Positional reactivities and mechanisms of deuteration of 1-methylimidazole in pD and -DO regions. Reinvestigation of the kinetics of 2-hydrogen exchange in imidazole

Wong, John L.; Keck, John H.

doi:10.1021/jo00930a015

Cited by 37 publications

(36 citation statements)

References 4 publications

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“…The rate constant kt corresponding to deprotonation of the neutral substrate is usually derived by plotting data in the high pH region (see eq. [5]) but this could not be evaluated in the present study as noted above.…”

Section: Kinetic Analysis and Reaction Mechanismmentioning

confidence: 80%

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Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

Buncel¹,

Joly²,

Jones³

1986

Can. J. Chem.

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. Can. J. Chem. 64, 1240Chem. 64, (1986. The rate-pH profile for detritiation from the C-2 position of 1-methylimidazole has been determined in aqueous solution at 85°C. The profile is consistent with a mechanism involving attack by hydroxide ion on the conjugate acid of the substrate to give an ylid intermediate in the rate-determining step. At higher pH, hydroxide-catalyzed exchange of the neutral species becomes increasingly important. Comparison of the second-order rate constants derived from the rate-pH profiles of imidazole, 1-methylimidazole, benzimidazole, and 1-methylbenzimidazole showed that methyl substitution caused the rate to increase by 2-to 3-fold while benzo annelation increased the rate by 10-to 20-fold. Frontier molecular orbital (FMO) analysis of the reaction scheme for proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives has been used to explain the rate-accelerating effect of methyl substitution and benzo annelation in these processes.ERWIN BUNCEL, HELEN A. JOLY et JOHN R. JONES. Can. J. Chem. 64, 1240Chem. 64, (1986.Opkrant a 85°C et dans une solution aqueuse, on a determink un profil de la vitesse/pH pour la rkaction de dCtritiation de la position C-2 du mkthyl-1 imidazole. Le profil est en accord avec un mecanisme impliquant une ttape dkterminante dans laquelle un ion hydroxyde attaque l'acide conjuguk du substrat pour conduire a un ylide intermediaire. A des pH plus ClevCs, 1'6change catalysC par des bases des espkces neutres devient de plus en plus important. Une cornparaison des constantes de vitesse du deuxikme ordre, obtenues ? I partir des profils de vitesse/pH, des imidazole, mkthyl-1 imidazole, benzimidazole et mCthyl-1 benzimidazole a perrnis de montrer que la substitution par des groupements mkthyles multiplie la vitesse par 2 h 3 alors que l'annelation par un noyau benzknique multiplie les vitesses par 10 a 20. Dans le but d'expliquer I'acckltration de la vitesse lors de substitutions par des groupements mtthyles et lors de l'annelation par des cycles benzkniques, on a utilisk une analyse, par les orbitales molkculaires frontihres, du schkma rkactionnel des transferts protoniques de l'imidazole, du benzimidazole et de leurs derives substitues par un groupement rnethyle en position 1.[Traduit par la revue]The rate of hydrogen isotope exchange from the C-2 position of the imidazole ring is of interest, in part because of its presence in biologically important systems such as adenine and guanine, fundamental components of nucleic acids, and in drugs such as purornycin. Imidazole is also the primary component of histidine which is present at the active site of many enzymes. The importance of the imidazole ring can be coupled with the use of deuterium and tritium labels as probes in the investigation of chemical and biochemical processes. For instance, the rate of hydrogen isotope exchange from the C-2 position of the imidazole nucleus present in the histidine residues of the enzymes p-lactamase I1 and superoxide dismutase has been used to identify the s...

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Section: Kinetic Analysis and Reaction Mechanismmentioning

confidence: 80%

“…1 Equation [9] is obtained from [5] assuming that the contribution from the hydroxide-catalyzed exchange of the neutral species is small and that the second term can hence be neglected. The agreement with the experimental data is satisfactory.…”

Section: Kinetic Analysis and Reaction Mechanismmentioning

confidence: 99%

Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

Buncel¹,

Joly²,

Jones³

1986

Can. J. Chem.

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“…Imidazoles are much less prone to isotope exchange than their corresponding imidazolium salts. [35,36] …”

Section: Synthesis Of Nmi-dmentioning

confidence: 99%

Characterization of nonderivatized plant cell walls using high‐resolution solution‐state NMR spectroscopy

Yelle

Ralph

Frihart

2008

Magnetic Reson in Chemistry

164

179

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A recently described plant cell wall dissolution system has been modified to use perdeuterated solvents to allow direct in-NMR-tube dissolution and high-resolution solution-state NMR of the whole cell wall without derivatization. Finely ground cell wall material dissolves in a solvent system containing dimethylsulfoxide-d 6 and 1-methylimidazole-d 6 in a ratio of 4 : 1 (v/v), keeping wood component structures mainly intact in their near-native state. Two-dimensional NMR experiments, using gradient-HSQC (heteronuclear single quantum coherence) 1-bond 13 C-1 H correlation spectroscopy, on nonderivatized cell wall material from a representative gymnosperm Pinus taeda (loblolly pine), an angiosperm Populus tremuloides (quaking aspen), and a herbaceous plant Hibiscus cannabinus (kenaf) demonstrate the efficacy of the system. We describe a method to synthesize 1-methylimidazole-d 6 with a high degree of perdeuteration, thus allowing cell wall dissolution and NMR characterization of nonderivatized plant cell wall structures.

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“…Hydrogen-deuterium exchange is well known for imidazole and imidazolium species, occurring at H2 and H4/5 positions on the ring [66][67][68][69]. Despite its common occurrence there have been only a few H/D exchange studies involving azolium cyclophanes, all of them involving imidazolium systems.…”

Section: H/d Exchangementioning

confidence: 99%

Azolium Cyclophanes

Baker¹,

Brown

2006

MROC

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Positional reactivities and mechanisms of deuteration of 1-methylimidazole in pD and -DO regions. Reinvestigation of the kinetics of 2-hydrogen exchange in imidazole

Abstract: Volz and W. D. Mayer, ibid., 4249 (1966). (6) Attempts to prepare 1-halocyclopropyl and -cyclobutyl cations were so far unsuccessful. Further efforts to generate these ions are underway. (7) (a) G. A. Olah and P. E.

Cited by 37 publications

References 4 publications

Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

Characterization of nonderivatized plant cell walls using high‐resolution solution‐state NMR spectroscopy

Azolium Cyclophanes

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