Über die Temperaturabhängigkeit der 13 C‐NMR.‐Spektren von [5–6‐η‐(1 Z , 5 E )‐Cyclooctadien]tetracarbonyleisen und (1 Z , 5 E )‐Cyclooctadien

On the Temperature Dependence of the 13 C‐NMR. Spectra of [5‐6‐η‐(1Z,5E)‐Cyclooctadien] and of (lZ, 5E)‐Cyclooctadiene The activation parameters of the conformational ring inversion process (simultaneous rotation around the C(3), C(4) and C(7), C(8) bonds; cf . Scheme 1) of the title compounds ( 1 and 2 , respectively) have been determined between 275 L and 155 K by a complete line shape analysis of the temperature dependent proton noise‐modulated decoupled 13 C‐NMR. spectra of 1 and 2 . The temperature dependence of the rates (k( 1 ) and k( 2 ), respectively) of the inversion process can be described by the following equations (no influence of the solvents was observed; E a in J/mol):\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} k(1) = 10^{13,02 \pm 0.35} \,\exp (- (42010 \pm 1470)/{\rm RT)s}^{{\rm - 1}} \\ k(2) = 10^{13,05 \pm 0.17} \,\exp (- (33930 \pm \,\,\,590)/{\rm RT)s}^{{\rm - 1}} \\ \end{array} $$\end{document} . Further data are given in Tables 1 and 2 . The carbonyl groups of the complex 1 show at 180 K , where the ring inversion process is frozen out, a single line at 211 ppm, i. e. the coalescence temperature of the carbonyl groups must be < 180 K .