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

Coupling constant values ( J_NH and J_NC) obtained from ¹H and ¹³C NMR spectra of acetylcholine chloride (ACh) in several solvents with a wide range of permittivity constants ( ɛ) are remarkably invariant, indicating the absence of solvent effects in the conformational equilibrium of this compound. The values show that the OCH ₂CH ₂N ⁺ system occurs in a gauche arrangement. J_NH and J_NC 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.