s -1 at 298.15 K. This corresponds to a tunneling-corrected t1/2 of 1.4 hrs. On the other hand, the rapid tunneling rate kT of 2 s -1 for the forward reaction implies a t1/2 of only 0.3 s, suggesting that the P(V) oxide tautomer is too short-lived a species and that only the P(III) form should be detected under normal experimental conditions at RT, in agreement with the aforementioned experimental observation.