Proton chemical shift data have been used in three ways to estimate the aromatic character of the 2-pyridone ring. The results are reasonably consistent and indicate that 2-pyridones have ca. 35% of the aromaticity of benzene, as defined by ability to sustain an induced ring current. The formally related 1,2-dihydro-2-methylenepyridine system is not aromatic : this conclusion has bearing on the constitution of adducts from pyridine and 3-picoline with acetylenedicarboxylic ester.* It is emphasised that (A) and (B) are fixed-bond model structures.aza-cyclohexatriene, and is not meant to represent a hybrid structure.
1 : 3-Di-iminoisoindoline readily reacts with 2 : 6-diaminopyridine, to give a red compound, C,,H,,NS. The structure of this has been established as ( 11) by analytical and synthetical evidence. It contains a cross-conjugated macrocyclic system of a novel type, related to some extent to the azaporphins. The macrocyclic compound forms metallic derivatives of high thermal stability, in which the metal occupies the centre of the ring. Lightabsorption data are discussed.
Reaction of the title ligand (L) with copper salts leads to the formation of three principal series of compounds, LCu2X3(OH)•H2O (X = Cl, Br), LCu2(RCO2)3, and LCu2(RCO2)4, where RCO2 represents various aliphatic and aromatic carboxylate species. Magnetic data, electronic spectroscopic data both at room temperature and at −196 °C, infrared spectra, and microanalytical data are correlated to reveal that these complexes contain a binuclear copper-copper system in which the copper atoms are 5-coordinate and square pyramidal. Brief details are presented of an X-ray structural analysis of the chloride complex confirming the structure proposed.The ligand forms complexes both in its neutral form and in an anionic deprotonated form. The ultraviolet spectra of the complexes distinguish these modes of bonding. The electronic spectra are discussed in terms of the 5-coordinate square pyramidal copper chromophore deemed to be present. In the complex L2Cu, the copper atom has a trigonally distorted 6-coordinate environment with tridentate anionic ligand.
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