Exchange Broadening of Spin–spin Triplets in Nuclear Magnetic Resonance Spectra. Application to the System Ethanol–water

Paterson, William G.

doi:10.1139/v63-101

Cited by 12 publications

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References 20 publications

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“…The specific rate constant, k, for reaction [l] was calculated from the relation (1,3) where zR0, is the mean lifetime of a hydroxyl proton on a 2-propanol molecule ROH before exchange with a proton on a water molecule.…”

Section: Resultsmentioning

confidence: 99%

Nuclear magnetic resonance study of proton exchange in the water – 2-propanol system

Tewari¹,

Li²

1970

Can. J. Chem.

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Nuclear magnetic resonance (n.m.r.) measurements on proton-exchange kinetics in aliphatic alcohol -water solutions have been reported by several authors (1-5). The protolysis reaction is found to be both acid and base catalyzed. Recently, Fukumi et al. (5) have reported specific rate constants for different processes in the water-2-propanol system. They calculated a value of 2.0 1 mole-' s-' at 28 "C for the rate constant, k, of proton exchange between 2-propanol and water with no externally added acid or base 111 ROH + *HOH + ROH* + HOH where R = i-C,H,. This value is to be compared with Ic = 0.35 f 0.06 1 mole-' s-I at 42O, reported by Paterson (3b). In view of the wide disagreement, we report here the specific rate constants for reaction [I], determined at four different temperatures, as well as the energy of activation. In addition, the effects of the presence of several electron donors on the kinetics of reaction [ I ] are reported. Experimental MaterialsAll reagents used were Fisher reagent grade, dried and doubly distilled by the usual methods. De-ionized, doubly distilled water was prepared; its p H varied between 6.7 and 7.0. The alcohol-water solutions were prepared by weight and the concentrations in moles/l calculated from the known density data at various temperatures (6). Since the solutions slowly leach impurities from the glass (3), a given set of n.m.r. measurements were done on the same day that the materials were distilled. Nuclear Magnetic Resonance MeasurementsSpectra were obtained with a Varian A-60 spectrometer. Care was taken to keep the radiofrequency power level well below saturation and the field homogeneity such that a resolution of 0.3 Hz or better was attained. During the recording of the spectra the temperature remained constant to -I lo. The precision in the n.m.r. measurements varied from 0.02 to 0.05 Hz, depending on signal shape. All measurements were an average of at least six determinations. Results and DiscussionIn neat 2-propanol at 31°, the -OH signal was a sharp doublet with spacing 4.22 Hz. In the alcohol-water solutions used in the present study, the -OH signals in 2-propanol and water are quite well separated; thus at 31°, for [H20] = 7.2 M, [2-propanol] = 11.2 M, the two -OH signals are separated by 44.6 Hz. The linewidth of the water signal, however, could not be measured accurately because of interference from the methine proton signal, and this has also been reported by Paterson (3b).The specific rate constant, k, for reaction [l] was calculated from the relation (1, 3) where zR0, is the mean lifetime of a hydroxyl proton on a 2-propanol molecule ROH before exchange with a proton on a water molecule.In order to evaluate successfully the mean lifetimes, it is necessary to know two experimentally determinable parameters: ( I ) the transverse relaxation time, T2, in the absence of exchange and (2) the peak separation of the O H doublet in neat 2-propanol, which is due to spin-spin interaction, Sm. Transverse relaxation time, T2, was considered to be governed chiefly b...

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Section: Resultsmentioning

confidence: 99%

Nuclear magnetic resonance study of proton exchange in the water – 2-propanol system

Tewari¹,

Li²

1970

Can. J. Chem.

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Hydroxide‐alkoxide ion equilibria and their influence on chemical reactions

Murto

1971

The Hydroxyl Group (1971)

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NMR Study of the ROH‐D₂O Systems I. Ethanol, Propanol‐1, Propanol‐2

Cernicki¹

1965

Ber Bunsenges Phys Chem

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The NMR spectra of mixtures of ethanol, propanol-1, and propanol-2 with heavy water are discussed. The intensities of the hydroxyl and water signals have been found to agree with the theoretical probability curves. No coalescence of these signals could be found up to molar fraction of D,O equal to 0.9. The spectra of ROH-D,O systems are shown to be more representative of water-alcohol mixtures than are those of ROH-H,O systems. Die KMR-Spektren von Mischungen von Xthanol, Propanol-1 und Propanol-2 mit schwerem Wasser werden diskutiert. Es wird gefunden, daB die Intensitaten der Hydroxyl-und der Wassersignale mit den theoretisch zu erwartenden Hiufigkeiten im Einklang stehen. Bis zu D,O-Molenbriichen von 0,9 fallen diese Signale nicht zusammen. Es wird gezeigt, da13 die Spektren der ROH-D,O-Systeme mehr AufschluB uber Wasser-Alkohol-Mischungen geben als die der ROH-H,O-Systeme. Introdrrction Addition of small amounts of acid or base to ethanol increases the rate of exchange of hydroxyl protons, i. e. of the reaction + EtOH &OH + EtOir which decouples them from methylene protons and, as a consequence, simplifies the NMR spectrum of the alcohol [8]. This phenomenon can be examined quantitatively by using McConnell's treatment [9] of the Bloch equations [14]; the values of the mean life-time between exchange events has been estimated by advanced approach [1, lo]. The same results have been obtained by adding buffers to EtOH [4].The addition of an inert solvent, on the other hand, decreases the degree of association of ethanol molecules and causes a shift of the OH signal into a higher field [2, 31. The influence of heat combines these two effects[13] since the increase of temperature favours both the proton exchange and dissociation. These results can be applied also to other simple alcohols [2, 5, 81.Water, when added to ethanol, acts in the same wayboth as an exchange accelerator and a diluent. Its accelerating action is based on reactionEtOA + HOH F? EtOH + HOk.Here, in addition, the coalescence of OH and H,O signals has been found at about 50 mole-% H,O when its concentration is varied from 0 to 100% [17]. The same phenomenon has been observed when acid has been added [6] or temperature increased 1151 in a water-ethanol mixture, indicating the increase of the rate of exchange of hydroxyl protons. These investigations have also been extended to other simple alcohols [8, 11, 121. So far, all papers deal with mixtures of alcohols and ordinary water. The strong H,O signal, however, makes the observation of alcohol signals difficult, particularly in samples with high water concentration. We have, therefore, determined to examine the NMR spectra of mixtures of heavy water and simple alcohols. The latter have included ethanol, propanol-1, and propanol-2. Methanol has been omitted from this series owing to its extreme rate of exchange [8] which makes it susceptible to the least amount of impurities. A qualitative treatment of such systems is given in this paper. ExperimentalHeavy water used was that of the Isotopes Spe...

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Exchange Broadening of Spin–spin Triplets in Nuclear Magnetic Resonance Spectra. Application to the System Ethanol–water

Cited by 12 publications

References 20 publications

Nuclear magnetic resonance study of proton exchange in the water – 2-propanol system

Nuclear magnetic resonance study of proton exchange in the water – 2-propanol system

Hydroxide‐alkoxide ion equilibria and their influence on chemical reactions

NMR Study of the ROH‐D₂O Systems I. Ethanol, Propanol‐1, Propanol‐2

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Exchange Broadening of Spin–spin Triplets in Nuclear Magnetic Resonance Spectra. Application to the System Ethanol–water

Cited by 12 publications

References 20 publications

Nuclear magnetic resonance study of proton exchange in the water – 2-propanol system

Nuclear magnetic resonance study of proton exchange in the water – 2-propanol system

Hydroxide‐alkoxide ion equilibria and their influence on chemical reactions

NMR Study of the ROH‐D2O Systems I. Ethanol, Propanol‐1, Propanol‐2

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NMR Study of the ROH‐D₂O Systems I. Ethanol, Propanol‐1, Propanol‐2