Therefore, we can assign proton 10 as 5.209 ppm and proton 11 as 3.754 ppm. To differentiate protons 10 and 11, take a look at our COSY table 3.754 ppm shows two COSY correlations, while 5.209 ppm only shows one. From this list, we can easily assign proton 8 as the peak at 2.068 ppm based on its integration of 2 protons. Based on the COSY, proton 9 couples protons at 2.068 ppm (2H), 3.754 ppm (1H), and 5.209 ppm (1H). Thymidine’s structure suggests that proton 9 should couple protons 8, 10, and 11. Now that proton 9 has been assigned, the fun really begins. The remaining protons are doublets, triplets, and multiplets that can be assigned by 2-dimensional COSY. The peak also integrates to 1 proton, supporting the assignment. The chemical shift of 11.256 ppm supports this assignment, as imide protons often show up far downfield. The only proton that should show up as a singlet is proton 6, as it has no neighboring protons that would split the peak (the nearest proton is 5 bonds away!). There is only one singlet in the ¹H-NMR spectrum. Therefore, the peak at 7.690 ppm must represent proton 4! The integration and chemical shift support the assignment, as proton 4 is the only aromatic proton in the structure. The long-range coupling constant observed for proton 3 (J=1.2 Hz, split into a doublet by proton 4) is reflected in the coupling constant for proton 4 (J=1.2 Hz, split into a quartet by proton 3). Protons that are coupled to each other should exhibit the same coupling constant. The peak is split into a doublet with a coupling constant of 1.2 Hz, reflecting the long-range coupling between protons 3 and 4, which also supports this assignment. The high field chemical shift supports this assignment. The only peak with an integration of 3 is the doublet at 1.770 ppm. Proton 3 is the only methyl group in the structure, and therefore must integrate to 3 protons.
0 kommentar(er)
