Simultaneous conformity and non-conformity to Hammett’s linear free energy relationship (LFER): a rarity

Linear free energy relationships (LFERs) are an important topic in physical-organic chemistry. When one browses the literature, one encounters innumerable instances wherein the series in question conforms to LFER; one also encounters appreciable numbers of examples of non-conformity to LFER. It is extremely rare or maybe we are the first to report simultaneous conformity and non-conformity of Hammett’s relationship (LFER) in the same series, the para-substituted phenyl pentazoles. This rarity and a plausible reason are discussed.