The calculated parameters of the steric and electronic structure and shielding constants of eta (2)- (3-penten-2-one)Fe(CO)(4), eta (2)-(3-penten-2-one)M(CO)(5), eta (4)-(3-penten-2-one)Fe(CO)(3), and eta (4)-(3-penten-2-one) M(CO)(4) (M = Cr, Mo, W) nicely agree with the experiment. Coordination of the alpha -enone with transition metals significantly distorts the conjugation between the C=C and C=O bonds.