1H and13C NMR spectra of betaines, >N+(CH2)nCOO−, and their hydrogen halides. Additivity rules for carbon-13 chemical shifts

Abstract

The 1H and 13C chemical shifts of N-methylpiperidine betaines (1), C5H10N+(CH3)(CH2)nCOO−, and their derivatives C5H10N+(CH3)(CH2)nCOOH·X− (2) and C5H10N+(CH3)(CH2)nCOOC2H5·X− (3) with n = 1–5 were identified using two-dimensional homonuclear (1H) chemical shift correlation (COSY) and heteronuclear (1H, 13C) chemical shift correlation spectroscopy (H,C-COSY). The effects of the positively charged nitrogen and COO−, COOH, COOEt groups on the methylene protons in the tether groups [N+(CH2)nCOO] and the ring protons in 1, N-methylpyrrolidine betaines (4), pyridine betaines (6) and their hydrogen halides, were analysed. Empirical additivity rules for the 13C chemical shifts of tether C-1, C-2, C-3, C-4 and C-5 atoms for 1, 4 and 6 and their hydrogen halides were derived from the experimental results. The effect of N+ on the β carbon vary with the ring type. Copyright © 2000 John Wiley & Sons, Ltd.