NMR vs. molecular modelling. Part II—steroid chemical shift calculations
✍ Scribed by William B. Smith
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 62 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Using the steroid hormone estrone as a model, DFT GIAO calculations of 13C chemical shifts were performed using geometries determined by di †erent methods and di †erent basis sets for the GIAO calculations. It was found that considerable savings in CPU time could be e †ected by using geometries determined by molecular mechanics using the MMX force Ðeld. The best results for the GIAO chemical shift calculation were obtained with the BPW91/6È311G** basis set. However, replacement by the more rapid BPW91/3È21G* basis set gave reasonable results only if one used an augmented basis set for those atoms which were part of the aromatic or carbonyl structures or attached to the oxygen heteroatoms. Using the MMX force Ðeld, satisfactory results were obtained for cholesterol using the BPW91/6È31G** basis set, serving as a compromise to the previously mentioned basis sets.