The structures of a series of methoxystyryl cyanoacetates have been calculated using the AM1 method. The dipole moments, transition energies, and hyperpolarizabilities of these systems calculated using a semiempirical sum-over-states approach are highly dependent on the position of the donor group. The 4-methoxy derivative shows the largest hyperpolarizability of the three possible isomers, but the presence of an additional donor oxygen at the 3-position as in the related piperonylidene cyanoacetate gives a large unexpected enhancement to the value.