Proton spectral analysis

Mass spectral analysis of quaternary ammonium compounds can be achieved by fast-atom bombardment (fab) ms (189,190). This technique rehes on bombarding a solution of the molecule, usually in glycerol [56-81-5] or y -nitroben2yl alcohol [619-25-0], with argon and detecting the parent cation plus a proton (MH ). A more recent technique has been reported (191), in which information on the stmcture of the quaternary compounds is obtained indirectly through cluster-ion formation detected via Hquid secondary ion mass spectrometry (Isims) experiments. 

Proton magnetic resonance spectral analysis indicates complete conversion to the acid chloride. This may be monitored by following the disappearance of the triplet (C/72C02H) at 6 2.40 and the emergence of a new triplet (C/f2C0Cl) at <5 2.87. 

The H-NMR spectra of compound 71a in DMSO-de showed the presence of a signal at 12.5 ppm corresponding to the exchangeable NH proton, the ethylenic proton as a singlet at S 5.6 ppm, and the aromatic protons appear between 7.27 and 7.80 ppm. The elemental and spectral analysis was in agreement with the structures of these compounds. 

Corsaro and co-workers studied the reaction of pyridazine, pyrimidine, and pyrazine with benzonitrile oxide and utilized H NMR spectral analysis to determine the exact structure of all the cyclized products obtained from these reactions <1996T6421>, the results of which are outlined in Table 1. The structure of the bis-adduct product 21 of reaction of pyridazine with benzonitrile oxide was determined from the chemical shifts of the 4- and 5-isoxazolinic protons at 3.76 and 4.78 ppm and coupled with the azomethine H at 6.85 ppm and with the 5-oxadiazolinic H at 5.07 ppm, respectively. They determined that the bis-adduct possessed /(-stereochemistry as a result of the large vicinal coupling constant (9.1 Hz). Similarly, the relative stereochemistry of the bis-adducts of the pyrimidine products 22-25 and pyrazine products 26, 27 was determined from the vicinal coupling constants. 

One of the major problems has been to determine the site of attachment of the PAH to the base. Some information may be obtained directly from the nmr spectra eliminating certain points of attachment. As mentioned above, if the C-8 proton of guanine or adenine can be identified, then this cannot be the point of attachment of the carcinogen. Estimation of the pKa s of the adducts either by titration (108) or partition (110) has, however, provided additional valuable information. Mass spectral fragmentation patterns can be of help in determining the site of substitution as well as in determining which bases are involved in binding (108.111-113). Substantial advances have been made in recent years on the mass spectral analysis of involatile compounds and derivatization is not always essential (114-118). X-ray analysis of DNA adducts has, to date, only been applied to model systems (119-121). 

The 1H NMR spectrum of the four central protons of 48h was analyzed as an AA BB spin system. The coupling constants between II7/II7 and the deuterium nuclei on C6/C6 (ca 2 Hz) were taken into account as first-order perturbations. In all cases coupling constants over four (—0.58 to —0.87 Hz) and five (+0.32 to +0.69 Hz) bonds were also considered in performing the spectral analysis. Chemical shifts and vicinal coupling constants for 48a-f are reported in Table 14. 

The structure was determined by NMR spectral analysis including a variety of two-dimensional NMR techniques. The 500-MHz XH NMR spectrum of 77 taken in CDCI3 (Figure 26) revealed the presence of 5 aromatic protons, 15 olefinic protons, a methoxy (63.65), an allylic methyl (62.14) and a tertiary methyl group (61.33). The 13C NMR spectrum showed signals due to all 34 carbons, which were assigned to 7 quaternary carbons, 23 methines, 1 methylene and 3 methyls by DEPT experiments. The 13C and XH NMR spectral data are summarized in Table 27. 

Spectral analysis shows quite clearly that the various types of atoms are exactly the same on Earth as in the sky, in my own hand or in the hand of Orion. Stars are material objects, in the baryonic sense of the term. All astrophysical objects, apart from a noteworthy fraction of the dark-matter haloes, all stars and gaseous clouds are undoubtedly composed of atoms. However, the relative proportions of these atoms vary from one place to another. The term abundance is traditionally used to describe the quantity of a particular element relative to the quantity of hydrogen. Apart from this purely astronomical definition, the global criterion of metallicity has been defined with a view to chemical differentiation of various media. Astronomers abuse the term metaT by applying it to all elements heavier than helium. They reserve the letter Z for the mass fraction of elements above helium in a given sample, i.e. the percentage of metals by mass contained in 1 g of the matter under consideration. (Note that the same symbol is used for the atomic number, i.e. the number of protons in the nucleus. The context should distinguish which is intended.)... 

Doublets of the anomeric protons may be suitable as entry points for subsequent spectral analysis or may serve as target spins for additional selective experiments... 

The submitters found that analysis of the final product by gas chromatography indicated a 15% contaminant of the by-product, cyclohexenylacetaldehyde. The analysis was conducted on a column packed with 5% XE-60 on Chromosorb W at 120°. The retention times for cyclohexenylacetaldehyde and cyclohexylideneacetaldehyde were 1.3 and 3.3 minutes, respectively. The checkers found that the product contained 10-15% of cyclohexenylacetaldehyde by gas chromatographic analysis and 12-16% by n.m.r. spectral analysis (deuteriochloro-form solution, tetramethylsilane reference), using the relative intensity of two signals (8 9.53 and 9.97) due to the aldehydic protons of the two compounds. Reported physical constants are b.p. 58-62° (16 mm.) for cyclohexenylacetaldehyde and b.p. 80-85° (16 mm.) for cyclohexylideneacetaldehyde.4... 

Figure 5.10. Sample spectra retrieval from SDBS. (a) 13C-NMR spectrum in DMSO-d6. (b) -NMR (400 MHz) spectrum in DMSO-d6. (c) Mass spectrum, (d) Infrared spectrum in KBr. Sample spectra (including spectral analysis) of uracil are retrieved from Spectral Database Systems. The structure of uracil (molecular weight = 112) is represented with the number corresponding to the position of carbons and the alphabet denoting the position of protons to facilitate NMR assignments ...

The direct attack of proton from the solvent on the intermediate dihydropyridine as well as the over-all mechanism of the reduction received support from the extent and position of deuterium labeling in the product from the reduction of l-methyl-4-phenyl-pyridinium iodide (7) with sodium borohydride in dimethylformamide and deuterium oxide. The l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (9) formed was shown by nuclear magnetic resonance (NMR) and mass spectral analysis to contain approximately one deuterium atom located at the 3-position.13,14 This is the result to be expected from the pathway shown in Eq. (3) if the electrophile were a deuteron. 

The proton magnetic resonance assignments for 241D have been presented (87). The optical rotation, is -1-39° (0.2, CHjOH). The structure of 241D has been confirmed by synthesis (M. W. Edwards, personal communication, 1990). None of the other amphibian piperidines has been isolated for further spectral analysis. However, Bohlmann bands in FTIR spectra will allow assignment of cis or trans configurations to such 2,6-disubstituted piperidines (see Section III,B). 

Deuterium labelling combined with deuterium decoupling is well known as a method in spectral analysis and in stereochemical and conformational studies. The deuterium-decoupled proton spectra of XCHD.CHDY compounds produced during mechanistic studies are useful for determining the stereochemical course of reactions such as the methoxymercuration of ethylene, (478) the conversion of tyramine into tyrosol, (479) the non-catalytic addition of deuterium molecules to cyclopentadiene, (480) and alkyl transfer and olefin elimination in 2-phenyl-l,2-dideuterioethyl transition metal compounds. (481) The proton spectra of [ H ]- and [ Hg]-t-butylcyclohexanes were... 

The proton and nitrogen NMR and UV spectral data for (8) are given in Tables 1, 3 and 4 and a mass spectral analysis of (9) and (10) has been reported in the literature (74CS(6)222). The triazole proton NMR spectral peaks for (11) and (12) are given in Table 5 and the melting points for this series of compounds are presented in Table 6. 

Conversely, the presumed heterolytic C-N bond separation should involve a prior protonation step since this reaction takes place only under strong acid catalysis when it is run at room temperature. In the absence of acid, however, the same process may be thermally induced. There are two potential sites for proton attachment The aziridine nitrogen and the carbonyl oxygen. Both—as protonated species—are suitable to initiate fragmentation of the three-membered ring by way of intermediates VII and VIII, respectively (see Scheme 14.2). While evidence supporting the existence of VIII is available from proton nmr spectral analysis of a V-acrylaziridine in superacid media, other researchers ... 

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