The mechanism of racemisation of 1-trans-αγ-dimethyl-glutaconic acid has been discussed by Thorpe in his Presidential Address to the Chemical Society (J.C.S., (1931) 134, 1011) where he suggests that the glutaconic acids are an example of cis-trans stereoisomerism modified by the special conditions attached to three carbon isomerism considered on the modern ionisation theory. Packer and Thorpe (J.S.C. (1926) 129, 1199) arrived at the conclusion that in symmetrically αγ-substituted glutaconic acids isomeric forms underwent the following changes – [Diagram] Since there is a tendency for like groups to take up positions as far apart as possible the traps form will show a greater tendency to interconversions (racemisation) than will the cis forms and this change may occur to the entire exclusion of the cis forms. Tautoneric change in the three-carbon system is represented by Thorpe as taking place by the removal of the mobile hydrogen ion as proton, giving a symmetrical glutaconic ion (III) which is probably only a passing phase in electromerisation.