Solution NMR JHD Coupling and Isotope Effects

Another dynamic process involves tautomeric equilibriahetwcea Hj and dihydride forms in solution in about a dozen complexes, including W(CO)3(PR3)2(H2) 

90-MHz continuous-wave instrument (t = 10 — 5). 7hd for HD gas is 43 Hz, the maximum value (d D = 0.74A). A lower value represents a proportionately shorter HD- - HD determined in solution correlates with dmj in the solid state via the 

According to Hush, is proportional to the H-H bond order, described 

This does not take into account magnetic couplings in trans dihydrides, where Phh is near zero. Grundemann adds a two-bond term proportional to the square of the M-H bond order, to calculate Jn- for all isotopes L, L = H, D, T (Eq. 5.6, where is the gyromagnetic ratio of L). 

The validity of Eq. (5.6) is shown in Eigure 5.7, where the solid line represents Eq. (5.6) and the points correspond to experimental data for the isotopic pairs HD (circles), HT (square), and HH (triangles). The are taken from neutron data (for hh 2 a, see below) or good-quality X-ray data (for djo — 2-3 A). The agreement 

Another dynamic process involves tautomeric equilibria between H2 and dihydride forms in solution in about a dozen complexes, including W(CO)3(PR3)2(H2) (l).47 The dihydride tautomer (2) exists in about 20% concentration in Eq. (5.2) for 

228 ppm for d(H2D) — 5(H3) at 215 K, which decreases to 0.112 ppm at 281 K.55 Over the same temperature range, the averaged JHD varies from 6.87 to 7.63 Hz for the dj species, but is essentially invariant with temperature for the d2 system (8.75 Hz). Thus there is a nonstatistical site preference for the deuterium isotope that varies with the degree of deuteration [Eqs. (5.8) and (5.9)]. 

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