Oximes protonation

The favourable intra-molecular hydrogen-bonding between the oxime proton and the phenol oxygen atom will reduce or overcome liganddigand repulsion enthalpy terms normally involved in the formation of bis-chelate complexes. The integrity of this head-to-tail macrocyclic assembly is preserved in c/.v-octahcdral complexes which are formed in the presence of a, co-diamines. [66, 67]... 

Hydrolysis of cyclohexane-1,2,3-trione-l,3-dioxime (23, X = O) and its 2-imine (X = NH) has been studied in perchloric acid solution.91 The mechanism is proposed to involve a protonation pre-equilibrium, followed by slow water addition to protonated and non-protonated forms. Oxime protonation pXas have been calculated. 

The [TcO]3+ core is sufficiently electron deficient to deprotonate secondary aliphatic amines, and in 36 and analogs neutrality is achieved by loss of both amine protons and one oxime proton, with the remaining oxime proton being intramolecularly hydrogen bonded. Features of the structures are Tc=0 bond distances in the range 1.670(4)-1.682(5) A and the displacement of Tc above the N4 plane, which for 36 is 0.678(1) A. Also, for 36 the distance between Tc and the deprotonated N (imino) atoms of 1.913 A (av.) is considerably shorter than the Tc-N(oxime) distance of 2.090 A (av.) (453). The y(TcO) IR absorption in the rather... 

The synthesis of organocobaloximes via Grignard reactions is exemplified in the following preparation of phenyl(pyridine)-cobaloxime. Since the cobalo.ximes contain two acidic oxime protons, the Grignard reagent must be employed in threefold... 

The standard H NMR spectrum of compound 1 in C6D6, part of which (the resonance area of the oximic proton singlets) is shown in Figure 15(a), reveals numerous resonances with various intensities. While die low intensity resonances are difficult to analyse, the high intensity patterns are in agreement with the structure of Figure 14, as they reveal, in particular, three butyl methyl resonances (not shown) and two oximic proton resonances (Figure 15a), associated with a major species, hereafter M. 

Figure 21 Structure proposed for species m2 (R = n-butyl). A scheme for the "7( Sn, H) coupling pattern observed in the 2D HMQC spectrum in the oximic proton region of m2 is displayed on the right. (Reproduced with permission from ref. 17)...

The symbol H-, (H 2, etc.) is used to represent the ionization of one (two, etc.) amide protons or oxime protons from the metal complex. In the pyrimidine and purine sections, it is also used for the ionization of a proton from the ligand alone at high pH. 

The oxime proton is sufficiently acidic that it can be titrated to give the conjugate base, as in equation (4), and it is possible to consider the relative reactivities of the neutral (19) and deprotonated (20) complexes in hydrol-... 

The inflection of the Ej/2 -pH plot was attributed [84] to the existence of two forms of these oximes protonated in different ways, and this conclusion was confirmed by isolation of the products from electrolysis at controlled potential. 

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