Nuclear Magnetic Relaxation Measurements on Liquid Acetonitrile and Acetonitrile Water Mixtures

Abstract

Precise temperature dependent H, D,By a new method, the acetonitrile deuterium quadrupole coupling constant was determined to 162(6) kHz.An isotope effect of about 5% on the acetonitrile correlation time of the reorientation of the symmetry axis is observed. It decreases if the water content is increased. For the effective correlation time of the C-H/D vector the isotope effect is about 25%. This effect was separated into a contribution of 3% for only one molecule which is deuterated and 21% for the deuteration of the remaining molecules.The anisotropy of the reorientation of acetonitrile was calculated in the limit of rotational diffusion. In neat deuterated ammonia the reorientation about the symmetry axis is about ten times faster than the reorientation of the symmetry axis itself. Due to different activation energies the anisotropy increases with decreasing temperature. The isotope effect is also anisotropic and the rotational anisotropy in protonated acetonitrile is about fourteen. The anisotropy is higher in the binary mixtures. At the critical composition it is fourteen for the deuterated and twenty for the protonated sample.In the mixture of critical composition simultaneous relaxation measurements on both phases were possible. This allows a determination of the coexistence curve. No anomaly of the rates was observed on approaching the coexistence curve.

How approximate is the experimental evaluation of quadrupole coupling constants in liquids? A novel computational study

“…This is in agreement with the fact that in such systems the overall decrease of quadrupole couplings in the liquid compared to the gas phase is very small. This has been shown in experimental studies of liquid benzene 24 and acetonitrile 25 by one of us ͑E.H.H.͒. The other models in Table I were simulated to study the process in more detail.…”

Dipole–Dipole Coupling Constant for a Directly Bonded CH Pair—A Carbon-13 Relaxation Study

“…Ottiger and Bax (34) determined effective C α H α bond length in a protein, using a dilute liquid crystalline phase as a solvent. Kowalewski and co-workers (35), Gryff-Keller and Molchanov (36), and Hardy and co-workers (37,38) discussed systems where more than one carbon-13 relaxation mechanism needed to be considered and where one of the goals was to determine the interaction strength for the second mechanism. Case reported an analysis of vibrational corrections based on ab initio calculations (39).…”

Dielectric response and collective dynamics of acetonitrile

“…5, line 1) as their value at 298.15 K, τ or = 3.68 ps, significantly exceeds corresponding data of Refs. [8][9][10]17,46] and of the present work (τ D = 3.32 ps; τ′/g K = 2.89 ps). Additionally, their slope of τ or vs. η/T is markedly different.…”

“…Similarly, the much smaller values (τ or ≈ 1.6 ps at 298.15 K) of Morresi et al [12] were neglected as it appears that their estimated sample temperatures are incorrect. However, the remaining data for τ or [8][9][10]17,46] match well in magnitude and, where determined as a function of temperature [9,10], in slope (Fig. 5).…”

“…Because of its simple molecular structure and high symmetry AN is also a favourite model solvent for theoretical and simulation studies of liquid-state structure and dynamics [3][4][5][6][7][8]. Molecular reorientation in AN was probed with NMR spectroscopy [9,10] and infrared/ Raman band shape analysis [11,12], revealing that the motions can be classified as anisotropic rotational diffusion. Far-infrared [13][14][15][16] and time-resolved optical Kerr effect (OKE) spectroscopy [17] of the collective dynamics in the sub-picosecond region showed that dipole libration predominates but significant contributions from induced moments and especially cross-correlations of permanent and induced dipoles are also present [5].…”