General-base-catalyzed Proton Exchange in Glycocyamidiniom Ions: A Comparison of Activation by Protonation and by Alkylation

1975 ◽  
Vol 53 (19) ◽  
pp. 2906-2910 ◽  
Author(s):  
Ross Stewart ◽  
R. Srinivasan
Keyword(s):  
Exchange Rate ◽  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Proton Exchange ◽  
Resonance Spectroscopy ◽  
Methyl Groups ◽  
General Base ◽  
Satisfactory Model ◽  
Conjugate Acid

The rates of exchange of methylene protons in seven glycocyamidinium ions in formate and chloroacetate buffers were measured in D2O by means of proton magnetic resonance spectroscopy. When protonation and methylation of glycocyamidines occur at the same site the methyated products react faster than the protonated products by factors of 1.8–1.9. Replacing ring protons in glycocyamidinium ions by methyl groups causes small increases in the méthylène exchange rate whereas corresponding substitution at the exocyclic nitrogen causes small rate decreases. It is concluded that in this reaction a quaternary ion ZR+ can serve as a satisfactory model for the analogous conjugate acid ZH+.

Echange isotopique hydrogène–deutérium subi par les groupements méthyles de la triméthyl-4,5,6 pyrimidone-2

1981 ◽  
Vol 59 (8) ◽  
pp. 1270-1276 ◽  
Author(s):  
Eric Picquenard ◽  
Pierre Dizabo
Keyword(s):  
Exchange Rate ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Neutral Molecule ◽  
Resonance Spectroscopy ◽  
Methyl Groups ◽  
Exchange Study ◽  
Conjugate Acid

The rate of deuterium exchange of 4 and 6 methyl protons in 4,5,6-trimethyl-2-pyrimidone has been followed in D2O over a range of acidity from pD 0.4 to 7.7 by means of proton magnetic resonance spectroscopy. The maximum of exchange rate represents equimolar proportions of the pyrimidone and its conjugate acid. The maximum is due to the neutral molecule acting as a base and removing a proton from one of the methyl groups of its conjugate acid. The exchange study of methyl protons in 1,4,5,6-tetramethyl-2-pyrimidone corroborates this mechanism.

Trimethylaluminium: Scrambling of methyl groups in the dimer and exchange with trimethylgallium

1969 ◽  
Vol 22 (6) ◽  
pp. 1129 ◽  
Author(s):  
EA Jeffery ◽  
T Mole
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Methyl Groups ◽  
Cage Effect ◽  
Rate Determining Step

Interchange of methyl groups between the bridging and terminal positions of trimethylaluminium dimer and exchange of methyl groups between trimethyl- aluminium and trimethylgallium in cyclopentane have been re-examined, again by means of proton magnetic resonance spectroscopy. Dissociation of the dimer is confirmed as the rate- determining step in both cases, but the rate of dissociation is much greater in toluene than in cyclopentane. The evidence previously put forward for a cage effect limiting the rate of exchange with trimethylgallium in cyclopentane is refuted and a revised mechanism for exchange is suggested.

Conformations, configurations, and proton reactions of colbalt(III) complexes

1967 ◽  
Vol 20 (2) ◽  
pp. 257 ◽  
Author(s):  
DA Buckingham ◽  
L Durham ◽  
AM Sargeson
Keyword(s):  
Amino Acid ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Proton Exchange ◽  
Resonance Spectroscopy ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans

Proton magnetic resonance spectroscopy allows the cis and trans isomers of [CoX2 en2] complexes to be distinguished. Some information has been obtained concerning the rate of chelate conformational interchange for cobalt-ethylenediamine, propylenediamine, N-methylethylenediamine, and malonate rings. For [Co(amino acid)en2]2+ complexes the diastereoisomeric pairs can be differentiated and the relative rates of CH and NH proton exchange have been observed for a variety of chelate rings including cobalt-amino acid, acetylacetonato, ethylenediamine, and malonato.

Hemi-alkoxides from reactions of trimethylaluminium with aldehydes or ketones

1970 ◽  
Vol 23 (4) ◽  
pp. 715 ◽  
Author(s):  
EA Jeffery ◽  
T Mole
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Alkoxy Group ◽  
Resonance Spectroscopy ◽  
Methyl Groups ◽  
Methyl Group ◽  
Hydrocarbon Solvents ◽  
Analogous Compound ◽  
New Compounds

One mole of an aldehyde or ketone reacts stoicheiometrically with one mole of trimethylaluminium dimer at ambient temperature in hydrocarbon solvents to form a "hemi-alkoxide" in which an alkoxy group and a methyl group bridge two aluminium atoms. Benzaldehyde, acetone, acetophenone, benzophenone, and cyclohexanone give p-alkoxy-p-methyl-tetramethyldialuminiums (Me2A1.OR.Me.AlMe2; R = CHPhMe, But, CphMea2 CPh2Me, and 1-methylcyclohexyl, respectively). Such compounds can also be prepared in low yields starting from alcohols, rather than aldehydes or ketones. The analogous compound, NezAl.N=CPhMe.Me.AlMez, is formed by reaction of benzonitrile with one mole of trimethylaluminium dimer in the absence of solvent at 100�. Exchange of methyl groups between bridge and terminal sites in these new compounds has been studied by proton magnetic resonance spectroscopy.

The Catalysis of Proton Exchange in Creatinine by General Acids and General Bases

1975 ◽  
Vol 53 (2) ◽  
pp. 224-231 ◽  
Author(s):  
R. Srinivasan ◽  
Ross Stewart
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Central Peak ◽  
Proton Exchange ◽  
The Other ◽  
Resonance Spectroscopy ◽  
Acidity Function ◽  
Hydroxide Ion ◽  
Factors Affecting

The rate of exchange of methylene protons in creatinine has been followed in D2O by means of proton magnetic resonance spectroscopy over a range of acidity from pD 12.22 to DA –4.24. A plot of the logarithm of the rate against acidity function is in the form of a "W", one wing of which involves reaction of neutral creatinine with hydroxide ion, and the other diprotonated creatinine with water. The central peak represents reaction of protonated creatinine with a molecule of creatinine acting as base. The reaction is subject to catalysis by buffers.The activation of exchange produced by protonating the substrate is designated protonactivatingfactor, p.a.f., and factors affecting its size are discussed in terms of structure.

scholarly journals Imaging intelligence with proton magnetic resonance spectroscopy

Intelligence ◽  
2009 ◽  
Vol 37 (2) ◽  
pp. 192-198 ◽  
Author(s):  
Rex E. Jung ◽  
Charles Gasparovic ◽  
Robert S. Chavez ◽  
Arvind Caprihan ◽  
Ranee Barrow ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy
Sign in / Sign up

Export Citation Format

Share Document