Matsuzaki Keigo, Hayashi Satoko, Nakanishi Waro
Faculty of Systems Engineering, Wakayama University 930 Sakaedani Wakayama 640-8510 Japan
RSC Adv. 2024 Apr 30;14(20):14340-14356. doi: 10.1039/d4ra00843j. eCollection 2024 Apr 25.
O NMR chemical shifts ((O)) were analysed based on the molecular orbital (MO) theory, using the diamagnetic, paramagnetic and total absolute magnetic shielding tensors ((O), (O) and (O), respectively). O was selected as the standard for the analysis. An excellent relationship was observed between (O) and the charges on O for O, O, O, O and O. The data from HO, HO, HO and HO were on the correlation line. However, such relationship was not observed for the oxygen species, other than above. The pre-α, α and β effects were evaluated bases on (O), where the pre-α effect arises from the protonation to a lone pair orbital on O, for an example. The 30-40 ppm and 20-40 ppm (downfield shifts) were predicted for the pre-α and β effects, respectively, whereas the values for the α effect was very small in magnitude, where the effect from the hydrogen bond formation should be considered. Similarly, the carbonyl effect in HC[double bond, length as m-dash]O and the carboxyl effects in H(HO)C[double bond, length as m-dash]O were evaluated from MeOH, together with HC[double bond, length as m-dash]CHOH from CHCHOH. Very large downfield shifts of 752, 425 and 207 ppm were predicted for HC[double bond, length as m-dash]O*, H(HO)C[double bond, length as m-dash]O* and H(HO*)C[double bond, length as m-dash]O, respectively, together with the 81 ppm downfield shift for HC[double bond, length as m-dash]CHO*H. The origin of the effect were visualized based on the occupied-to-unoccupied orbital transitions. As a result, the origin of the O NMR chemical shifts ((O)) can be more easily imaged and understand through the image of the effects. The results would help to understand the role of O in the specific position of a compound in question and the mechanisms to arise the shift values also for the experimental scientists. The aim of this study is to establish the plain rules founded in theory for (O), containing the origin, which has been achieved through the treatments.
基于分子轨道（MO）理论，利用抗磁、顺磁和总绝对磁屏蔽张量（分别为(σ)、(σ)和(σ)）对¹⁷O核磁共振化学位移(δ(¹⁷O))进行了分析。选择¹⁷O作为分析的标准。对于O、O、O、O和O，观察到δ(¹⁷O)与O上的电荷之间存在良好的关系。来自H₂O、H₂¹⁷O、H¹⁷O₂和¹⁷O₂的数据位于相关线上。然而，对于上述以外的氧物种，未观察到这种关系。基于δ(¹⁷O)评估了前α、α和β效应，例如，前α效应源于质子化到O上的孤对轨道。预测前α和β效应的化学位移分别为30 - 40 ppm和20 - 40 ppm（向低场位移），而α效应的值在大小上非常小，其中应考虑氢键形成的影响。同样，从甲醇中评估了H₂C=O中的羰基效应以及H₂(¹⁷O)C=O中的羧基效应，以及从CH₃CH₂¹⁷OH中评估了H₂C=¹⁷CHOH中的羰基效应。预测H₂C=¹⁷O*、H₂(¹⁷O)C=O和H₂(¹⁷O)C=O的向低场位移分别为752、425和207 ppm，以及H₂C=¹⁷CHO*H的向低场位移为81 ppm。基于占据轨道到未占据轨道的跃迁直观显示了该效应的起源。结果，通过效应的图像可以更容易地成像和理解¹⁷O核磁共振化学位移(δ(¹⁷O))的起源。这些结果将有助于理解¹⁷O在相关化合物特定位置中的作用以及产生位移值的机制，这对于实验科学家来说也是如此。本研究的目的是建立基于理论的关于δ(¹⁷O)的简单规则，包括其起源，这已通过这些处理得以实现。
