1,3-Cyclohexadiene has been prepared by dehydration of cyclohexen-3-ol, by pyrolysis at 540° of the diacetate of cyclohexane-1,2-diol, by dehydrobromination with quinoline of 3-bromocyclohexene, by treating the ethyl ether of cyclohexen-3-ol with potassium bisulfate, by heating cyclohexene oxide with phthalic anhydride, by treating cyclohexane-1,2-diol with concentrated sulfuric acid, by treatment of 1,2-dibromocyclohexane with tributylamine, with sodium hydroxide in ethylene glycol, and with quinoline, and by treatment of 3,6-dibromo-cyclohexene with sodium.