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DOI: 10.1039/A608271H (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1997, 1851-1860

13C NMR calculations on azepines and diazepines

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Rainer Koch, Bernd Wiedel and Curt Wentrup

Abstract

Ab initio and DFT calculations of 13C NMR chemical shifts of 1H-, 2H- and 3H-azepines as well as recently synthesised 1H- and 5H-1,3-diazepines are reported. The reliabilities of the computational methods used for this purpose are evaluated by examining a large number of combinations of basis sets and geometry optimisations. Generally, the Becke3LYP/6-31+G* and HF/6-31G* or HF/6-31+G* single-point calculations based on MP2/6-31G* geometries give the best agreement with experiment (3–4 ppm deviation), better than the corresponding BLYP calculations. Localised orbital methods such as IGLO or LORG do not improve the accuracy. The 1H NMR chemical shifts are also calculated, but the smaller chemical shift range for protons makes the calculated data inherently less precise. Again, Becke3LYP/6-31G* or BLYP/6-31G* with MP2/6-31G* geometries and the HF/6-311+G(3df,2p)//HF/6-31G* combination give the best results. Overall, the 13C NMR calculations in particular are sufficiently precise to be a valuable tool in the identification of novel compounds of this type.

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