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Conformational analysis of fluoroacetoxime and of its O ‐methyl ether by 1 H, 13 C and 15 N NMR and theoretical calculations
Author(s) -
Tormena Cláudio F.,
Rittner Roberto,
Abraham Raymond J.,
Basso Ernani A.,
Fiorin Barbara C.
Publication year - 2004
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.682
Subject(s) - chemistry , conformational isomerism , solvation , density functional theory , solvent effects , crystallography , solvent , nmr spectra database , ether , computational chemistry , chemical shift , proton nmr , stereochemistry , spectral line , molecule , physics , organic chemistry , astronomy
The solvent dependence of the 1 H, 13 C and 15 N NMR spectra of ( E )‐fluoroacetoxime [( E )‐FAO] and of ( E )‐fluoroacetoxime O ‐methyl ether [( E )‐FAOME], was examined and the HF, CF and NF couplings are reported. Density functional theory (DFT) at the B3LYP/6–311++g(2df,2p) level with ZPE (zero point energy) correction was used to obtain the rotamer geometries. In both ( E )‐FAO and ( E )‐FAOME the DFT method gave two energy minima corresponding to the cis (F—C—CN, 0°) and gauche (F—C—CN, 124.1°) rotamers. In contrast, in ( Z )‐FAO the DFT method gave only one energy minimum corrsponding to the trans rotamer. The 4 J HF and 1 J CF couplings in ( E )‐FAO were analyzed by solvation theory assuming the cis and gauche forms to give $E_{cis}-E_{gauche} = 3.3 \, {\rm kcal\, mol}^{-1}$ in the vapor phase, decreasing to 1.54 kcal mol −1 in CCl 4 and −1.19 kcal mol −1 in DMSO (1 kcal=4.184 kJ. In ( E )‐FAOME the observed couplings, when analysed similarly by solvation theory, gave $E_{cis}-E_{gauche} = 2.2 \,{\rm kcal\, mol}^{-1}$ in the vapor phase, 0.91 kcal mol −1 in CCl 4 and −1.18 kcal mol −1 in DMSO. The 3 J NF coupling was independent of the molecular conformation, as it did not change with the solvent polarity. Copyright © 2003 John Wiley & Sons, Ltd.