Amino structure

N-Methyl-2-acetamidothiazole is representative of the 2-aminothiazole structure, absorbing at 1542 and 1648 cm its isomeric imino counterpart, 2-acetylimino-3-methyl-4-thiazoline (16), has only one band at 1588 cm . As all acetylated 2-aminothiazoles absorb at 1535 and 1650 cm their amino structure is clearly established (105. 121). 

Experimental evidence (523, 524) agrees with the trend suggested by HMO treatment (see the introduction to Part 2 of this volume), which predicts the preference of the amino structure. 

Pteridin-7-one, 8-/3-D-ribofuranosyl-structure, 3, 282 Pteridinones alkylation, 3, 297 cyanoethylation, 3, 305 structure, 3, 271-273 Pteridinones, amino-structure, 3, 273-276 Pteridin-2-ones... 

Pterin, 4-amino — see Folic acid, 4-amino-4-deoxy-Pterin, 6-amino-structure, 3, 276 Pterin, 7-amino-structure, 3, 276 Pterin, 6-arylthio-reactivity, 3, 299 Pterin, 6-(l-carboxyethoxy)-synthesis, 3, 309 Pterin, 6-carboxy-7-hydroxy-properties, 3, 277 Pterin, 7-carboxy-6-hydroxy-properties, 3, 277 Pterin, 6-chloro-nucleophilic substitution, 3, 292 synthesis, 3, 290... 

Earlier studies of 4-aminopyridine 1-oxide were less conclusive. The solid-state infrared spectrum could be interpreted to indicate the existence of both the imino structure and/or, more probably, the amino structure. Comparison of the actual pKa value of 4-aminopyridine 1-oxide wdth the value calculated using the Hammett equation was considered to indicate that the compound existed as such or as an equilibrium mixture with l-hydroxypyrid-4-onimine, the latter possibility being considered the less likely on the basis of resonance and bond energies/ Resonance energy and ultraviolet spectral considerations have been advanced to support the 4-aminopyridine 1-oxide structure/ The presence of an infrared absorption band at... 

The ultraviolet spectrum of 4-aminoquinazoline has been interpreted to support the amino structure. ... 

Amino-pyrazines and -pyridazines have been shown to exist predominantly in the amino form by infrared spectroscopic studies (cf. Table VI). Ultraviolet spectral data have been interpreted to indicate that 4-aminocinnoline exists predominantly in the imino form 256, but this conclusion, which was based on comparison of its spectrum with those of cinnolin-4-one and 4-ethoxycinnoline, is probably incorrect. Ultraviolet spectroscopic data strongly support the predominance of amino structures for 2-aminopyrazine (257) and 2-aminoquin-oxaline how ever, the former compound was at first erroneously concluded to exist in the imino form from ultraviolet spectral evidence. Isolation of two isomers of 2-amino-8-dimethylamino-3-methylphenazine, assigned the amino and imino structures 258 and 259, respectively, has been claimed, but it is very unlikely that these assignments are correct. 

Likewise for 4-aminopyrazoles 46 and 5-aminopyrazoles 47 (Scheme 28), the most stable tautomer possesses either the amino structure 46a [76AHC(S1), pp. 425, 445 98H(49)157]-or 47a [76AHC(S1), pp. 420, 444 84CHEC-I(5)167 96CHEC-II(3)1], X-Ray structural analysis revealed that the parent 4-aminopyrazole exists in the solid state in two polymorphic forms of amino tautomer 46a these forms differ only by the conformation of the NH2 group [98H(49)157j. 

The nonaromatic amino structure 64 was found by X-ray and by UV and H, and NMR studies (93CB103) to exist as such both in the solid and solution. 

An amino group may take any of three possible positions in the five-membered isoxazole ring, giving rise to three tautomeric forms for 70 and 71 and four forms for 72 [76AHC(S1), pp. 416, 444, 445 84CHEC-I(5)1]. However, only amino structures 70a-72a have been detected using IR- or NMR-spectroscopic techniques (Scheme 33). 

The main factors providing for the amino structure of the complexes 357-359 are relatively low acidity of the amino groups in aminoazoles and... 

A detailed study of spectra of compounds 1, 2, and 3 has been published as part of a general study of azolopyridines (84OMR209). The shifts are shown in Table III. The N shifts have been used to determine the structure of 7-amino-triazolopyridines 128 and 129 (89T7041). The shifts recorded were 56.8, 56.2 (Nl), 245.4, 246.3 (N2), 320.6, 316.8 (N7a), all from nitromethane as standard at 380 ppm the absorption for the amine was at 345.5, 350 ppm in accordance with the amino structure shown, rather than the imino forms 128a and 129a. 

The amino structure 173 was suggested for 5-aminoisoxazoles rather than the imino structure 174 on the basis of tentative chemical data and evidence from the exaltation of the molecular refractivity however, forms of type 175 were not taken into consideration in these... 

The predominance of the amino structure has been demonstrated for 176 (R = Ph, CIl2Ph) by ultraviolet spectral comparisons with both types of alkylated derivatives.Similarly, comparison of the ultraviolet spectra of 2-ainino-5-chlorobenzoxazole (177) and its... 

The opposite conclusion has been reached for similar compounds,but the evidence offered is not convincing. Although definite e-vddence is not yet available, the present authors feel that simple aminopyrazoles probably exist largely in the amino form (cf. 183). More complex aminopyrazoles have been assigned the amino structure by Taylor and Hartke on the basis of chemical, infrared, and ultraviolet spectral data. 

Dimethylamino)-4-oxo-5-phenyi-seienazoline, synthesis, amino structure, 262... 

The amino structure for 9-aminoacridine (77) has been confirmed by IR studies (65JCS5230), and NMR spectral data in DMSO are consistent with the diamino structures (78) and (79) (64JCS1423). Amino groups on fused benzene rings and (3 to nitrogen in hetero rings exist in the amino form, and the reactions of these compounds are similar to those of aniline and the naphthylamines. Aminopyridine JV-oxides exist very predominantly in the amino form (57JCS4375). 

Barton (Ref 2) showed that this isomer is formed when an alkaline solution of the preceding entry is allowed to stand a day or so. Apparently there is no literature mention of its actual isolation, although the earlier Refs for the preceding entry use the (a)amino structure Refs l)Beil, not found 2)S.S.Barton, et al, JACS 73, 2201-5(1951) CA46, 1988 (1952)... 

Aminopyrazolopyrimidines exist in the amino form. The only exception is 7-aminopyrazolo[l,5-a]pyrimidine, which exists in the solid state as an amino-imine mixture. The evidence is not conclusive (70BCJ849). Previous work on the same series has assigned an amino structure (62CPB620). Other aminopyrazolo[l,5-a]pyrimidines investigated were shown to exist in the amino form (74JHC423). 

Pterin-4-one, 2-amino-structure, 3, 273 Pterin-7-one, 2,4-dimethoxy-hydrolysis, 3, 299 Pterin-6-ones reactions... 

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