Abstract: A method to synthesize a fatty nitrile/ester aldehyde comprising the following steps: 1) hydroformylation of a ?-unsaturated fatty nitrile/ester/acid substrate under particular conditions of partial pressure, temperature, reaction time, conversion rate of the ?-unsaturated fatty nitrile/ester/acid reactant, catalyst, [substrate]/[metal] molar ratio and [ligand]/[metal] molar ratio so as after the reaction to obtain: a hydroformylation product comprising at least one fatty nitrile/ester/acid aldehyde of formula: OHC—(CH2)r+2—R, and an isomerate comprising at least one fatty nitrile/ester/acid isomer with internal unsaturation in which at least 80% of the internal isomer(s) of the isomerate are formed of the ?-1 unsaturated isomer of formula CH3—CH?CH—(CH2)r?1—R; followed by: 2) separation and recovery of the fatty nitrile/ester/acid aldehyde and of the isomerate.