Theoretical studies of 1H, 13C and 15N NMR spectra for model structures of n-methylmorpholinium and N-methylpiperidinium betaines

Screening constants for model structures of linear and twisted conformers of N-(omega-carboxyalkyl)-N-methylmorpholinium inner salts (MMBn) and N-(omega-carboxyalkyl)-N-methylpiperidinium inner salts (MPBn) with the alkyl spacer (n) containing 1-5 methylene groups calculated by the GIAO/B3LYP/6-31+G(d, p) are reported and analyzed. Linear correlations between the experimental 1H and 13C chemical shifts and computed absolute shielding constants have been obtained. These results suggest that in solution twisted conformers dominate. The linear correlations between the calculated 15N absolute shielding constants for MMBn and MPBn suggest that the two kinds of betaines have similar structures.