Tautomerism intramolecular

The list of publications in the obituary of the organic chemist Otto Dimroth (1872-1940)139 has eleven papers that are classified as physikalisch-organische Chemie. They are mainly about tautomerism, intramolecular rearrangements, and solvent effects on tautomeric equilibria. One paper,140 published in 1933, deals with relationships between reaction velocities and oxidation-reduction potentials for quinone systems and it is evident that Dimroth was a pioneer in developing linear free-energy relationships. He was Professor in Wurzburg from 1918 to 1940. 

Figure 8-4. Schematic picture of tautomeric intramolecular proton transfer in malonaldehyde...

Chapter 8 (Perimidinespirocyclohexadienones). This series constitutes a rather new photochromic or thermochromic system based on proton transfer involving valence and prototropic tautomeric intramolecular reactions (Scheme 8). 

Shchavlev, A.E., Pankratov, A.N., and Shalabay, A.V., DFT computational studies on rotation barriers, tautomerism, intramolecular hydrogen bond and solvent effects in 8-hydroxyquinoline, Int. J. Quantum Chem., 106, 876-886 (2006). 

Another type of tautomerism, intramolecular in nature, is called valence tautomerism (or valence isomerization). Valence tautomers rapidly interconvert with one another, but the tautomeric forms differ principally by the positions of covalent bonds, rather than by the positions of protons. 

Another type of tautomerism, intramolecular in nature, is called valence tautomerism (or valence isomerization). Valence tautomers rapidly interconvert with one another, but the tautomeric forms differ principally by the positions of covalent bonds rather than by the positions of protons. There are many examples of valence tautomerism in the literature. An interesting example is the isomerization of bullvalene, an interesting compound with threefold symmetry. At low temperatures (below -85°C), the proton NMR spectrum of bullvalene consists of four complex multiplets (each... 

Tautomerism has been discussed in Section 4.04.1.5.2. It concerns prototropic tautomerism and the decreasing order of stability is (hydrazone) >A (azo)> A (enehydrazine). The isomerization A -> A occurs via a A -pyrazoline (65BSF769). Pyrazolidones and amino-A -pyrazolines exist as such. The only example of non-prototropic tautomerism deals with the isomerization (403) —> (404) (74CJC3474). This intramolecular process is another example (Section 4.04.1.5) of the thermodynamic analogy between prototropy and metallotropy. 

C NMR, 6, 398 molecular dimensions, 6, 397 tautomerism, 6, 404 Furoxan-3-carbohydra2ide intramolecular hydrogen bonding, 6, 396 Furoxan-3-carboxamide intramolecular hydrogen bonding, 6, 396 Furoxancarboxylic acids reactions, 6, 413 with nucleophiles, 6, 406 Furoxan-3,4-dicarbaldoxime synthesis, 6, 409 Furoxanoaaines fused... 

DFT STUDY OF 8-MERCAPTOQUINOLINE INTRAMOLECULAR HYDROGEN BOND, SINGLE PROTON TRANSFER AND WATER-ASSISTED TAUTOMERIZATION... 

The above value for R = H corresponds to an intermolecular process, either assisted by the solvent (in solution) or by other NH-pyrazole molecules (in solution and in the solid state) while metal migrations are probably intramolecular (the bigger the metal, the easier) and those of COR correspond (for R = NHR ) to a dissociation-recombination mechanism. Minkin [quoted in 96MI(15)339] suggests that a tautomeric process should... 

Numerous data on kinetics of annular tautomerism have been obtaifled for the degenerate rearrangements of pyrazole derivatives. Since all these rearrangements were found to be intramolecular, we can compare kinetic measurements carried out in different media. The following order of increase in migration ability of various groups is established ... 

The amino form 66a of 5-pyridylamino-l,2,4-triazole stabilized by two intramolecular hydrogen bonds is the only tautomer observed by the X-ray study of the crystal (90KGS1632). However in DMSO-dg, DMF-d7, and HMPA-di8 solutions, the equilibrium involves three tautomeric forms 66a-66c (Scheme 31) (90KGS1632). 

Tliere are several reasons for this great interest in the tautomerism of porphyrins (which could justify its own review) (1) their biological significance, (2) their applications in material science ( hole burning is related to their tautomerism), (3) the simplicity of the system (annular tautomerism involving intramolecular proton transfer both in solution and in the solid state), and (4) the possibility of elucidating the kinetic processes in great detail. 

Such modifications can be produced either in the kinetic aspects (proton transfer) or in the equilibrium constant. Both effects are mediated by intramolecular hydrogen bonds. For instance, Navarro et al. (93MI69) showed that the rate of proton transfer between the two nitrogen atoms of pyrazole (annular tautomerism) is considerably reduced in macrocycles containing oxygen or nitrogen atoms in the macroring. 

Ring-chain tautomerism via intramolecular reversible addition reactions to the C=0 group 95AHC(64)251. 

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