There are innumerable instances of series conforming to linear free energy relationships (LFERs) in the literature and appreciable numbers of examples of non-conformity. It is extremely rare or maybe we are the first to report conformity and non-conformity of Hammett’s relationship (LFER) in the same system, the para-substituted phenyl pentazoles. This rarity and a plausible rationale are discussed. This research article requires a good understanding of Hammett’s relationship (LFER), harmonic oscillator model aromaticity (HOMA index) and bond length alternation (BLA). (Image credit: Sanjeev Rachuru.)

This review summarises the applications of hydroxamic acids in medicinal chemistry, mineral flotation, metal–organic frameworks (MOFs), remediation of metal contamination and more, and introduces related synthesis strategies including microwave, continuous flow reactor, solid-phase and enzymatic syntheses as supplements to classical synthetic methods. (Image credit: Li Yao.)