Figure 5.

Imidazolium bridge structure predicts the effects of ¹³C isotope label at C2 on NMR spectra. (a) Partial chemical structure of an activated monomer showing the location of the ¹³C isotope label two bonds from the naturally abundant ³¹P atom. (b) Partial chemical structure of the imidazolium bridge showing that the ¹³C isotope label will be split by two equivalent ³¹P atoms. (c) ¹³C NMR (100 MHz) spectrum of 50 mM ¹³C isotope labeled 2-MeImpC at pD 8.49. (d) ¹³C NMR (100 MHz) spectrum of 50 mM ¹³C isotope labeled 2-MeImpC at pD 6.93. The inset displays an observed triplet at 151.0 ppm. (e) ³¹P NMR (161 MHz) spectrum of 50 mM 2-MeImpC without the isotope label at pD 7.02. (f) ³¹P NMR (161 MHz) spectrum of 50 mM ¹³C isotope labeled 2-MeImpC at pD 6.93. Peaks from 2-MeImpC are highlighted in black and from dicytidine intermediate in red.