AbstractA comparison of calculated and experimental data shows that the optical rotatory power of phenylallenecarboxylic acids is quantitatively described by the polynomial expression developed in (1). The Tdcomponent of this expression, the only relevant one for the case of methane derivatives turns out to be negligibly small in the case of allene derivatives. Therefore, and because allene derivatives belong to category a[16]the sequence of the λ‐parameter values of the ligands may be used to determine the configuration and the sign of rotati