This work presents ferrate­(VI) (FeVIO4 2–, FeVI) oxidation of a wide range of sulfonamide antibiotics (SAs) containing five- and six-membered heterocyclic moieties (R) in their molecular structures. Kinetics measurements of the reactions between FeVI and SAs at different pH (6.5–10.0) give species-specific second-order rate constants, k 5 and k 6 of the reactions of protonated FeVI (HFeO4 –) and unprotonated FeVI (FeVIO4 2–) with protonated SAs (HX), respectively. The values of k 5 varied from (1.2 ± 0.1) × 103 to (2.2 ± 0.2) × 104 M–1 s–1, while the range of k 6 was from (1.1 ± 0.1) × 102 to (1.0 ± 0.1) × 103 M–1 s–1 for different SAs. The transformation products of reaction between FeVI and sulfadiazine (SDZ, contains a six-membered R) include SO2 extrusion oxidized products (OPs) and aniline hydroxylated products. Comparatively, oxidation of sulfisoxazole (SIZ, a five-membered R) by FeVI has OPs that have no SO2 extrusion in their structures. Density functional theory calculations are performed to demonstrate SO2 extrusion in oxidation of SDZ by FeVI. The detailed mechanisms of oxidation are proposed to describe the differences in the oxidation of six- and five-membered heterocyclic moieties (R) containing SAs (i.e., SDZ versus SIZ) by FeVI.

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High-resolution spectral studies of the benzoic acid dimer in host single crystals have been made to investigate the details of the changes in H bonding which occur upon electronic excitation. The principal host crystal used was benzene. An increase of H-acceptor ability in the first singlet state is shown by an anomalous H-isotope shift (a red shift upon deuteration). The occurrence of odd parity dimer modes in fluorescence also supports this conclusion. No odd parity modes appear in phosphorescence, demonstrating that the triplet state is not like the singlet. It is concluded that the triplet H bonding is not very different from that in the ground state while the singlet is forced into an unsymmetrical structure in the vicinity of the H bonds.

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