An investigation has been made of the hydroformylation of styrene, alpha-methylstyrene, p-methyl-styrene and p-acetoxy-alpha-methylstyrene in the presence of a catalytic system containing Rh (AcAc)(CO)2 modified with triphenylphosphine and phosphite ligands of different structure at t = 80-degrees-C and P = 6 MPa (CO/H-2 = 1). The formation of catalytic forms of rhodium complexes has been studied by means of in situ IR spectral measurements. If Rh(AcAc)(CO)2 modified with triphenylphosphine is used as the catalyst, oxygen-containing substrates are inactive in hydroformylation on account of the coordination of the substrate with the rhodium atom by the oxygen atom. The use of phosphite ligands made it possible to produce active catalysts for the hydroformylation of oxygen-containing substrates. The reaction of p-acetoxy-alpha-methylstyrene catalysed by an Rh(AcAc)(CO)2 + P(OPh)3 system produced 17% isomer with a quaternary carbon atom.