Katritzky Alan R, Akhmedov Novruz G, Doskocz Jacek, Mohapatra Prabhu P, Hall C Dennis, Güven Alâattin
Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA.
Magn Reson Chem. 2007 Jul;45(7):532-43. doi: 10.1002/mrc.1967.
The B3LYP/6-31+G(d) molecular geometry optimized structures of 17 five-membered heterocycles were employed together with the gauge including atomic orbitals (GIAO) density functional theory (DFT) method at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p) and B3LYP/6-311+G(2d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants. The method of geometry optimization for pyrrole (1), N-methylpyrrole (2) and thiophene (7) using the larger 6-311++G(d,p) basis sets at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,p) and B3LYP/cc-pVTZ levels of theory gave little difference between calculated and experimental values of coupling constants. In general, the (1)H and 13C chemical shifts for all compounds are in good agreement with theoretical calculations using the smaller 6-31 basis set. The values of nJHH(n=3, 4, 5) and rmnJ(CH)(n=1, 2, 3, 4) were predicted well using the larger 6-31+G(d,p) and 6-311++G(d,p) basis sets and at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p) levels of theory. The computed atomic charges [Mülliken; Natural Bond Orbital Analysis (NBO); Merz-Kollman (MK); CHELP and CHELPG] for the B3LYP/6-311++G(d,p) geometry optimized structures of 1-17 were used to explore correlations with the experimental proton and carbon chemical shifts.
17个五元杂环的B3LYP/6 - 31 + G(d)分子几何优化结构，与包含原子轨道的规范（GIAO）密度泛函理论（DFT）方法一起，在B3LYP/6 - 31 + G(d,p)、B3LYP/6 - 311++G(d,p)和B3LYP/6 - 311 + G(2d,p)理论水平下，用于计算质子和碳化学位移以及耦合常数。使用较大的6 - 311++G(d,p)基组，在B3LYP/6 - 31 + G(d,p)、B3LYP/6 - 311++G(d,p)、B3LYP/6 - 31 + G(2d,p)和B3LYP/cc - pVTZ理论水平下，对吡咯（1）、N - 甲基吡咯（2）和噻吩（7）进行几何优化的方法，在耦合常数的计算值和实验值之间差异不大。一般来说，所有化合物的（1）H和13C化学位移与使用较小的6 - 31基组进行的理论计算结果吻合良好。使用较大的6 - 31 + G(d,p)和6 - 311++G(d,p)基组，以及在B3LYP/6 - 31 + G(d,p)、B3LYP/6 - 311++G(d,p)、B3LYP/6 - 31 + G(2d,2p)理论水平下，对nJHH（n = 3, 4, 5）和rmnJ(CH)（n = 1, 2, 3, 4）的值进行了良好预测。对1 - 17的B3LYP/6 - 311++G(d,p)几何优化结构计算得到的原子电荷[穆利肯；自然键轨道分析（NBO）；默茨 - 科尔曼（MK）；CHELP和CHELPG]，用于探索与实验质子和碳化学位移的相关性。
