O-NITROSOBIS(TRIFLUOROMETHYL)HYDROXYLAMINE - UNEXPECTED CONFORMATIONAL PROPERTIES AND AN UNUSUALLY LONG (CF3)2NO-NO BOND - A COMBINED STUDYOF THE GASEOUS AND SOLID STATES

The conformational properties and the geometric structure of gaseous O -nitrosobis(trifluoromethyl)-hydroxylamine, (CF3)2N-O-N=O, have been s tudied by infrared spectroscopy, electron diffraction, and ab initio c alculations. From the relative intensities and band contours of the tw o N=O vibrations, a mixture of 80(10)% trans-syn and 20(10)% trans-ant i conformers (DELTAG = G(syn) - G(anti) = -0.8(3) kcal/mol) is derived (trans describes the orientation of the O-N bond relative to the CNC bisector and syn/anti refers to the orientation of N=O relative to N-O ). Such a mixture of conformers with planar NONO groups is consistent with the electron diffraction intensities. In addition, the compound h as been subjected to X-ray crystal structure analysis. In the solid st ate, only the trans-syn conformer is present. The O-N single bond is u nusually long and differs strongly in the two phases: 1.572(21) angstr om in the gaseous state and 1.669 (3) angstrom in the solid state. The results of ab initio calculations depend strongly on the calculationa l method, especially for the relative energy of the two conformers and for the O-N bond length: DELTAE = E(syn)-E(anti) = -1.8, +0.6, and -3 .3 kcal/mol and O-N = 1.527, 1.401, and 1.717 angstrom with HF/3-21G, HF/6-31G, and MP2/6-31G*, respectively. None of these predictions agr ees very well with the experimental results for the gas phase.