13C nuclear magnetic resonance study of the solution-state dynamics of benzene

Abstract

Nuclear spin relaxation-induced polarization transfer is utilized to investigate the reorientational dynamics of liquid benzene. The second rank reorientational correlation time associated with the overall tumbling of the molecular plane, τ⊥=2.2±0.1 ps, and the motional anisotropy, τ⊥/τ∥=2.4±0.4, were determined at 283 K. From the quantitative measure of relaxation-induced three spin order, the proton shielding anisotropy can be determined, ΔσH[1+(3/5)ηH]=−5.3±1.0 ppm.

Diffusion of benzene through the beta zeolite phase

“…Rotation of the normal vector depends on the moment of inertia component in the plane of the molecule, I \ -= 1.46 Â 10 À45 kg m 2 which is smaller than the inertia component about the symmetry axis, I || = 2.93 Â 10 À45 kg m 2 . These results are qualitatively similar to the rotational anisotropy in liquid benzene reported in experimental studies [48][49][50][51][52][53] and MD simulations [48,[54][55][56][57][58]. We see from Fig.…”

Anisotropic Reorientational Dynamics of Toluene in Neat Liquid. A 13C Nuclear Magnetic Relaxation Study

“…Then, the time dependence of the two-spin-order ν 3 (t) ) 〈2Î z Ŝ z 〉(t) is directly related to the signal height differences of the apparent doublet lines in the coupled spectrum. 12,16,26 In the initial slope approximation, all contributions to ν 3 disappear except those by the DD-CSA cross-correlation…”

Anisotropy of Molecular Reorientation in Pure Liquid Benzene Using Nuclear Relaxation of the Longitudinal 13C−H Two-Spin Order

“…Reorientation of the benzene molecule in the liquid state has been the subject of numerous studies. In addition to this abundant literature, reference can be made to the two most recent works dealing with nuclear spin relaxation techniques. , Only two correlations times are needed for describing this rotational motion: τ ⊥ associated with the tumbling of the symmetry axis perpendicular to the molecular plane, and τ ∥ associated with rotation around that axis. It turns out that most relaxation parameters arising from dipolar interactions or quadrupolar interactions (in the case of deuterated benzene) are related to reorientation of in-plane vectors for which the effective correlation time τ i can be expressed as Clearly, the measurement of a relaxation parameter involving an out-of-plane vector is required so as to reach the reorientation anisotropy defined usually by the parameter χ = τ ⊥ /τ ∥ .…”

“…As a matter of fact, it is essentially the 13 C CSA mechanism which has been used 1,2 in order to detemine the parameter χ. However, there seems to be some inconsistencies in the values of χ found in the literature − and it may be worth attempting further derivation of this parameter possibly through novel experimental procedures capable of yielding accurate values for the dipolar and CSA contributions (which should provide τ i for the former and essentially τ ⊥ for the latter). In this respect, the present paper deals with pulse sequences aiming at the determination of dipolar cross relaxation (i) between carbon-13 and its directly bound proton, (ii) between carbon-13 and remote protons including intra- and intermolecular contributions.…”

“…The discrimination between those two types of protons will be performed by selectivity procedures based on the existence of a J coupling between directly bonded 13 C and 1 H. On the other hand, the CSA mechanism will be evaluated by the so-called interference term which arises from a cross-correlation spectral density involving the C−H dipolar interaction and the 13 C CSA mechanism. Coupry et al obtained this parameter by following the creation of the so-called longitudinal spin order from longitudinal magnetization. Let us recall that the longitudinal spin order, represented by the product operator , can be converted into an observable antiphase doublet of splitting J CH , for example, a carbon antiphase doublet by applying a (π/2) x pulse to 13 C; this yields a state represented by .…”