The present invention relates to piperazine compounds of the general formula I defined below and to their use as herbicides. Moreover, the invention relates to compositions for crop protection and to a method for controlling unwanted vegetation. In formula I, A1, A2 independently of one another are aryl or heteroaryl, where Ra is attached in the ortho-position to the point of attachment of A1 to a carbon atom or a nitrogen atom of A1, Y1, Y2 are oxygen, sulfur or a group NRy1, and the variables Ra, Rb, Rc, Rd, Re, Rf, R1, R2, R3, R4, R5, R6, R7, and R8 have the meanings mentioned in the claims and the description.