USE OF N-15-H-1 AND N-15-C-13 COUPLING-CONSTANTS FOR THE MEASUREMENT OF URACIL MONOANION TAUTOMERISM

We have measured the proton and carbon-13 couplings to nitrogen-15 (JH 6,N1, JH 5,N1,JH 5,N3, and JC6,N1) for uracil-l,-3-15N2, its N-deuteriomethyl derivatives (I-IV), and the corresponding monoanionic species (Ia ⇄ Ib, IIa, and IIIb). These parameters were found to be sensitive probes for the determination of the uracil monoanion tautomeric equilibrium (Ia ⇄ Ib) by reference to the fixed tautomer models, Ila and Illb. Similar measurements were performed employing JH 5,H 6,δH6-δH 5, and δC6-δC5- The population of the N1H tautomer (Ia), based upon the weighted average derived from four of these coupling constants, is 48.5%. If a correction is made for the effect of N-methyl substituents on the tautomer models, IIa and IIIb, the weighted average is 52.2%. The above population determinations are in excellent agreement with those made previously using other methods. The potential of this approach in the study of similar equilibria for oligonucleotides is discussed. © 1979, American Chemical Society. All rights reserved.