Solvent effects in the 2JHH, 3JHH, 1JNC and 2JNC coupling constants in the NMR spectrum of acetylcholine chloride

Coupling constant values (JNH and JNC) obtained from 1H and 13C NMR spectra of acetylcholine chloride (ACh) in several solvents with a wide range of permittivity constants (ε) are remarkably invariant, indicating the absence of solvent effects in the conformational equilibrium of this compound. The values show that the OCH2CH2N+ system occurs in a gauche arrangement. JNH and JNC are observable in most solvents, but not in chlorine-containing solvents, and are not dependent on solvent viscosity. This behavior was explained using data from T1 measurements. The measurement of NMR diffusion coefficients shows that ACh has a greater tendency to aggregate when dissolved in chlorinated solvents, a fact that could explain the observed differences in 14N T1.