Analysis of seven-membered lactones by computational NMR methods: proton NMR chemical shift data are more discriminating than carbon.
Analysis of seven-membered lactones by computational NMR methods: proton NMR chemical shift data are more discriminating than carbon.
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DOI：
10.1021/jo402627s
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发表时间：
2014-01-17
期刊：
影响因子：
--
通讯作者：
Hoye TR
中科院分区：
文献类型：
--
作者：
Marell DJ;Emond SJ;Kulshrestha A;Hoye TR
我们报道了一项构象挑战性的七元内酯的核磁共振化学位移研究（1-11）；计算数据集和实验数据集进行了比较。计算包括对每个内酯进行完整的构象分析，对所有构象的化学位移进行玻尔兹曼加权平均，并对计算的化学位移进行线性校正。DFT几何优化[M06-2X/6-31+G(d,p)]和GIAO核磁共振化学位移计算[B3LYP/6-311+G(2d,p)]提供计算的化学位移。校正后的平均绝对误差（CMAE），即11种内酯中每一种的计算和实验化学位移之间差异的平均值，是令人鼓舞的小（1H时0.02-0.08 ppm， 13C时0.8-2.2 ppm）。使用三对顺式和反式非对映体内酯来评估该方法区分立体异构体的能力。实验位移与两种可能的异构体的计算位移进行了比较。我们引入了“匹配比”的使用-较大（较差的拟合）与较小（较好的拟合）CMAE的比率。匹配比值越大，表示识别能力越强。质子数据[2.4 ~ 4.0 (ave = 3.2)]的匹配比大于碳数据[1.1 ~ 2.3 (ave = 1.6)]，表明前者为区分这些非对映体提供了更好的依据。
We report an NMR chemical shift study of conformationally challenging seven-membered lactones (1–11); computed and experimental data sets are compared. The computations involved full conformational analysis of each lactone, Boltzmann-weighted averaging of the chemical shifts across all conformers, and linear correction of the computed chemical shifts. DFT geometry optimizations [M06-2X/6-31+G(d,p)] and GIAO NMR chemical shift calculations [B3LYP/6-311+G(2d,p)] provide the computed chemical shifts. The corrected-mean absolute error (CMAE), the average of the differences between the computed and experimental chemical shifts for each of the eleven lactones, is encouragingly small (0.02–0.08 ppm for 1H or 0.8–2.2 ppm for 13C). Three pairs of cis vs. trans diastereomeric lactones were used to assess the ability of the method to distinguish between stereoisomers. The experimental shifts were compared with the computed shifts for each of the two possible isomers. We introduce the use of a “match ratio”—the ratio of the larger (worse fit) to the smaller (better fit) CMAE. A greater match ratio value indicates better distinguishing ability. The match ratios are larger for proton data [2.4–4.0 (ave = 3.2)] than for carbon [1.1–2.3 (ave = 1.6)], indicating that the former provide a better basis for discriminating these diastereomers.
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影响因子：
3.2
作者：
Cernuchova, Petra;Mihovilovic, Marko D.
通讯作者：
Mihovilovic, Marko D.
影响因子：
1.7
作者：
DITCHFIELD, R
通讯作者：
DITCHFIELD, R
影响因子：
--
作者：
MCWEENY, R
通讯作者：
MCWEENY, R
影响因子：
4.4
作者：
BECKE, AD
通讯作者：
BECKE, AD
影响因子：
--
作者：
BONDI, A
通讯作者：
BONDI, A