Final answer:
NaCl, NaBr, and KCN substrates usually indicate the mechanism of ionic compounds dissociating into ions in polar protic solvents like H₂O.
Step-by-step explanation:
The substrates NaCl, NaBr, and KCN usually indicate the mechanism of ionic compounds dissociating into ions in polar protic solvents like H₂O. This is because polar protic solvents solvate both cations and anions, allowing for the dissociation of the substrate. On the other hand, polar organic compounds like H-Br and H₂C-Br have less tendency to dissociate in these solvents. However, tertiary substrates like (H3C)3 C—Br can still dissociate due to the strong effect of steric crowding and the ability of the polar protic solvent to solvate them.