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

Abstract

Comparison of the ¹⁵N chemical shifts of 2,6-di-tert-butylpyridine (DTBP) and pyridine (Py) in a series of solvents demonstrates the inability of the nitrogen atom in DTBP to participate in hydrogen bonds. Both bases are fully hydronated in trifluoromethanesulfonic acid (TFMSA) and trifluoroacetic acid (TFA) solutions, but the chemical shift values for Py differ in the two media, indicating hydrogen bonding between the N–H group of the pyridinium ion and the trifluoroacetate anion in the ion pair, which is absent in hydronated DTBP.