Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

Shielding and Indirect Spin–Spin Coupling Tensors in the Presence of a Heavy Atom: An Experimental and Theoretical Study of Bis(phenylethynyl)mercury

“…Because the corrections due to CSA mechanism for protonated carbons are small and the molecular geometry of I is well established, the vibrational corrections to C–H bond lengths are the main factor determining accuracy of the diffusion parameters and in consequence the shielding anisotropy parameter of C α . This bottleneck is characteristic for dipolar-relaxation-based studies of molecular movements. ,,− Assuming a reasonable C–H distance ( r C–H = 0.112 nm) we have come to the results being in agreement with those obtained in the previous work (Table ) . Eventually, we have found that the shielding anisotropy parameters for C α , C β , and Hg atoms of I have been reproduced reasonably well by our theoretical calculations.…”

Anisotropic Reorientation of 9-Methylpurine and 7-Methylpurine Molecules in Methanol Solution Studied by Combining 13C and 14N Nuclear Spin Relaxation Data and Quantum Chemical Calculations

“…During a detailed interpretation of the dipolar relaxation rates, however, the vibrational averaging of the involved dipolar couplings has to be taken into account, which causes some complications to arise. [7][8][9][10][11][12][13][14][15] Moreover, the number of independent data is sometimes insufficient for unambiguous determination of the rotational diffusion tensor. 16,17 The relaxation data set can be, and sometimes has to be, enlarged by including the relaxation rates due to other than dipolar mechanisms and other then R 1 or η relaxation parameters.…”

Interpretation of the Longitudinal 13C Nuclear Spin Relaxation and Chemical Shift Data for Five Bromoazaheterocycles Supported by Nonrelativistic and Relativistic DFT Calculations

“…These T 1,DD parameters could be established from the measured longitudinal relaxation times, T 1 , and NOE enhancement factors using the well-known relationship , T 1 , DD = ( η max / η ) T 1 In the course of the analysis, for a given carbon, the dipolar interactions with all of the protons in the molecule were taken into account. The necessary interatomic distances were adopted from the optimized molecular geometries, except in the case of the directly bonded C–H atoms, where the distance was assumed to be equal to 1.12 Å to compensate for the effects of vibrations. ,− Unfortunately, the data concerning the 13 C··· 1 H dipolar relaxation alone did not allow separation of the diffusion parameters describing reorientations about the axis perpendicular to the ring plane and about the other two axes, as all of the C–H relaxation vectors lay in the ring planes. To overcome this difficulty, we included in the analysis the longitudinal relaxation rates due to the shielding anisotropy mechanism, T 1,SA , estimated for the protonated carbons as T 1 , SA = [ η max / false( η max − η false) ] T 1 If necessary, the so-obtained values were corrected for dipolar relaxation due to 14 N nuclei of directly bonded nitrogens.…”