/sup 18/O-isotope effect in /sup 13/C nuclear magnetic resonance spectroscopy. 2. The effect of structure

Journal Article · Wed Jul 02 04:00:00 EDT 1980 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00534a007· OSTI ID:6776177

Risley, J M; Van Etten, R L

A series of /sup 18/O-labeled organic compounds was synthesized in order to study further two aspects of the /sup 18/O-induced shift of natural abundance /sup 13/C NMR signals as compared to the respective /sup 16/O compounds. First, the direct effect of the hybridization of the carbon atom was studied in ethers. The observed effect was a significant decrease in the /sup 18/O-induced upfield shift when the carbon-atom hybridization was changed from sp/sup 3/ to sp/sup 2/. Second, the significance of the functional group on the /sup 18/O-isotope effect was evaluated. The experimental data reveal that the functional group plays an important role in affecting the magnitude of the /sup 18/O-induced shift. Large shifts are observed upon /sup 18/O-substitution in aldehydes and ketones while alcohols and phenols exhibit smaller shifts. Carboxylic acids show the expected intermediate shifts. In addition, a small but experimentally significant substituent-group effect on the carbonyl group /sup 18/O-isotope shift was observed upon changes in alkyl, aryl, or hydrogen substitution. The isotope-induced shift is discussed from a semitheoretical standpoint on the basis of known experimental results and theoretical predictions. In accord with these expectations, the /sup 18/O shift on the /sup 13/C resonance position is dependent both upon the chemical nature and the number of oxygens covalently bonded to the carbon atom.

• Research Organization: Purdue Univ., West Lafayette, IN
• OSTI ID: 6776177
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:14; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ALDEHYDES
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
DATA
ELECTRONIC STRUCTURE
ETHERS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HYBRIDIZATION
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
KETONES
LABELLED COMPOUNDS
LIGHT NUCLEI
MAGNETIC RESONANCE
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OXYGEN 18
OXYGEN ISOTOPES
RESONANCE
SPECTRA
SPECTRAL SHIFT
STABLE ISOTOPES