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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >~(17)O NMR Chemical Shifts of Polyoxides in Gas Phase and in Solution
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~(17)O NMR Chemical Shifts of Polyoxides in Gas Phase and in Solution

机译：气相和溶液中〜（17）O NMR的化学位移

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摘要

The ~(17)O NMR chemical shift values of polyoxides HO_nH, CH_3O_nH, and CH_3O_nCH_3 (n = 2, 3, 4) were calculated using four different methods (GIAO-HF, GIAO-MP2, GIAO-CCSD(T), and IGLO-DFT) and various basis sets ranging from double to quadruple ζ quality. The ~(17)O shift values depend on the number of O atoms in the polyoxide chain and on the terminal group (H or alkyl) and are spread over a large range (200-600 ppm relative to H_2O) due to a (diamagnetic) shielding effect caused by electron attraction by the electronegative O atom and a (paramagnetic) deshielding effect caused by anomeric delocalization. Solvent shifts result from both nonspecific and specific solvation. Nonspecific solvation normally leads to a shielding of ~(17)O by up to 20 ppm, whereas specific solvation is strongly deshielding, causing a net effect of 20-36 ppm. An empirical scheme is suggested to predict measured values with an accuracy of better than 5 ppm using GIAO-MP2/qzp gas-phase values with GIAO-CCSD(T) estimates of higher-order correlation corrections as well as specific and nonspecific solvation corrections. Averaging of NMR chemical shifts due to the rotational flexibility of the polyoxides has little influence on the measured ~(17)O NMR chemical shifts.
机译：使用四种不同的方法（GIAO-HF，GIAO-MP2，GIAO-CCSD（T）和OH），计算了多氧化物HO_nH，CH_3O_nH和CH_3O_nCH_3（n = 2、3、4）的〜（17）O NMR化学位移值。 IGLO-DFT）和各种基础集，范围从两倍到四倍ζ质量。 〜（17）O位移值取决于多氧化物链中的O原子数和端基（H或烷基），并且由于（抗磁性）而分布在较大的范围内（相对于H_2O为200-600 ppm） ）由负电性O原子吸引电子引起的屏蔽效应和由异头离域化引起的（顺磁性）屏蔽效应。非特异性和特异性溶剂化都会导致溶剂转移。非特异性溶剂化通常会导致高达20 ppm的〜（17）O屏蔽，而特异性溶剂化会强烈地屏蔽掉，从而导致20-36 ppm的净效应。建议采用经验方案，通过使用GIAO-MP2 / qzp气相值和GIAO-CCSD（T）估算高阶相关校正以及特定和非特定溶剂化校正，来以优于5 ppm的精度预测测量值。由于多氧化物的旋转挠性而导致的NMR化学位移的平均值对所测得的〜（17）O NMR化学位移几乎没有影响。

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