Electronic structure oximes

An extensive analysis of the effect of lone pairs on the nitrogen atom on spin-spin coupling constants is reviewed in the context of a description of molecular electronic structure. Several oximes are analyzed in studies of these effects and their relevance for structural determination has been pointed out. 

The symmetry of transformation (107) is identical to that of the alkyl car-bonyl-to-acyl conversion, (5), and therefore the difference in the propensities of these insertions to occur must relate to differences in the orbital energetics of the two processes. Since the metal-nitrosyl jr-interaction is a dominant feature of the electronic structure in NO+ complexes, and since it will be weakened by the formation of a nitroso species, one can expect (107) to be correspondingly less favorable than acyl formation in (5). If reaction (107) does occur, however, one can readily envisage tautomerism of the nitroso ligand to an oxime. The reactive nature of the oxime may then create difficulties in the identification and isolation of organonitrogen products, and indeed, this may have obscured general observation of transformation (107) in the past. 

The chemical shifts of carbon atoms in NMR spectra of the oximes having pyrrolyl, furyl, benzofuryl, thienyl and pyridyl substituents change specifically on going from the E- to the Z-isomer. This makes it possible to use the chemical shifts for assignment of the oximes configuration and studying the special features of their electronic structure (08CHE1238). 

This is presumably the only example of an orthocarbonic acid derivative formed by addition of CO2 to the oxime groups. Unfortunately the electronic structure of [Ni(L1833)] has not yet been studied. According to X-ray diffraction results nickel has the formal oxidation state of zero. 

Closely related to these compounds are the lithium derivatives of imines and oximes. Their structures and stereochemistry, electronic structures, aggregation, and reactions have been extensively studied computationally. " ... 

C-Nitroso compounds, oximes, N-hydroxyguanidines and N-hydroxyureas each contain an N-O bond and release nitric oxide (NO) or one of its redox forms under some conditions. The nitrogen atom of a C-nitroso compound formally exists in the +1 oxidation state, the same oxidation state as nitroxyl (HNO), the one-electron reduced form of N O. The nitrogen atoms of oximes, N-hydroxyguanidines, and N-hydroxyureas each formally exist in the -1 oxidation state, the same oxidation state as hydroxylamine. Consequently, the direct formation of NO (formal oxidation state = +2) from any of these species requires oxidation, one electron for a C-nitroso compound and three electrons for an oxime, N-hydroxyguanidine or N-hydroxyurea. This chapter summarizes the syntheses and properties, NO-releasing mechanisms and the known structure-activity relationships of these compounds. 

Iminomethyl-l-phenyl-l,2,3-triazoles (106, R = CH3) and their structural isomer 4-(iminophenyl)-l-methyl-l,2,3-triazole (108, R = CH3) are interconvertible when they are heated in DMSO at 80°C (Scheme IV.43) (84JHC627 89JHC701 90JHC2021). The equihbrium position is dependent on the electronic properties of the substituent R. When R is alkyl, a benzyl or anisyl compound 108 is favored when R is p-chlorophenyl or p-nitrophenyl, 106 is the favored isomer. The hydrazone 106 R = NH2) or oxime 106 R = OH) do not rearrange. A diazoimine 107 can be postulated as intermediate, a species whose structure is similar to the one proposed... 

Examples of the application of correlation analysis to oxime and hydroxamic acid pK data sets are considered below. In the best of all possible worlds all data sets have a sufficient number of substituents and cover a wide enough range of substituent electronic demand, steric effect and intermolecular forces to provide a clear reliable description of the kind and magnitude of structural effects on the property of interest. In the real world this is often not the case. We will therefore try to show how the maximum amount of information can be extracted from small data sets. 

Microwave spectroscopy often gives more definite and precise information on the structure of polyatomic molecules than vibration-rotation and electronic spectra. For example, consider the simplest oxime formald-oxime, CH2=NOH. There are two likely structural configurations for this... 

Little information is available concerning the reaction of oximes with silver(I) salts.165 syn-Phenyl-2-pyridylketoxime (syn-PhC(=NOH)C5H5N HPPK) has been reported to react with silver nitrate in ethanol-water to form Ag(HPPK)2N03 (white salt, m.p. 190-191 °C). On the basis of IR and electronic spectra it was concluded that the structure was linear with only the pyridyl N atoms being bound to the Ag+ ion.166... 

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