Ultraviolet and Infrared Spectra

Ultraviolet and Infrared Spectra.—The effect of conjugation in the excited state of some silicon-substituted thiophens has been discussed. The u.v. and i.r. characteristic absorption spectra of some pairs of cis- and rra/75-isomers of 2 - and 3 -substituted 2-styrylthiophens have been determined. It is claimed that the spectra of the stereoisomers are sufficiently different to assign the configuration. The i.r. and Raman spectra of 4-chloro-, 4-bromo-, 4-iodo-, and 4-cyano-2-fluoro-thiophens have been studied in the region 500—540 cm . The fundamental frequencies have been assigned, and normal co-ordinate calculations have been performed. The force constants were adjusted to reproduce accurately the fundamental frequencies. Thermodynamic functions and mean amplitudes of vibration for these molecules were also calculated. Thiophen-2-aldehyde and 19 related aldehydes have been studied under high resolution in the i.r. C=0 region. 

Sb2(C6F4)3 is a very robust molecule, being stable indefinitely in the open air at ambient temperatures. Near the melting point (258°), some 

This reaction was used originally to demonstrate that tetrafluoro-phenyl groups were present in molecule. 

Perfluorodistibatriptycene is unaffected by cold, concentrated nitric acid but dissolves with oxidation on boiling (ff) dilution of the solution with water results in the deposition of Sb2(C6F4)3(N03)2(0H)2 as needlelike, colorless crystals. This nitrate slowly hydrolyzes on repeated crystallization from water to give Sb2(C6F4)3(OH)4 attempts to dehydrate this tetrahydroxo derivative to the above polymeric oxide have so far failed. The stereochemistry of these Sb(V)-substituted triptycenes would be of great interest but all the crystals yet studied have proved to be twinned. 

Heating together antimony, antimony trioxide, and 1,2-diiodotetra-fluorobenzene in a sealed tube failed to give the antimony analog of the arsenic epoxide (III) because some Sb2(C6F4)3 was formed in this system it is also obvious that the triptycene does not react with Sb203 at 260°. 

The very low solubility of perchlorodistibatriptycene has considerably hindered attempts to explore its chemistry, and virtually the 

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Both carbonyl groups of terephthaldehyde are reported to react with the exocyclic nitrogen of 2-aminothiazole yielding 1.4-phenylene bis(2-methyleneamino)thiazole. The same report describes the reactions of 2-amino-4-phenylthiazole with terephth aldehyde and salicylaldehyde as yielding 64 and 65, respectively (Scheme 45) (215), whose structures are based on ultraviolet and infrared spectra. 

The ultraviolet and infrared spectra and the crystal structure (as determined by X-rays) of cyanuric acid have been interpreted on the basis of the trioxo structure 157 however, other ultraviolet data have been reported from which it was concluded that approximately 5% of this compound exists in a hydroxy form in solu-tion. The monoanion of cyanuric acid exists as 158. Ultraviolet spectral data suggest that ammelide (159) and ammeline (160) exist as shown (available infrared spectra offer less conclusive evi-... 

The anomalous behavior of quinazoline was first discovered by Albert et who made the surprising observation that 4-methyl-quinazoline 2.5) was a weaker base than quinazoline (pA 3.5). Mason then observed that the ultraviolet spectrum of the quinazoline cation was abnormal but that the spectrum of 4-methylquin-azoline was normal (see Fig. 2). These anomalies led to the suggestion that water adds covalently to the cation of quinazoline to give 12 (R = H). The occurrence and position of hydration were confirmed by a detailed study of the ultraviolet and infrared spectra of the anhydrous and hydrated hydrochlorides and by mild oxidation of the cation to 4(3 )-quinazolinone. Using the rapid-reaction technique (the continuous-flow method), the spectrum of the unstable... 

The ultraviolet and infrared spectra of 2-aminothiazole and the methyl derivatives of both the imino and the amino forms have been compared and discussed by Sheinker, Kushkin, and Postovskii ° who showed that the amino form predominates in the solid state and in various solvents. The reaction of 2-aminothiazoles with methyl iodide in the presence or in the absence of sodium ethoxide has been considered to give information concerning the proportion of the amino and imino forms present under these conditions, ... 

Substituted 2-amino-l-thia-3,4-diazoles have been studied by Testa et Comparison of ultraviolet and infrared spectra of the parent compound (197 198) with those of its four possible methylated derivatives indicated that 197 predominates in aqueous solution and... 

This stearolic acid has been thoroughly characterized 3 6 by the freezing-point curve, ultraviolet and infrared spectra, ozonization, and hydrogenation. It has been shown to be free both of positional isomers and of olefinic acids such as oleic and elaidic acids. Its properties include m.p. 46-46.5°, iodine number (Wijs titration, 30 minutes) 89.5, d 5 1.4510, d 5 1.4484, neutral equivalent 279.2-279.6 (theory 280.4), hydrogen uptake 95-100% of theory for a triple bond. The last trace of color is difficult to remove by recrystallization from petroleum ether. It can be removed, however, by crystallization from a 20-30% solution in acetone at —5 to —8°, or from an 8-10% solution at —20°, or by distillation (b.p. 189-190°/2mm.). 

In general more independent physical constants that are sensitive to structure are needed when it is necessary to know more structural elements of a mixture. It will be clear that, dependent on the collected basic data, statistical methods for the analysis of mixtures in general only give a certain approach to their structures, but should never be considered as the ultimate purpose. Improvement of existing methods is imperative when new and more accurate data become available the development of various physical separation methods (distillation, chromatography, thermodiffusion, etc.) and of independent physical identification methods (ultraviolet and infrared spectra, mass spectrometry) may also contribute considerably to their perfection. 

Cagniant, D., Faller, P., and Cagniant, P., Contribution in the study of condensed sulfur heterocycles. XVII. Ultraviolet and infrared spectra of some alkyl derivatives of thianaphthene, Bull. Soc. Chim. Fr., 2410, 1961. 

Existing experimental evidence, particularly from ultraviolet and infrared spectra,186,456 suggests that 2- and 4-hydroxyimidazoles exist predominantly in the azolone form (cf. 96). Since Pozharskii et al.3 and Roger and Neilson457 discussed methods of synthesis of... 

The deposits containing reactive intermediates have been examined by ultraviolet, infrared and e.s.r. spectroscopy. The stable products which are formed when the deposits are warmed have also been analysed by g.l.c. The observations of the ultraviolet and infrared spectra have been carried out in situ with the deposits remaining on the cold drum. In contrast, examinations by e.s.r. and g.l.c. have necessitated the removal of the deposits from the drum and their transfer into sample tubes. Of these methods, e.s.r. has been used most extensively as it is ideally suited to the examination of free radicals. 

The ultraviolet spectra in aqueous solution (821) of the methiodides isolated from the methylation of 2-amino- and 2-dimethylaminopyrazines with methyl iodide in methanol (821) differed from those obtained by protonation of 2-amino-and 2-dimethylaminopyrazine, respectively. This methiodide of 2-aminopyrazine was rapidly decomposed by aqueous alkali but did not form l-methyl-2-oxo(or imino)-l, 2-dihydropyrazine or 2-methylaminopyrazine (821). These and other observations were consistent with protonation of 2-amino(2-methylamino or 2-dimethylamino)pyrazine at N, and with the methiodides isolated involving quater-nization at N4 (821). It has been claimed from studies of ultraviolet and infrared spectra and from reactions with cyanoguanidine that in 2-aminopyrazine p-toluenesulfonate, the amino group is protonated (1189). 

Efforts were made to determine the structure of the oxygenated dibenzenechromium. Based on analysis, ultraviolet and infrared spectra, the following composition was assigned to the catalyst ... 

Ultraviolet and infrared spectra have been considered in some detail in the section dealing with structure. Concerning the ultraviolet spectra it can be stated that, while there is considerable absorption by pryazolinones and some pyrazolidinones, these absorptions are so complex, owing to tautomerism, that little can be deduced from them. 

The ultraviolet and infrared spectra of heteroaromatic systems are in accord with their aromatic character. Spectroscopic investigation, particularly ultraviolet/visible (UVA IS) and nuclear magnetic resonance (NMR) spectroscopies, is particularly useful in the context of assessing the extent of such properties, in determining the position of tautomeric equilibria, and in testing for the existence of non-isolable intermediates. 

This mechanism is supported by the fact that a bright yellow substance can be isolated from the products of complete alkaline hydrolysis of irradiated polycarbonate, the ultraviolet and infrared spectra of which are very similar to those of 2,2 -dihydroxybenzophenone (see Figs. 22 and 23). This substance is most probably the dimer, with a structure similar to... 

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