Importance of cross-correlated relaxation in the spectra of simple organofluorine compounds: Spectral complexity of A(3)B(3)X spin systems compared to ABX spin systems

作者：Alemany Lawrence B^*; Malloy Thomas B Jr; Nunes Megan M; Zaibaq Nicholas G

来源：Journal of Molecular Structure, 2012, 1023: 176-188.

DOI：10.1016/j.molstruc.2012.05.011

• Organfluorine compounds
• Cross-correlated relaxation
• Higher order effects
• Isotope effects
• NMR spin systems
• NMR spectral simulations

In a continuation of our initial investigation of the complex C-13 and F-19 spectra exhibited by two simple organofluorine compounds, additional organofluorine compounds expected to exhibit a wide range of spectral complexity were studied. Spectral simulations are critical for analyzing the more complex spin systems, in particular, A(3)B(3)X and A(6)B(3)X. Cross-correlated relaxation is commonly observed: examples of C-13-F-19 cross-correlated relaxation are shown with the signals for each nucleus exhibiting unequal relaxation rates. Higher order effects are particularly noticeable in the spectra of perfluoro-t-butyl alcohol because of a large (4)J(FF) value in the ((CF3)-C-13)(12CF3)(2)(COH)-C-12 isotopomer. The many additional transitions in an A(3)B(3)X spin system compared to an ABX spin system result in much more complex F-19 (A(3) and B-3) and C-13 (X) spectra, even though only three types of nuclei are involved in each spin system. The corresponding protio compounds typically constitute a much simpler A(3)M(3)X spin system because the long-range (n)J(HH) coupling (n %26gt;= 4) is much smaller than the corresponding long-range (n)J(FF) coupling. Spectra previously published for ethane-1-C-13 (A(3)B(3)X) and hexafluoroethane-1-C-13 (A(3)M(3)X) are notable exceptions and are discussed.

• 出版日期2012-9-12