An acetal of formula I: ##STR00001## is described in which the radicals R.sup.1 to R.sup.6 independently of one another are eac hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl, n=0 or 1, and there is a single bond or double bond at the location of a broken line between two C atoms, any double bond present in the chain linking the aliphatic ring to the acetal group having the E or Z configuration, with the proviso that the number of double bonds incorporating a C atom of the aliphatic ring is 0 or 1, and the number of double bonds not incorporating a C atom of the aliphatic ring is 0 or 1.