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- W2188088958 abstract "Thenature oftheintramolecular hydrogen bondintheenol tautomer of2,4-pentanedione hasbeeninvestigated byhighresolution proton anddeuteron magnetic resonance spectroscopy. Anunusually large deuterium isotope effect onthechemical shift ofthebridge hydrogen hasbeenobserved. Thisunexpected result, together withtheobservation ofapronounced tem- perature dependence forboththeproton anddeuteron resonances, suggests that twostates withdifferent chemical shifts forthebridge hydrogen areinvolved in rapid equilibrium andthattheanomalous deuterium isotope effect hasitsorigin intheeffect ofdeuterium substitution ontheenergy separation between these states. Itisproposed thatthese states correspond tothesymmetrical and asymmetrical structures oftheintramolecular hydrogen bond. Itiswell knownthat2,4-pentanedione (acetylacetone) exists inboththeenol andketotautomers andthattheinterconversion between these species isslow.1 Thenature oftheintramolecular hydrogen bondintheenol tautomer hasre- ceived considerable interest. There islittle question thatthehydrogen bonding isstrong, since the0-H...0 antisymmetric stretching vibration appears near 2700cm-'intheinfrared spectrum2 andtheproton chemical shift ofthebridge hydrogen isfound tobeapproximately 15ppmdownfield fromTMS.1Reeves hasalso noted thatthechemical shift ofthehydroxyl proton isindependent of concentration andthesolvent system provided thesolvent isnottoobasic.1 Thus, theenol tautomer exists primarily astheintramolecular hydrogen-bonded monomer. Inthis work, theeffect ofdeuterium substitution onthechemical shift ofthe bridge hydrogen hasbeeninvestigated. A pronounced deuterium isotope effect hasbeenobserved. InTable1,wehavesummarized theeffect ofdeuterium substitution onthechemical shift between thebridge hydrogen andthemethyl hydrogens oftheenol tautomer inthepureliquid andupondilution incyclo- hexaneandn-butyl ether.Forcomparison, wehavealsoincluded thecorre- sponding isotope effect onthechemical shift between thehydroxyl andmethyl hydrogens inneatmethanol andacetic acid.Whereas theisotope effects ob- served forthelatter twohydrogen-bonded systems arecomparable tothose normally noted between hydrogens bondedtooxygen andcarbon,3 theeffect observed inthecaseofacetylacetone isanorder ofmagnitude larger. Insofar 816" @default.
- W2188088958 created "2016-06-24" @default.
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- W2188088958 date "1970-01-01" @default.
- W2188088958 modified "2023-09-26" @default.
- W2188088958 title "TheAnomalous Deuterium Isotope Effect ontheChemical Shift oftheBridgeHydrogenintheEnolTautomerof 2,4-Pentanedione" @default.
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