The tautomerism of oxalamidine, wich consists of an intramolecular degenerate double proton transfer between nitrogen atoms, has been studied by dynamic NMR spectroscopy. Experiments were performed on two bicyclic oxalamidines, 2,2’-bis(3,4,5,6-tetrahydro-1,3-diazine) (OA6) and 2,2’-bis(4,5,6,7-tetrahydro- 1,3-diazepine) (OA7) dissolved in organic solvents. For this purpose, both compounds had to be labeled with N-15 and partly with H-2. The tautomerism of OA6 was too slow to be detectable by NMR, in contrast to the case of OA7. Rate constants of the tautomerism of OA7 dissolved in methylcyclohexane-d(14)(MCY) and in acetonitrile d(3) (AN) could be obtained, including the full kinetic HH/HD/DD isotope effects. Tile data for MCY can be represented by the following : k(MCY)(HH)=10(11.2+/-0.1) exp(-57.6 +/- 06 kJ mol(-1)/RT) s(-1), 303K less than or equal to T less than or equal to 415 K, k(298 k)(HH)=14 s(-1); k(MCY)(HD)=10(11.1+/-0.1) exp(-59.6 +/-1.0 kJ mol(-1)/RT) s(-1), 340 K less than or equal to T less than or equal to 415 K, k(298 K)(HD)=4.4 s(-1); k(MCY)(DD) =10(10.9+/-0.1) exp(-59.5 +/- 0.7 kJ mol(-1)/RT) s(-1), 303 K less than or equal to T less than or equal to 415 K, k(298 K)(DD)=2.9 s(-1). From these data, we determine that k(MCY)(HH)/k(MCY)(HD)approximate to 3.1, k(MCY)(HH)/k(MCY)(DD)approximate to 4.8, and k(MCY)(HD)/k(MCY)(DD)approximate to 1.5 at 298 K. The data for AN are as follows : k(AN)(HH)=10(11.7+/-0.1) exp(-56.2 +/- 0.9 kJ mol(-1)/RT) s(-1), 300 K less than or equal to T less than or equal to 382 K, k(298 K)(HH)=75 s(-1); k(AN)(HD)=10(11.5+/0.1) exp(-57.6 +/- 1.4 kJ mol(-1)/RT) s(-1), 312 K less than or equal to T less than or equal to 374 K, k(298 K)(HD)=23 s(-1); and k(AN)(DD)=10(11.1+/-0.2) exp(-56.7 +/- 1.2 kJ mol(-1)/RT) s(-1) 300 K less than or equal to T less than or equal to 393 K, k(298 K) 15 s(-1). From these data, we determine that k(AN)(HH)/k(AN)(HD) = 3.2, k(AN)(HH)/k(AN)(DD)=5.2, k(AN)(HD)/k(AN)(DD)=1.6, and k(AN)(HH)/k(MCY)(HH)=5.4 at 298 K, No dependence of chemical shifts nor of rate constants on concentration was observed, which indicates that OA7 is not subject to intermolecular hydrogen bonding. : k(MCY)(HH)=10(11.2+/-0.1) exp(-57.6 +/- 06 kJ mol(-1)/RT) s(-1), 303K less than or equal to T less than or equal to 415 K, k(298 k)(HH)=14 s(-1); k(MCY)(HD)=10(11.1+/-0.1) exp(-59.6 +/-1.0 kJ mol(-1)/RT) s(-1), 340 K less than or equal to T less than or equal to 415 K, k(298 K)(HD)=4.4 s(-1); k(MCY)(DD) =10(10.9+/-0.1) exp(-59.5 +/- 0.7 kJ mol(-1)/RT) s(-1), 303 K less than or equal to T less than or equal to 415 K, k(298 K)(DD)=2.9 s(-1). From these data, we determine that k(MCY)(HH)/k(MCY)(HD)approximate to 3.1, k(MCY)(HH)/k(MCY)(DD)approximate to 4.8, and k(MCY)(HD)/k(MCY)(DD)approximate to 1.5 at 298 K. The data for AN are as follows : k(AN)(HH)=10(11.7+/-0.1) exp(-56.2 +/- 0.9 kJ mol(-1)/RT) s(-1), 300 K less than or equal to T less than or equal to 382 K, k(298 K)(HH)=75 s(-1); k(AN)(HD)=10(11.5+/0.1) exp(-57.6 +/- 1.4 kJ mol(-1)/RT) s(-1), 312 K less than or equal to T less than or equal to 374 K, k(298 K)(HD)=23 s(-1); and k(AN)(DD)=10(11.1+/-0.2) exp(-56.7 +/- 1.2 kJ mol(-1)/RT) s(-1) 300 K less than or equal to T less than or equal to 393 K, k(298 K) 15 s(-1). From these data, we determine that k(AN)(HH)/k(AN)(HD) = 3.2, k(AN)(HH)/k(AN)(DD)=5.2, k(AN)(HD)/k(AN)(DD)=1.6, and k(AN)(HH)/k(MCY)(HH)=5.4 at 298 K, No dependence of chemical shifts nor of rate constants on concentration was observed, which indicates that OA7 is not subject to intermolecular hydrogen bonding.