Migda Wojciech, Rys Barbara
Department of Organic Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland.
Magn Reson Chem. 2004 May;42(5):459-66. doi: 10.1002/mrc.1366.
DFT/B3LYP calculations of the ground-state conformation of eight cyclic and acyclic acetals are presented and compared with experimental data. Results of single-point GIAO/DFT calculations at five different levels of theory show that isotropic shieldings need to be empirically scaled to achieve agreement with experimental chemical shifts. Statistical evaluation of data indicates that the most accurate prediction of 13C chemical shifts is achieved at the MPW1PW91/6-311G** level of theory. An empirical equation describing the relationship between delta values and shielding constants is postulated. This equation has been applied to the non-chair ground-state conformation of the six-membered acetonide and to the conformationally flexible benzodioxonine derivative. The agreement observed between the experimental and predicted chemical shifts shows that calculations at the MPW1PW91/6-311G** level of theory are adequate for addressing questions of conformation.
本文给出了八种环状和非环状缩醛基态构象的DFT/B3LYP计算结果，并与实验数据进行了比较。在五个不同理论水平下进行的单点GIAO/DFT计算结果表明，各向同性屏蔽需要进行经验标度才能与实验化学位移达成一致。数据的统计评估表明，在MPW1PW91/6 - 311G理论水平下，对13C化学位移的预测最为准确。假定了一个描述δ值与屏蔽常数之间关系的经验方程。该方程已应用于六元缩酮的非椅式基态构象以及构象灵活的苯并二氧六环衍生物。实验化学位移与预测化学位移之间的一致性表明，在MPW1PW91/6 - 311G理论水平下的计算足以解决构象问题。
