A compound of general formula (I) with or without the double bond illustrated by the dotted line. In formula (I), X is a CHO, CH2OH, CH2OC(O)R or CH(OR)2 group, and R represents a linear or branched C1-C5 alkyl or alkenyl chain. The synthesis method for the compound, and especially the 6,8-dimethyl-non-7-enal (1) prepared by the hydroformylation of the 5,7-dimethyl-octa-1,6-diene is also disclosed, as well as compositions containing the compounds of formula (I). Due to the odorant properties thereof, the compounds are highly useful in perfumery, especially for cosmetic products and household products.