Puzzling Compounds

Six puzzling compounds, macusine C, rauvolfinine, dihydrotalpinine, alkaloid Q3, ll-methoxy-jVa-methyldihydropericyclivine, and neosarpagine, that persistently appeared in earlier reviews as sarpagine derivatives are excluded from Tables I and II. Their history and the reasons for their rejection are noted next. 

The case of i-methyl-4-quinolone is puzzling. The large proportion of the 3-nitro isomer formed in the nitration (table 10.3 cf. 4-hydroxyquinoline) might be a result of nitration via the free base but this is not substantiated by the acidity dependence of the rate of nitration or by the Arrhenius parameters. From r-methyl-4-quinolone the total yield of nitro-compounds was not high (table ro.3). 

The substituted 1,2,3,4-letrahydroisoquinolines studied by Knabe and Roloff (87) also produce some puzzling results difficult to rationalize when oxidized with mercuric EDTA. Compounds 88 and 89 are not attacked to... 

An understanding of covalent hydration is essential for all who work with heteroaromatic compounds containing doubly bonded nitrogen atoms. As chemists become more aware of the circumstances in which hydration occurs, and the means for detecting it, many new examples will probably be discovered and many puzzling discrepancies solved. Many of the values for ionization constants and ultraviolet spectra which are in the literature refer to partly hydrated equilibrium mixtures and should be replaced by values for the pure substances. 

The label on my shampoo bottle listed many compounds, and, due to my interest in chemistry, most of them were familiar or had obvious functions. However, one compound stood out as puzzling sodium chloride. 

Not all observations are summarized by laws. There are many properties of matter (such as superconductivity, the ability of a few cold solids to conduct electricity without any resistance) that are currently at the forefront of research but are not described by grand laws that embrace hundreds of different compounds. A major current puzzle, which might be resolved in the future either hy finding the appropriate law or by detailed individual computation, is what determines the shapes of big protein molecules. Formulating a law is just one way, not the only way, of summarizing data. 

The moments of complexes containing NO offer a puzzling problem. The diamagnetism of compounds of iron and ruthenium suggests that Feiv and RuIV form a double bond with NO, making seven bonds in all, which woud lead to /t = 0. But this structure cannot be applied to [Co(NH3)6-NO]Cl2, which has a moment corresponding to a triplet state. Further study of such complexes is needed. 

Only in recent years has progress been made in attacking the problem presented by these intermetallic compounds at the present time we may say that, although there are a number of puzzling questions that remain unanswered, the beginning of a theory of the stability and other properties of the substances has been formulated. 

In the course of the further investigation of resonating valence bonds in metals the nature and significance of this previously puzzling unstable orbital have been discovered, and it has become possible to formulate a rational theory of metallic valence and of the structure of metals and intermetallic compounds. 

However, more recently, a functionally selective inhibitor of nNOS has been described — 7-nitroindazole (7-NI). It is puzzling that in vitro this compound has no selectivity for nNOS over eNOS but after systemic administration, fails to change blood pressure yet alters neuronal responses that are thought to result from production of NO. A suggested resolution of this action is that 7-NI is metabolised in the periphery but not the CNS, so that once it has crossed the blood-brain barrier, it can only act on nNOS. 

Silver(I) complexes are known with the tris(pyrazolyl)borate [HB(pz)3] and the methyl, phenyl, bromo, or trifluoromethyl-substituted derivatives. The structure of the silver tri(pyrazolyl)borato species has been a puzzle since it was first reported.385,386 It was suggested that the structure could be oligomeric, but recently the crystal structure of the compound [Ag HB(3,5-Me2pz)3 ]2 shows that it has a dimeric structure387 where the silver(I) centers are tricoordinated by a bidentate arm of one ligand and a monodentate arm of the other ligand (29). The related complexes [Ag HB(4-Brpz)3 ]2, [Ag HB(4-Mepz)3 ]2, [Ag HB(3,5-Me2pz)3 ]2, [Ag HB(3-Mepz)3 ] , [Ag B(pz)4 ], and... 

The arrangement remains puzzling, but the bees easily resolve the problem (or what we see as a problem). When the parasitic bees mate, the male simply sprays some of his F6 on the female. The compound is relatively involatile and so persists on the gravid female as she seeks host nests for her eggs. Perfumed with F6 from her mate, the parasitic female penetrates the host nest and completes her task unchallenged. At least three other species of parasitic Nomada bees gain acceptance by their Andrena hosts in this way. 

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