Vibrational spectra and normal coordinate analysis of cf3 compounds: Part XLI. Vibrational spectra, normal coordinate analysis and electron diffraction investigation of hexafluoroazomethane and of cis- and trans-1,1,1,4,4,4-hexafluorobut-2-ene

The structure of hexafluoroazomethane, CF 3 N=NCF 3 , has been reinvestigated by electron diffraction and vibrational spectroscopy and a trans conformation confirmed with r(CF) 1.321(3), r(CN) 1.460(6), r(N=N) 1.235(10)Aand ∡(CNN) 113.4(1.6)°. Similarly, the structures of the but-2-enes trans - and cis -CF 3 CH CHCF 3 have been investigated for comparison, and the following parameters ( trans/cis ) have been determined: r(CF) 1.344(2)/1.343(2), r(CC) 1.481(5)/1.492(5), r(C C) 1.296(20)/1.310(16)Aand ∡(CCC) 125.1(1.6)/126.0(0.5)°. The vibrational spectroscopic data, including those of the butenes-d 2 , verify the observed strengthening of the CF bond in the diazene with respect to that in the butenes. Furthermore, a shortening of the CN/CC and N N/C C bonds upon substitution of CH 3 by CF 3 groups in azomethane and but-2-enes is revealed.