13C NMR chemical shifts of carbonyl groups in substituted benzaldehydes and acetophenones: substituent chemical shift increments.
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.
Patterson-Elenbaum
Stephanie
S
Department of Chemistry, United States Naval Academy, Annapolis, MD 21402, USA.
Stanley
John T
JT
Dillner
Debra K
DK
Lin
Shirley
S
Traficante
Daniel
D