Classical bioisosteres are functional groups that satisfy with the Grimm's hydride displacement law and Langmuir's definition of isosteres.
My question is why chlorine can be replaced by trifluoromethyl or cyano group and the replacement is categorized in univalent atoms replacement?
Because as seen from the criteria of classical bioisosteres aforementioned, the replacement atoms do not have any hydrogen atom therefore I think Grimm's law is devoid. However both trifluoromethyl and cyano group do not have the same number of atom nor electron as well as electron arrangement as in chlorine.
So what explains that these functional groups are classical bioisosteres?