In an effort to circumvent existing drug laws, novel psychoactive substances are continuously being developed. The stimulant benzylpiperazine (BZP) is one such "designer" recreational drug. The synthesis of these compounds is not carefully controlled, so the drugs often contain reaction by-products, and dibenzylpiperazine (DBZP) has been found (J. Chromatogr. A 2015, 1397, 32–42.) as a contaminant in samples of BZP. For each of the following compounds, consider the four CH2 groups in the nitrogen-containing ring (called a piperazine ring), and identify any chemically equivalent protons.