Magnitudes of 18 O isotope shifts in 13 C nuclear magnetic resonance spectra of ketones and alcohols

Abstract

The magnitudes of 18 O-induced isotope shifts in 13 C nmr spectra of ketones and aldehydes are dependent on structure and range from about 0.05 ppm to 0.03 ppm for the carbon attached to 18 O. An increase in negative charge density on the carbonyl oxygen or conjugation to an aromatic ring reduces the size of the upfield shift. The shifts in [ 18 O]alcohols are solvent-dependent, range from 0.03 ppm to 0.01 ppm, and tend to decrease in the order tertiary ≥ secondary ≥ primary ≥ phenols.