13C NMR chemical shifts of carbonyl groups in substituted benzaldehydes and acetophenones: substituent chemical shift increments |
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Authors: | Patterson-Elenbaum Stephanie Stanley John T Dillner Debra K Lin Shirley Traficante Daniel |
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Institution: | Department of Chemistry, United States Naval Academy, Annapolis, MD 21402, USA. |
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Abstract: | 13C NMR Substituent chemical shift (SCS) increments have been determined for the carbonyl carbon of a variety of substituted benzaldehydes and acetophenones. The 13C NMR chemical shift of the carbonyl carbon can be predicted for many di- and trisubstituted benzaldehydes and acetophenones through simple additivity of the SCS increments. The magnitude and sign of the SCS increments have been explored using Hartree-Fock 6-31G* calculations to determine the natural atomic charges of the carbonyl carbon. When a substituent capable of intermolecular hydrogen bonding is present, deviations from additivity on the order of 2 ppm are observed in dilution experiments; deviations of up to 6 ppm can result from intramolecular hydrogen bonding. |
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Keywords: | NMR 13C NMR benzaldehydes acetophenones substituent chemical shift increments chemical shift prediction reverse π‐polarization hydrogen bonding |
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