Solvent effects on N-15 NMR chemical shifts of 2,6-di-tert-butylpyridine. Absence of hydrogen bonding with the nitrogen atom

Comparison of the (SN)-S-15 chemical shifts of 2,6-di-tert-butylpyridine (D TBP) and pyridine (Py) in a series of solvents demonstrates the inability o f the nitrogen atom in DTBP to participate in hydrogen bonds. Both bases ar e fully hydronated in trifluoromethanesulfonic acid (TFMSA) and trifluoroac etic acid (TFA) solutions, but the chemical shift values for Py differ in t he two media, indicating hydrogen bonding between the N-H group of the pyri dinium ion and the trifluoroacetate anion in the ion pair, which is absent in hydronated DTBP.