Thiones structure

Although 1,2,4-triazinethiones have usually been formulated in the mercapto form, e.g. 221 (cf. reference 273), infrared and ultraviolet spectra appear to support the thione structure 222. However, on the basis of its infrared spectrum, 223 exists in the mercapto form,... 

Mercaptopurine probably exists in a thione form (e.g., 167) since its ultraviolet spectrum is different from that of 2-(methylthio)pur-ine. Purine-2-thione and its 6-amino derivative were assigned thione structures on the basis of their infrared spectra.8-Mercapto-9-methyl- and b-mercapto-T-methjd-purine exist at least partially in thione forms, presumably 168 and 169, respectively, since their in-... 

Methylselenophene-2-thiol and 2,5-dimethylselenophene-3-thiol have been shown to exist as thiols by NMR and IR spectroscopy as well as by comparison of gas phase ionization potentials with those of appropriate model compounds (77ACS(B)198). Dipole moment studies have supported formulation of selenophene-2- and -3-thiols as such (73BSF1924) rather than the 2-thione structure originally proposed for the former compound (71BSF3547). 

The structure of the parent acid of salts obtainable from reaction of azides and carbon disulfide and still often called azidodithio-formates or -carbonates.The isolable acid has an isomeric thione structure. 

In the case of 5-thio derivatives, the IR spectra show no clear SH absorption as would be anticipated for (17a), and the thione structure (17b) or (17c) was tentatively assigned (Scheme 10) (73CJC2353). The IR spectrum in Nujol of perthiocyanic acid is considered to indicate that the dithione structure (18a) is favored over (18b) (63JCS3168). 

This satisfactory method was also used to settle the similar thione-thiol (15-16) problem of 5-mercaptothiatriazole which was claimed by Jensen and Pedersen to exist in the thiol form (64AHC(3)263). However, in the 13C NMR spectrum of 5-mercaptothiatriazole (0°C, acetone-[Pg.583]

An NMR study of stereoelectronic effects in dithiolane sulfoxides such as 35 has appeared <07CEJ4273> and the new donor-acceptor system 36 has been examined for possible use in solar cells. A variety of new crystallographic studies of l,3-dithiole-2-thione structures have... 

Potential 2-hydroxy- and 2-mercapto-l,3,4-thiadiazoles have been examined both by infrared and by ultraviolet spectra in the solid state and in solution by Sheinker et They concluded that these compounds exist in the 2-oxo and 2-thione forms, respectively. To 2,5-dimercapto-l,3,4-thiadiazole the 2-mercapto-5-thione structure (155) was given. The structure of this compound has been the subject of some controversy. Stanovnik and TiSler have added some valuable arguments to the discussion. They measured the pKfl values of 155, its iV-methyl, iV -phenyl, and iV -phenyl-/S-methyl derivatives (156), and of the conjugate acids of these and the S-methyl derivative (pKn ) (Table III). In all compounds 156 with R = H, the infrared spectrum showed an absorption band near 2300 cm characteristic of the SH group. They also had pK i values near —1.5, Avhich in connection with the infrared evidence was taken as characteristic of an SH group in this situation. Since the 2,5-dithiol structure is excluded by ultraviolet spectral evidence, the 2-mercapto-5-thione structure (155) seems rather well established. It has previously been shown bj Thorn to predominate in chloroform solution, whereas he concluded that the dithione form (157) should predominate in ethanol solution. However, the pK i value for 155, — 1.36, makes it rather probable that Thorn used the monoanion of 155 instead of the acid itself for spectral comparison, and in that case his conclusions have a very weak foundation. 

The best known of the potential mercaptoimidazoles are the imidazoline-2- and benz-imidazoline-2-thiones, which resemble imidazolin-2-ones in that the tautomeric form (53 X = S) is the preferred form. The crystal structure and the HNMR spectrum of 1,3-dimethyl-3H-imidazoline-2-thione have been interpreted as showing partial double bond character in the N—C—N system, but no aromaticity (70CC56). However, the preference for a betaine structure (56) rather than (57) or (58) should be accepted with caution since it is really only a resonance structure similar to others which undoubtedly contribute to the overall structures of oxo-, thio- and amino-imidazoles. Measurement of the piSTa values for a series of imidazoline-2-thiones substituted variously on C-4, C-5, N-1 and N-3 by hydrogen, phenyl or methyl shows that all of the values are similar. Approximate Kr values calculated show that these compounds exist even more in the thione forms (53, X = S 58) than do the corresponding thiazoline-2-thiones and oxazoline-2-thiones. The UV spectra in aqueous solution support thione structures, as do dipole moment and X-ray studies (76AHC(S1)280, p. 400). 

Imidazolidine-2-thiones (or 2-ones) have been shown by NMR studies to exist entirely in these forms rather than as the possible 2-mercapto-(or 2-hydroxy-)2-imidazoIines (80CS(15)193). The thione structure for benzimidazolinethiones is supported by UV, IR and dipole moment measurements. In addition, an X-ray study of l-(j8-D-ribofuranosyl)benz-imidazoline-2-thione confirms its thione (59) rather than the thiol (60) structure (Scheme 19). 

In contrast to the 2,4-dioxoimidazoles (and such compounds as 5-phenyl-2-thiohydan-toin), there is convincing evidence (UV, IR, NMR data) that imidazolidine-2,4-dithiones exist mainly in the thione-thiol forms (84 Scheme 27). The two tautomers (85,86) have been separated in 5,5-diphenylimidazoIidine-2,4-dithione in KBr the C=N bands appear at 1495 and 1575 cm , respectively. In the 5,5-spiropentane analogues the structure related to (85) increases in importance as the solvent polarity increases. As mentioned above, the oxo-thione structures for imidazolin-4-one-thiones is supported by IR spectra in the solid state, and by UV spectra in ethanol. The partially fixed derivatives (87,88 Scheme 28) can be crystallized separately, but give identical spectra in solution. Both X-ray crystal structures and solid state IR spectra confirm the existence of two structures (87 y(C=0) 1690, r(C=N) 1510-1490 cm ) and (88 r(C=0) 1720, r(C=N) 1590-1575 cm ). As with the dithiones, the importance of the cross-conjugated form (88) increases with decrease in solvent polarity. 

Hydroxytriazoles and tautomeric triazolinones have a common mesomeric anion, hence their spectra are affected in basic solvents. UV spectra have been used to demonstrate the predominantly dioxo structure of l-phenyl-l,2,4-triazolidine-3,5-dione (66T(S7)213) and the thione structure of mercaptotriazoles (66ACS57) utilized also in theoretical work. 

The reaction of 36 with sulfur in dimethylformamide gave a compound which was originally ascribed the l,2-dithiole-3-thione structure 37.72 X-Ray studies, however, showed that the coronenelike trithiapentalene structure... 

Sato and Ohta (307) who reinvestigated the reaction of dithiocarbazic acids with chloroacetone and w-bromoacetophenone also described the 3.4-dihydro-2H-1,2,4-thiadiazine-2-thione structure to the products. These authors also describe the condensation of N-benzoyl dithiocarbazic acids (CCXV, Rj—CgHjCO with a-halo ketones which yields 4-benzoyl-3,4-dihydro-2H-t, 3,4-thiadiazine-2-thiones (CCXVIII, These products hydrolj ze in acid medium (with formation of benzoic acid) and simultaneously undergo a transformation to 3-amino-zl4-thiazoline-2-thiones. These facts support the remarks made earlier. 

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