Pyrroles, spectral data

Tables of experimental data for monosubstituted (71PMH(3)67, p. 74) and polysubstituted (B-64MI30400) pyrroles are available (see also B-74MI30400) the reader s attention is also directed to the general compilation (by molecular formula) of Organic Electronic Spectral Data .

In contrast with the hydroxy compounds, comparatively little is known of the tautomeric preferences of pyrrole- and indole-thiols. The compounds are readily oxidized to form the bis-heteroaryldisulfides and the available spectral data for the monomeric systems suggest that, in contrast with the oxygen analogues, the 2-pyrrole- and 3-indole-thiols exist predominantly as such, whereas the sulfur analogue of oxindole is the predominant tautomer for the 2-indolyl system <63AHC(2)1,76AHC(SuppI. 1)214). 

The mass spectra of pyrrole, four C-alkyl, and two A-alkyl derivatives are to be found in the American Petroleum Institute catalog of mass spectral data.318 Other publications report the most abundant fragment peaks of some N- and C-substituted pyrroles.313,314... 

In spite of the proliferation of isolated UV spectral data for individual pyrroles, relatively few attempts have been made toward a systematic study of the effects of substituents upon the positions and intensities of the absorption bands. The detailed spectra of alkyl,192 409 phenyl410-414 acyl,415-417 formyl,378,418,418a and their oximino419,420 and Schiff s base421 derivatives, cyano,177,378 car-... 

Interpretation of these mass-spectral data in Table IV combined with the titration data from Table III allows additional inference concerning the characteristics of the nitrogen compounds present in the very weak base concentrate. The sum of the compound types listed as pyrroles and indoles (Z =-= —7, —9, —11, and —13) amounts to 29% of the total. These compound types have given (II) very weak base titers of about 70% of theoretical thus it appears likely that the 19.8% titer for very weak bases in Table III may come from the titration of the pyrroles and indoles in this concentrate. In addition, they are not N-substituted... 

The UV spectral data of known parent A,B-diheteropentalenes are summarized in Table 9. The analogous thienothiophenes and selenolothiophenes show more absorption maxima in their UV spectra than the other systems. The known progressive shift of absorption to longer wavelengths which is observed in the simple five-membered heterocycles in the sequence furan < pyrrole < thiophene < selenophene is missing since the rings are fused. 

Table 1 Selected pyrrole and triazole experimental agents and their corresponding mass spectral data. H NMR for experimental materials supplied by author...

Phakellins (41, 42), tetracyclic derivatives in which both the pyrrole and the amidic nitrogen atoms are involved in the formation of a linkage with carbon atoms of the imidazole ring, represented the first members of the family of oroidin-related cyclic bromopyrrole alkaloids to be isolated. They were found in 1971 by Sharma et al. in the marine sponge Phakelliaflabellata their structure was confirmed by X-ray diffraction analysis of a single crystal of the monoacetyl derivative of 41 [70]. Complete spectral data were provided by the same authors a few years later [71]. 

Depending on the reaction conditions, pyrrole amide 45 cyclizes either to pyrrolo[l,2- z]pyrazin-l-ones (46) or to a mixture of pyrrolo[2,3-c]pyridin-7-ones (47) and pyrrolo[3,2-c]pyridin-4-ones (48) [42], Isomers 47 and 48 are distinguishable by the lower chemical shift of the N—H proton (10.21 ppm) for 47 syn to the carbonyl) relative to that observed for 48 (9.08 ppm) and other spectral data. The cyclization leading to 47-48 is proposed to involve spiro intermediate 49. 

LeBerre and Renault have utilized 2-amino-1-pyrroline (30) in condensation reactions with a,/3-unsaturated carbonyl derivatives and -di-carbonyl compounds to prepare a wide variety of partially saturated pyrrolol 1,2-aIpyrimidines in which the pyrrole portion of the molecule is always completely saturated. For example, condensation of the amino-pyrroline (30) with substituted maionic esters (29) affords13,14 2-hydroxy-4,6,7,8-tetrahydropyrrolo[l,2-a]pyrimidin-4-one (31a). Spectral data indicate the betaine form (31b) to be preferred [Eq. (5)]. 

The greater lability toward vanadium removal and porphyrin destruction for the vanadyl petroporphyrins over the synthetic vanadyl porphyrins is a fortunate circumstance. This difference can be rationalized based upon structural differences of the porphyrins involved. Phyllo-type petroporphyrins all contain a cyclopentane ring, fused to one of the pyrrole rings with the methine carbon one of the units of the carbo-cyclic structure. Etio- and rhodo-type petroporphyrins appear to have alkyl substitution at one or more methine positions, as based upon nmr spectral data. Should all petroporphyrins have a carbon substituent on one or more methine carbons, the carbonium ion formed by the reaction would tend to have more charge localization on those methine carbons. These ions are a more stable species by an order of magnitude over those porphyrins without methine substitution. 

In last year s Report, reference was made to the discovery of three examples of a new type of pyrrolizidine alkaloid containing the dihydropyrrolizinone ring system. Two closely related acyl-pyrroles have now been detected in aerial parts of Kleinia kleinioides (Sch. Bip.) M. R. F. Taylor by Bohlmann and Knoll. Spectral data on the first pyrrole showed it to be an isomer of senaetnine (29), with different stereochemistry at C-7, C-12, or C-13. Lack of material prevented clarification of the stereochemistry of isosenaetnine (29). The second new compound differed from isosenaetnine in replacement of one methyl group by methylene, and it is therefore formulated as dehydroisosenaetnine (30). The stereochemistry is again uncertain. 

Ushakov, I.A. 2006. Structural peculiarities of C2-substituted pyrroles according to H, and NMR spectral data. PhD dissertation, Irkutsk State University, Irkutsk, Russia. 

Thus, the data obtained show that chloroform and acetylene and its derivatives are suitable IR-spectroscopic probe-molecules for basic centers in zeolites. These probes exhibit the following advantages as compared to the conventionally used molecules, like CO2 and pyrrole (1) the wride ranges of the frequency shifts, which allows one to differentiate the centers of different nature and strength, (2) the easiness and reversibility of adsorption/desorption of these molecules, and (3) the favorable spectral range where the spectral features attributed to adsorbed probes appear. The use of such an approach allows us to shed some light on the nature and properties of basic sites in zeolites. The similar technique will be applied in our future studies devoted to other solid superbases. 

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