Abstract The infrared absorption of the carbonyl peak of acetylcholine exhibits a shift toward the higher energy. 2-Dimethylamino ethyl acetate, 3-dimethylaminopropyl acetate, 4-dimethylaminobutyl acetate show the expected absorption spectra for the carbonyl peak in that they are precisely like ethyl acetate. 3-Dimethylaminopropyl acetate methiodide and 4-dimethylaminobutyl acetate methiodide do not exhibit absorption for the carbonyl peak like acetylcholine, but rather behave like the unquaternized esters. dl, cis 2-Dimethylamino-cyclohexanol acetate methiodide shows a similar shift in the infra-red absorption for the carbonyl peak of acetylcholine, the trans isomer does not. The above evidence was advanced in support of a cyclic conformation of acetylcholine which can explain the observed kinetic data for alkaline hydrolysis and acid catalysis of this substance, as well as explain the rates of acylation of hydroxylamine observed.