Both were useful in making pigments and both had herbicidal properties. The structural difference between the two "closely related" compounds was that 3,4-DCAA "differ[ed] in its structural formula solely by having one less CH2 group" than 3,4-DCPA.[4] Because of the similarity in structure between 3,4-DCPA and other chemicals, including 3,4-DCAA, the Patent Office rejected the patent application on obviousness grounds. Monsanto then tried to persuade the Office to withdraw the rejection by submitting documents to show that DCPA was not obvious, because it had greatly superior and unexpected selective herbicidal activity.