Intermolecular proton exchange, rate

Indirect Exchange Rates. In this case, the line shape is indirectly related to the acid-base equilibrium. Besides measuring intermolecular processes like the proton exchange rates, DNMR often has been used to measure intramolecular processes like conformational changes that occur on the same time scale. When the activation energy of such a process is very different in the acidic and basic forms for an indicator, DNMR can be used to measure the ionization ratio. 

Addition of SbFj makes the reaction too slow to measure and band broadening of the solvent peak increases with temperature. Therefore they concluded, in contrast to MacLean and Mackor, that intermolecular proton exchange with solvent (acid) is the main process causing the degeneracy of [289]. The value of 3 obtained was 13.7 — 15.5 kcal moh, depending upon the hydrocarbon concentration. The lower basicity of the solvent medium was proposed to explain the much lower reaction rate in FSO3H as compared with HF-BF3. 

The spectra of intramolecularly hydrogen bonded enol systems continue to receive attention. In the case of )3-diketones and o-hydroxy-aromatic aldehydes and ketones, the width of the enolic proton peak is inversely related to the rate of intermolecular proton exchange. ... 

In a thorough study of several compounds of type 5 with R4 = Me, Kozerski and coworkers2 8 followed the rate of C=C rotation simultaneously with the rate of intermolecular N-proton exchange and found very similar barriers (ca 20kcalmol 1) for the two processes. This was interpreted as a catalyzed E-Z exchange proceeding by... 

Coupling of amine protons with vicinal H atoms is usually not seen in aliphatic amines because of their rapid intermolecular exchange. However, for -NH-CH moieties (enamines, aromatic amines, amides, etc.), the exchange rate is slower and splitting is often observed. The H-C-N-H coupling depends on the conformation in a similar way as the H-C-C-H coupling (see Chapter 5.1). For N-CH3 and N-CH2 groups Jhcnh ... 

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