Analysis of the NMR and Double-Resonance Spectra of the Isomers of N2F2

Abstract

The assignment of F19 NMR spectra of the two isomers of N2F2 is consistent with the assumption of trans and cis 1,2-difluorodiazine structures for these molecules. The qualitative features of the F19—{N14} double-resonance spectra, and a comparison of the F19 NMR spectra at 56.4 and 40.0 Mc/sec strongly favor a cis structure over a 1,1-difluorodiazine structure for the more reactive isomer. A comparison of the indirect N–F coupling constants for the two isomers indicates that the FNN angles are probably quite different for cis and trans N2F2.

N.M.R. spectra of molecules containing quadrupolar nuclei

“…The only references known to us are the paper [5], in which the zAaXaY system is treated theoretically in order to show the basic conceptual weakness of the analogy with chemical exchange, the papers [8,10,12] in which several systems are discussed theoretically from the viewpoint of scalar relaxation of the second kind, and the paper [14] which has been discussed in w 2.4 above. It is the purpose of this section to discuss an experimental spectrum of this type, namely the 19F spectrum of the cis isomer of N2F 2, which has been previously recorded ( figure 3) by other workers [27], in order to illustrate the extra information which bandshape analysis can yield. The original treatment [27] did not use the bandshape, but only the line positions and intensities.…”

“…It is the purpose of this section to discuss an experimental spectrum of this type, namely the 19F spectrum of the cis isomer of N2F 2, which has been previously recorded ( figure 3) by other workers [27], in order to illustrate the extra information which bandshape analysis can yield. The original treatment [27] did not use the bandshape, but only the line positions and intensities. Moreover the authors [27] made the potentially self-contradictory assumption that the rate of quadrupolar relaxation of the 14N nuclei was sufficiently rapid for JNN' to be effectively zero, but was sufficiently slow for a standard spectral analysis of the system in terms of the remaining coupling constants to be valid.…”

“…The original treatment [27] did not use the bandshape, but only the line positions and intensities. Moreover the authors [27] made the potentially self-contradictory assumption that the rate of quadrupolar relaxation of the 14N nuclei was sufficiently rapid for JNN' to be effectively zero, but was sufficiently slow for a standard spectral analysis of the system in terms of the remaining coupling constants to be valid. It will be shown below that the magnitude of the neglected (N, N) coupling constant may be as large as 33 Hz and that it does not appear possible to obtain a satisfactory fit to the spectral bandshape (using earlier [27] values of J~F, JNF', and JFF') assuming this coupling constant to vanish.…”

“…Moreover the authors [27] made the potentially self-contradictory assumption that the rate of quadrupolar relaxation of the 14N nuclei was sufficiently rapid for JNN' to be effectively zero, but was sufficiently slow for a standard spectral analysis of the system in terms of the remaining coupling constants to be valid. It will be shown below that the magnitude of the neglected (N, N) coupling constant may be as large as 33 Hz and that it does not appear possible to obtain a satisfactory fit to the spectral bandshape (using earlier [27] values of J~F, JNF', and JFF') assuming this coupling constant to vanish. The computations were carried out in the standard way using QUADREDOCOS except that all transitions of intensity less that 10 -6 were omitted from the equations (1) ; this automatically eliminates all transitions between symmetric and anti-symmetric eigenkets, which cannot affect the bandshape [10] (see the discussion in w 2.3).…”

A 14N nuclear magnetic resonance study on nitrogen–oxygen–halogen compounds

“…has found only limited use in spite of the high natural abundance of the 14N isotope (99.635 %). Whereas a fairly large number of spectra of organic compounds (1) have been recorded, only a very few studies are concerned with inorganic compounds (1,(2)(3)(4)(5). For many inorganic nitrogen compounds, handling and corrosion problems exist.…”