Structure of the products of condensation of hydroxylamine with trifluoromethyl‐β‐diketones: assignments of the diastereotopic protons of the 4‐methylene group in 5‐hydroxy‐5‐trifluoromethyl‐Δ 2 ‐isoxazolines

The combined use of 1 H NMR spectroscopy with theoretical calculations of chemical shifts (GIAO) and coupling constants (B3LYP/6‐311 ++G**) of a 5‐hydroxy‐5‐trifluoromethyl‐Δ 2 ‐isoxazoline has enabled solving the problem of the assignments of the diastereotopic protons in this compound. This result has been extended to 5‐hydroxy‐5‐trifluoromethyl‐Δ 2 ‐pyrazolines and the corresponding 5‐trichloromethyl derivatives. Copyright © 2005 John Wiley & Sons, Ltd.