Conformational effects on 13C NMR parameters in alkyl formates

✍ Scribed by Dora G. de Kowalewski; Valdemar J. Kowalewski; Rubén H. Contreras; Ernesto Diez; Angel L. Esteban

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 219 KB
• Volume: 36
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199805)36:5<336::aid-omr273>3.0.co;2-c

✦ Synopsis

The 13C NMR spectra of a series of alkyl formates which show the coexistence of s-cis and s-trans rotamers at room temperature were measured at 125 MHz. 13C chemical shifts and 1J(CH) couplings are compared for both types of rotamers. Their di †erences are rationalized in terms of di †erent intramolecular interactions. The 17O NMR spectra of these compounds could be observed only for the most abundant rotamer, which in all cases was identiÐed as the s-cis rotamer. In the three members of this series with the shortest alkyl chains, a 2J(17O,1H) coupling constant of ca. 40 Hz was observed. In ethyl formate, 13C magnetic shielding constants were calculated using the LORG approach with ab initio optimized geometries in both types of rotamers for the carbon atom b to the dicoordinated oxygen atom. A comparison between the calculated and experimental values yields support for the rationalizations quoted above.