中计算 (DFT) {sup 1}J{sub CC}、{sup 2}J{sub CC}、{sup 3}J{sub CC} 和 {sup 2+3}J{sub CC} 值作为环构象的函数，通过与 HF 计算直接比较来评估相关校正，并提供这些耦合的新结构解释。 “ 较少的
Ab initio molecular orbital calculations using density functional theory (DFT) have been conducted on the aldopentofuranose, 2-deoxy-{beta}-D-erythro-pentofuranose (1) to evaluate the performance of DFT methodology in structural optimization and NMR spin-spin coupling constant determinations prior to its application in more complex carbohydrate-containing systems. Computed molecular parameters (bond lengths, bond angles, bond torsions) and NMR spin-spin coupling constants (J) in the 10 geometrically optimized envelope forms of 1 are compared to those reported previously from HF/6-31G*-optimized geometries. In earlier work, {sup n}J{sub CH} values were first computed at the HF level using finite-field perturbation theory and a basis set specially designed to economically recover the Fermi-contact contribution to J. Electron correlation effects on the coupling constants were then introduced via second-order Moeller-Plesset perturbation (MP2) calculations. The derived correlation corrections (i.e., the MP2-HF values) were scaled by factors obtained from more elaborate quadratic configuration interaction (QCISD) calculations on related, though necessarily smaller, systems. In the present study, the Fermi-contact components of the J values were computed directly via DFT, presumably recovering the important effects of electron correlation and thus obviating the need for scaling. J{sub CH} values (one-, two-, and three-bond) derived from the DFT treatment are compared to scaled couplings obtained more » previously using HF/MP2 methods. The effect of structural relaxation on J is assessed by direct comparison of HF values for the {sup 13}C-{sup 1}H couplings in both HF- and DFT-optimized geometries. {sup 1}J{sub CC}, {sup 2}J{sub CC}, {sup 3}J{sub CC}, and {sup 2+3}J{sub CC} values are computed (DFT) in 1 as a function of ring conformation for the first time, correlation corrections are evaluated by direct comparison with HF calculations, and new structural interpretations of these couplings are provided. « less