A simple kinetic method has been applied to measure the formation constants of aqueous copper(l) with fumaronitrile, dimethyl fumarate, and fumaric and maleic acids, At 0.14 M ionic strength, the values of beta(1) are (0.85 +/- 0.02) x 103, (6.1 +/- 0.1) x 10(3), (7.3 +/- 0.1) x 10(3), and (2.2 +/-0.4) x 10(3) M-1, respectively. The values for the last two olefins are compared to previous results. Values of beta(1) for hydrogen maleate and beta(2) for fumaronitrile also have been determined. A reanalysis of much earlier work has been done, and all the results are discussed in terms of the effect of substituents on the olefin on the beta(1) values. The structure of bis(fumaronitrile)copper(l) nitrate also is reported. The nitrile is N-coordinated to copper(l), which has a distorted tetrahedral geometry, while the overall structure consists of macrocyclic Cu-6(fumaronitrile)(6) rings which extend in three dimensions.