Nuclear Magnetic Resonace Research Articles

Nuclear magnetic resonance spectra of pyrido‐ and azapyridocyanines

AbstractThe nuclear magnetic resonace spectra of six pyridocyanines, four azapyridocyanines, one monoquaternized 2,4′‐dipyridylamine and two dipyridylamines were measured and fully analyzed. The spectra of the 2,2′‐pyrido‐ and azapyridocyanines support previously published results that these dyes exist in the all‐trans form and not in the mono‐cis form, as stated by others. Strong evidence was obtained that N,N′‐ethylene‐2,2′‐pyridocyanine is twisted. The spectra of dyes with p‐connected pyridine rings indicate that these nuclei may rotate around the bond between the meso group and the p‐position. Relative chemical shifts in the spectra of the homologous pyrido‐ and azapyridocyanines can be explained by electronic effects rather than by magnetic anisotropy of the aza group or changes in ring currents.

Side chain interactions in aromatic dipeptides

AbstractA study of the 100‐MHZ nuclear magnetic resonace spectra in D2O solution was made of a series of linear dipeptides of the types L‐phenylalanine‐L‐and‐D‐X, and L‐phenylalanine‐L‐and‐D‐Y, where X comprised a group of amino acid residues with polar side chains (X = glutamine, glutamic acid, arginine, and Nε‐acetyllysine) and Y comprised amino acid residues with purely aliphatic side chains (Y = α‐aminobutyric acid and norvaline). It was found that regardless of the side chain length, resonances due to the α‐methylene protons in the X and Y side chains of the L‐Phe‐D‐Y series consistently exhibited upfield shifts greater than any other protons in these side chains, when compared to the corresponding side chain resonances of the nonaromatic dipeptide series L‐Ala‐L‐X and L‐Ala‐L‐Y. The magnitudes of these shielding effects were consistently and considerably greater for the L‐Phe‐D‐X series than for the L‐Phe‐D‐Y series. An intramolecular complex–formed by association of armatic π‐electrons with the positive end of the dipole in the polar side chains—was proposed as one plausible interpretation of the enhanced shielding effects. An increase in temperature from 32 to 70–80° was sufficient to overcome the enhanced shielding attributable to the suggested complex.

Proton and phosphorus-31 nuclear magnetic resonace studies of tetraalkoxyhosphonium hexachloroantimonates and related compounds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProton and phosphorus-31 nuclear magnetic resonace studies of tetraalkoxyhosphonium hexachloroantimonates and related compoundsJack Sidney. CohenCite this: J. Am. Chem. Soc. 1967, 89, 11, 2543–2547Publication Date (Print):May 1, 1967Publication History Published online1 May 2002Published inissue 1 May 1967https://doi.org/10.1021/ja00987a008RIGHTS & PERMISSIONSArticle Views99Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (651 KB) Get e-Alerts Get e-Alerts

Solvent shifts in the nuclear magnetic resonance spectra of unsaturated carbonyl compounds.

Solvent shifts in the nuclear magnetic resonance spectra of unsaturated carbonyl compounds.