EXCHANGE BROADENING OF SPIN–SPIN TRIPLETS IN NUCLEAR MAGNETIC RESONANCE SPECTRA. APPLICATION TO THE SYSTEM ETHANOL–WATER

1963 ◽  
Vol 41 (3) ◽  
pp. 714-720 ◽  
Author(s):  
W. G. Paterson
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Proton Exchange ◽  
Average Lifetime ◽  
Hydroxyl Proton ◽  
A Value ◽  
Nuclear Magnetic Resonance Spectra ◽  
Spin Triplets ◽  
Exchange Broadening ◽  
Nuclear Magnetic

Using an extension of the method of McConnell (1), an expression is derived for the nuclear magnetic resonance spectrum of a hydroxyl proton in a —CH2OH group which is undergoing intermolecular exchange. A graphical method is presented which enables a rapid evaluation of τ, the average lifetime of a hydroxyl proton between exchange events. Measurements of line widths and multiplet spacings in the n.m.r. spectra of ethanol—water solutions are interpreted in terms of the proton exchange reaction[Formula: see text]for which a value of 2.7 1. mole−1 sec−1 at 42 ± 1 °C is suggested as an upper limit to the rate constant.

Selenium-77 nuclear magnetic resonance studies of selenols, diselenides, and selenenyl sulfides

1988 ◽  
Vol 66 (1) ◽  
pp. 54-60 ◽  
Author(s):  
Khoon-Sin Tan ◽  
Alan P. Arnold ◽  
Dallas L. Rabenstein
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Proton Exchange ◽  
Exchange Reactions ◽  
Nuclear Magnetic Resonance Spectra ◽  
Ph Range ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

77Se and 1H nuclear magnetic resonance spectra have been measured for selenols (RSeH), diselenides (RSeSeR), and selenenyl sulfides (RSeSR′), including selenenyl sulfides formed by reaction of glutathione and penicillamine with selenocystine and related diselenides. Exchange processes strongly affect the 77Se and 1H nuclear magnetic resonance spectra of all three classes of compounds. Sharp, exchange-averaged resonances are observed in the 1H nuclear magnetic resonance spectra of selenols; however, selenol proton exchange causes the 77Se resonances to be extremely broad over the pH range where the selenol group is titrated. Selenol/diselenide exchange [Formula: see text] also results in exchange-averaged 1H resonances for solutions containing RSeH and RSeSeR; however, the 77Se resonances were too broad to detect. Exchange reactions have similar effects on nuclear magnetic resonance spectra of solutions containing selenols and selenenyl sulfides. The results indicate selenol/diselenide exchange is much faster than thiol/disulfide exchange. The 77Se chemical shift depends on the chemical state of the selenium, e.g., titration of the selenol group of selenocysteamine causes the 77Se resonance to be shielded by 164 ppm, oxidation of the selenol to form the diselenide selenocystamine causes a deshielding of 333 ppm, and oxidation to form the selenenyl sulfide [Formula: see text] results in a deshielding of 404 ppm. 77Se chemical shifts were found to be in the range −240 to −270 ppm (relative to (CH3)2Se) for selenolates, approximately −80 ppm for selenols, 230–360 ppm for diselenides, and 250–340 ppm for selenenyl sulfides. The 77Se chemical shift is also affected by titration of neighboring carboxylic acid and ammonium groups, and their pkA values can be calculated from 77Se chemical shift data.

1H and 19F nuclear magnetic resonance spectra of the adduct BF3.H2O

1967 ◽  
Vol 45 (8) ◽  
pp. 859-863 ◽  
Author(s):  
R. J. Gillespie ◽  
J. S. Hartman
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperatures ◽  
Boron Trifluoride ◽  
Proton Exchange ◽  
Rapid Proton ◽  
Rapid Proton Exchange ◽  
Nuclear Magnetic Resonance Spectra ◽  
Donor Acceptor ◽  
Nuclear Magnetic

It is shown by low-temperature 1H and 19F nuclear magnetic resonance (n.m.r.) spectroscopy that boron trifluoride monohydrate is formed in dilute solutions in acetone containing both water and BF3. In solutions in which [H2O] < [BF3], proton–fluorine coupling is observed which definitely establishes that in acetone solution at low temperatures the monohydrate is the simple donor–acceptor complex H2O → BF3. In solutions in which [H2O] > [BF3], no proton–fluorine coupling was observed because of rapid proton exchange.

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