The biologically active Michael acceptor 2-methylene-3-quinuclidinone (MQ) has a unique chemical reactivity and forms several products upon dissolution in water. With the use of X-ray, NMR and LCMS data the structures of two previously incorrectly characterised compounds are rectified. A complex equilibrium in water, containing novel dimeric species of MQ, and its dependence on temperature, pH and concentration is presented.