Ionisation isomerism

Isomerism in the Metal-ammines.—Werner claimed for the coordination theory that in certain cases isomerism should occur, that isomerism being brought about by different causes. lie divided isomerism in the ammines into five groups, namely, structure isomerism, ionisation isomerism, hydrate isomerism, polymerism, and stereoisomerism. 

Ionisation Isomerism.—This type of isomerism is very common in the metal-ammines. If two or more different acidic radicles are present in a molecule of metal-ammine, the acidic radicles may be firmly fixed in the co-ordination complex or may be outside of this. If they are outside the complex they are easily ionised and easily freed by other acids if, on the other hand, they are within the complex they are not ionised and are difficult to free by other acids. This distribution of the acidic radicles in the complex, or outside of it, gives rise to ionisation isomerism. Tor example, the compound Co(NH3)5Br(S04) is known in two forms, one violet and the other red. The violet modification in aqueous solution contains —S04" ions, which may be precipitated by barium chloride. The red variety gives no — S04" ions in aqueous solution, and barium sulphate is not precipitated by barium chloride. These two substances, bromo-pentammino-eobaltic sulphate and sulphato-pentammino-eobaltic bromide, are ionisation isomers, and are represented as ... 

Ionisation Isomerism.—This is shown in the chromic hydrates, ehloro-pentaquo-chromic sulphate, [Cr(H20)5Cl]S04, and sulphato-pentaquo-chromic chloride, [Cr(H20)BS04]Cl.(l... 

Isomerism in Metal-Ammines—Structure Isomerism—Ionisation Isomerism— Hydrate Isomerism—Polymerism—Stereo-isomerism. 

Werner also described and named the various other types of isomerism observed in coordination compounds. These are ionisation isomerism, displayed by [Co(NH3)5C1]S04 and [Co(NH3)5S04]Cl hydrate isomerism, for example [Cr(H20)5]Cl3 and [Cr(H20)5Cl]Cl2.H20 and coordination isomerism, which occurs when both cation and anion are complexes, for example [Co(NH3)5][Cr(CN)6] and [Cr(NH3)5][Co(CN)6] Werner also explained one case of what is now known as linkage isomerism in [Co(NH3)5N02]Cl2 and [Co(NH3)50NO]Cl2, where the NO2 ligand has two possible sites of attachment to the metal atom. It was many years before other linkage isomers were prepared. 

These reactions involve the intermediate formation of thiols, followed by condensation to the sulfides. The observation of isomerized products in suitable cases indicates the intermediate formation of carbocations, either by protolysis of alkanes by the superacid or reversible ionisation of the thiol products (149). 

The homologues of the methylated non-ionic EO/PO surfactant blend were ionised as [M + NH4]+ ions. A mixture of these isomeric compounds, which could not be defined by their structure because separation was impossible, was ionised with its [M + NH4]+ ion at m/z 568. The mixture of different ions hidden behind this defined m/z ratio was submitted to fragmentation by the application of APCI—FIA—MS— MS(+). The product ion spectrum of the selected isomer as shown with its structure in Fig. 2.9.23 is presented together with the interpretation of the fragmentation behaviour of the isomer. One of the main difficulties that complicated the determination of the structure was that one EO unit in the ethoxylate chain in combination with an additional methylene group in the alkyl chain is equivalent to one PO unit in the ethoxylate chain (cf. table of structural combinations). The overview spectrum of the blend was complex because of this variation in homologues and isomers. The product ion spectrum was also complex, because product ions obtained by FIA from isomers with different EO/PO sequences could be observed complicating the spectrum. The statistical variations of the EO and PO units in the ethoxylate chain of the parent ions of isomers with m/z 568 under CID... 

Ethoxylated sorbitan ester surfactant mixtures like Tween 20 (cf. Fig. 2.9.38) were often used in biochemical applications. Detergents of this type were analysed by MALDI MS. The aim was to compare the separation results of TLC and RP-LC and to detect impurities within these ethoxylated sorbitan esters [30], Tween 20, the ethoxylated sorbitan carboxylate was ionised resulting in [M + Na]+ and [M + K]+ ions. The Tween 20 isomeric and homologue molecules contained a varying number of ethoxylate units. The number of EO units (-CH2CH2O-) was determined from 18 to 34 resulting in Am/z 44 equally spaced signals [30]. 

A typical application of GC to the determination of a drug in plasma is in the determination of the anti-epileptic drug valproic acid after solid phase extraction (see Ch. 15) by GC with flame ionisation detection. In this procedure, caprylic acid, which is isomeric with valproic acid, was used as an internal standard. The limit of detection for the drug was 1 pg/ml of plasma. The trace shown in Figure 11.25 indicates the more extensive interference from background peaks extracted from the biological matrix which occurs in bioanalysis compared to the quality control of bulk materials. 

Several naphthynes have already been investigated in the early 1970s. Griitzma-cher and Lohmann ° generated some derivatives by pyrolysis of different precursors and measured the ionisation potentials of the pyrolysis products. At about the same time, Lohmann investigated the photochemistry of the isomeric naphthalenedicar-boxylic anhydrides 61 and 62 using LFP and found that dimerization of the 2,3-naphthyne (57) is significantly faster than that of 4. The 1,2-isomer 50, on the other hand, hardly dimerizes at all. 

Ionisation Metamerism.—Numerous examples of this type of isomerism occur in the cobalt-ammine series, such as the two metameric substances, ehloro-nitrito-tetrammino-cobaltic chloride, [Co(NH3)4Cl. NOJC1, and dichloro-tetrammino-cobaltic nitrite, [Co(NH3)4C12]N02.1... 

Ammino-derivatives op Cobalt Salts—Cobaltous Salt Ammines—Cobaltic Salt Ammines—Mononuclear Cobalt-ammines containing One Atom of Cobalt in the Molecule—Cobaltic Salts with Trivalent Cation—Cobalt-ammines Containing Divalent Cation—Cobalt-ammines containing Monovalent Cation—Cobalt-ammines consisting of Non-dissociable Complex— Cobalt-ammines containing Monovalent Anion—Cobalt Salts containing Trivalent Anion—Polynuclear Cobalt-ammines containing Two or more Cobalt Atoms in the Molecule—Cobalt-ammines of Unknown Constitution— Ionisation Metamerism—Polymerisation Isomerism—Valency Isomerism —Co-ordination Position Isomerism—Isomerism due to Asymmetric Cobalt Atoms. 

An interesting form of isomerism, dependent on the formation of such cations, is exhibited by chromic salts, which usually exist in at least two modifications, the one green and the other violet or dark blue. In both varieties the chromium is in the same state of oxidation, but the non-metallic radicle, while apparently freely ionised in a violet solution, is only partly active in the green. Thus the chlorine in violet chromic chloride, CrQj.eHjO, is completely precipitated by the addition of a soluble silver salt, but in the ordinary green variety only one-third of See Vol. X. of this series. 

Chromium Chlorsulphates may be prepared either by the action of sulphuric acid on chromic chloride, or by the interaction of hydrochloric acid -with chromium sulphate. Isomeric modifications of these salts exist, for it has been shown that in certain cases the — SO4, and in others the —Cl, is ionised. 

Warfarin is an interesting compound in that, in addition to ionising, it exhibits keto-enol tautomerism. This means that warfarin exists in two constitutional isomeric forms (tautomers) that are in equilibrium with each other, although one of the forms is usually present to a much higher degree than the other. See Figure 3.8. 

Ionisation Hydratisomerie Hexaquochromtrichlorid, CrCl3 6H20, besitzt drei Isomere... 

Quantification was based upon the method generally referred to as internal standardisation using, within each isomeric group, one C-labelled isomer as an internal standard. Inevitable differences in chromatographic retention and/or minor differences in ionisation efficiency, mass spectrometric fragmentation and ion masses monitored, lead to differences in sensitivities between the compounds to be determined and the corresponding C-labelled internal standards. These effects were accounted for in the final concentration calculation by the introduction of isomer specific relative sensitivity factors (RSF). Additional details on this procedure are described elsewhere [18,19]. 

The 3-hydroxy group is very acidic for a phenol but this is not the result of orientation - all isomeric hydroxypyridines show pX s of about 2 for ionisation of the hydroxy group. This effect is presumably due to formation of a zwitterionic structure rather than to any mesomerism. In pyridoxal the pX for OH is 4.2 and that for the pyridinium nitrogen 8.7. The pX of imines is normally 6-7 and although pyridoxal Schiff bases are tiibasic the important species near neutrality are the protonated pyridinium zwitterion (XXVI) or its tautomer (XXVII) and these same structures with the pyridinium nitrogen unprotonated. The pX for loss of a proton from the intramolecularly hydrogen-bonded system is ca. 9 so the anion (XXVIII) must also exist to a significant extent. 

Like the other pentahalides, the mixed pentahalides can either be based on a covalent trigonal bipyramid or exist in ionised forms. Isomeric arrangements of the substituents on the trigonal... 

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