Premium
Conformational effects on 13 C NMR parameters in alkyl formates
Author(s) -
de Kowalewski Dora G.,
Kowalewski Valdemar J.,
Contreras Rubén H.,
Diez Ernesto,
Esteban Angel L.
Publication year - 1998
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199805)36:5<336::aid-omr273>3.0.co;2-c
Subject(s) - conformational isomerism , chemistry , alkyl , intramolecular force , coupling constant , chemical shift , ab initio , spectral line , carbon 13 nmr , computational chemistry , formate , atom (system on chip) , proton nmr , crystallography , stereochemistry , molecule , organic chemistry , physics , particle physics , astronomy , computer science , embedded system , catalysis
The 13 C 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. 13 C chemical shifts and 1 J (CH) couplings are compared for both types of rotamers. Their differences are rationalized in terms of different intramolecular interactions. The 17 O NMR spectra of these compounds could be observed only for the most abundant rotamer, which in all cases was identified as the s ‐ cis rotamer. In the three members of this series with the shortest alkyl chains, a 2 J ( 17 O, 1 H) coupling constant of ca . 40 Hz was observed. In ethyl formate, 13 C magnetic shielding constants were calculated using the LORG approach with ab initio optimized geometries in both types of rotamers for the carbon atom β to the dicoordinated oxygen atom. A comparison between the calculated and experimental values yields support for the rationalizations quoted above. © 1998 John Wiley & Sons, Ltd.