Nuclear relaxation, molecular motions and interactions

Abstract

The t4N quadrupolar relaxation time for pyrrole as the pure liquid and in solution in 1,4-dioxan, pyridine, 3,5-1utidine and 2-fluoropyridine has been determined from the line-shape analysis of the imido proton magnetic resonance signal. The dependence of the line shape on solute concentration and temperature was studied and the activation parameters for molecular reorientation determined. INTRODUCTIONNuclear magnetic relaxation measurements can provide valuable information on molecular motions and interactions in liquids. However, the main difficulty in interpreting such information lies in the separation of the observed relaxation time into contributions from different mechanisms (e.g. dipole-dipole, scalar, spin-rotation) which arise from both intra and inter-molecular motions. The problem is considerably simplified [1, 2] if the nuclei under study are relaxed by the quadrupole mechanism, since this can be two or three orders of magnitude more efficient than competing mechanisms, including relaxation by dissolved oxygen. Furthermore, quadrupole relaxation is normally governed by intramolecular motions only, since the contributions of inter-molecular motions to the local electric-field gradients are very small and separation of translational effects is not needed.Many papers have dealt with studies of molecular motions in pure liquids but so far much less attention has been paid to strongly interacting systems such as those involving hydogen-bonded or charge-transfer interactions [3]. Mixtures of hydrogen-bonded liquids offer an interesting possibility for these studies.

Addressing the Exigent Role of a Coumarin Fluorophore toward Finding the Suitable Microenvironment of Biomimicking and Biomolecular Systems: Steering to Project the Drug Designing and Drug Delivery Study

“…The emission maxima of 4-AC in different solvents are red-shifted with increasing polarity of the solvent. The red shift is ∼50 nm, which supports the polar nature of the emissive state, and the variations of the emission maxima of 4-AC in different solvents (Table ) are in accordance with its empirical polarity parameters E T (30) by Reichardt. , …”

“…The emission of 4-AC molecule is governed by the polarity/polarizability π*, hydrogen bond-donating ability α, and hydrogen bond-accepting ability β of different solvents, , and for this, Kamlet–Taft multiparameter approach is used. These parameters for different solvents and the Stokes shift of emission of 4-AC in different solvents are provided in Table .…”

Radical polymerization of diallylamine compounds: From quantum chemical modeling to controllable synthesis of high‐molecular‐weight polymers

“…Using the NMR 1 H spectra of equimolar (1-TFA) mixture and newly synthesized (1 ⅐ TFA) salt in aprotic solvent, we have shown that compound 1 is in protonated form [30]. The base being protonated in the presence of an acid in an aprotic solvent ensures [28] that monomer 1 exists in only the protonated form in the aqueous solutions of (1-TFA) mixture and (1 ⅐ TFA) salt.…”

“…According to published data [28,29], the ion complexes with proton transfer are formed with the largest probability in equimolar systems of amines with trifluoroacetic acid (TFA) (complexes of allyl compounds with different acids were not studied in the literature). These observations predetermined selecting the TFA as a protonizing agent.…”

Stereochemical Equivalence of PIII-Bonded Hydrogen Atoms and |SeIV Lone Electron Pairs in Sr(H2PO3)2 and Sr(HSeO3)2

“…[6,25] ), the high frequency δ(OH) and γ(OH) bands can be assigned to the stronger intra-layer hydrogen bond O13ϪH13···O22, whereas the respective low frequency bands belong to the weaker inter-layer hydrogen bond O23ϪH23···O22. For both compounds, the respective pairs δ(OH)/d(O···O) and γ(OH)/d(O···O) fulfil the corresponding frequency vs.…”