NMR study of molecular reorientation under fivefold symmetry - solid permethylferrocene

Abstract

The ring reorientation in permethylferrocene has been studied using high resolution solid state 13 c NMR. The constraints which symmetry places upon the number and types of motional parameters which may be determined from the NMR spectrum are discussed. From comparison of the experimental lineshapes in the slow reorientation temperatures range with theoretical models for random rotations and symmetry related jumps, it is concluded that the reorientation occurs as jumps between symmetry related orientations with jumps of 2-n/5 highly favored over 4rr/5. The activation energy derived for the jump process is 13.5 kjoules/mole.

Structure and Dynamics of Homoleptic Beryllocenes: A Solid‐State 9Be and 13C NMR Study

“…These assignments were based primarily on the values of the CS parameters (i.e., d iso , W and k) of each carbon site. As mentioned above, the axial symmetry (k = 1) of Cp' carbon CS tensors has been shown to arise from time-averaging of the d 11 and d 22 components caused by reorientation of the carbocycles, [43,44,72,73] also in agreement with the observation of a single 13 C NMR resonance for both rings in solution. [37] The signals at d = 112.0 and 110.6 ppm are therefore assigned to the h Figure 6.…”

“…Both the axial symmetry of the aromatic carbon CS tensors (i.e., k = 1.0) and the observation of a single Cp' resonance are attributed to the fast reorientation of the Cp' moieties about their ring centroids. [43,44,72,73] Due to the lower overall molecular symmetry of 3, its 13 C NMR spectra (Figure 5c) are relatively complex compared to those of 1 and 2. By spinning the sample at a frequency of v rot = 15 kHz, the spinning sidebands are removed, leaving Be MAS NMR spectra of a) 1, b) 2, and c) 3 at B 0 = 9.4 T. Simulations of 1 and 2 were performed with SIMPSON and that of 3 with WSOLIDS.…”

Effects of Various Types of Molecular Dynamics on 1D and 2D 2H NMR Studied by Random Walk Simulations

“…For example, a correlation function which is equivalent to Eq. [6] except that the two sine functions are replaced by cosine ones is measurable, too. In what follows, we will refer to these types as sin-sin and cos-cos correlation functions, respectively.…”

“…Afterward, the time signals during the solid-echo sequence and the abovementioned four-pulse sequences are calculated using Eqs. [2] and [6], respectively. The phases appearing in these equations, cf.…”

Scalar operators in solid-state NMR

“…The analytical solution for the strong collision limit was first obtained by Alexander and his coworkers [144] in 1977 by use of representation theory of the symmetry groups. Later, Wemmer et al [145,146] 198 matrix A. Based on this matrix manipulation method, we solve the chemical exchange process in strong collision limit following the convention given by Mehring [19].…”