containing from 1 to six carbon atoms; and R4 is a hydrogen atom or an alkyl group containing from 1 to 3 carbon atoms; and with the proviso that R1 and R4 cannot simultaneously be hydrogen, and further with the proviso that R2 and R3 cannot simultaneously be hydrogen and wherein the bonds designated by () represent that the compound can be in the cis- or trans- isomer configuration. 2.