31P and 1H Spin–Lattice Relaxation in Several Substituted Phenylphosphines in the Liquid State

Abstract

The temperature dependences of the 31P and 1H spin–lattice relaxation times of dichlorophenylphosphine, chlorodiphenylphosphine, and triphenylphosphine have been measured by the adiabatic fast passage method. Both dipolar and spin–rotation interactions contribute to the 31P relaxation mechanism in dichlorophenylphosphine and chlorodiphenylphosphine whereas only dipolar interactions provide the mechanism for the 1H relaxation in all three compounds studied. As the high-temperature limit of the measurements was 160°C, no spin–rotation interactions were observed for the 31P relaxation in triphenylphosphine. The calculations of the approximate potential functions for the internal rotation about the C–P bond in dichlorophenylphosphine and chlorodiphenylphosphine indicate hindered rotation and thus the spin–rotation mechanism arises mainly from spin–over-all-rotation coupling. Spin–rotation constants were estimated for 31P in dichlorophenylphosphine and chlorodiphenylphosphine from relaxation data and shielding constants. In addition to relaxation measurements, the temperature dependences of densities and viscosities of dichlorophenylphosphine and chlorodiphenylphosphine have also been measured.

Comparison of 31P Spin—Rotation Interaction Constants Derived from Chemical Shift Data and from NMR Relaxation and Viscosity Data

“…(9) gives values of Geff in reasonable agreement with isotropic chemical shift values C" obtained from Eq. (lOb) and that rather poor estimates of the average correlation times were the primary reasons for the large discrepancies found in previous studies.…”

“…Their Tl SR are then given by the total 3lp relaxation rates. At 25°C these are """'3.5 and """'9.5 sec for PCIa and POCIa, respectively.7 (1) and (2) give Ceff = (fi.12V17rI) (lITI sRD)1/2 (9) from which we now can calculate Ceff for PCIa, POCIa, and PBr3. For D we use DA, defined as tD.I.+tD 11 (Table I) and for I a similar average (Table II).…”

“…Therefore Eqs. (9) and (13) can be used with some degree of confidence on these two molecules. For the bigger phosphorous compounds studied in this paper inertial effects should be less of a worry.…”

Practical aspects of real-time reaction monitoring using multi-nuclear high resolution FlowNMR spectroscopy

“…3) leads to a faster decay of the FID under flow conditions, and faster restoration of Z-magnetisation, because nuclei with detectable magnetisation in the XY plane at the start of the acquisition period are leaving the detector before they have fully relaxed, being replaced by either fresh Z-magnetisation from nuclei in region B (if flow is relatively slow and/or T 1 relatively fast) or − , BF 4 − and PPh 3 result in unusually long relaxation times. 44,45 Fig at least partial Z-magnetisation (if flow is relatively fast and/ or T 1 is relatively slow). This out-flow effect on the effective T 1 relaxation time for different 1 H environments can be directly observed by standard T 1 measurements, with effective T 1 reductions of up to 66% at 4 mL min −1 as compared to static samples (Fig.…”