The title compound (1) is prepared in satisfactory yield by reacting CH2N2 with trifluoroacetic anhydride in Et2O; the d-analog was obtained by exchange with D2O. 1H, 13C, 15N, 17O, and 19F NMR spectra of 1 were studied, as well as its IR spectrum. A single isomer is present corresponding to the more stable Z configuration. The structural assignment was made on the basis of quantum mechanical calculations, which revealed that the Z form is some 13.4 kJ mol−1 more stable than the E form and the activation energy for the E → Z transition is 64.2 kJ mol−1. Mass spectra under different experimental conditions were recorded and breakdown pathways of the parent ion of 1 charted. Key words: 3-diazo-1,1,1-trifluoro-2-propanone; 3-d-3-diazo-1,1,1-trifluoro-2-propanone; structure; 1H, 13C, 15N, 17O, and 19F NMR; EI-MS.
