Intramolecular hydrogen exchange

Scheme 3. Isomerization and intermolecular and intramolecular hydrogen exchange reactions of I-butene.

Some NMR data of the above complexes are worth mentioning. It is interesting for the general discussion of bonding in these n complexes that in the 13C-NMR spectrum of cyclopentadienylberyllium bromide (XXIc) a 13C—9Be coupling has been observed (53). Rapid intramolecular hydrogen exchange takes place in the borate units of the compounds XXIf and g (75,77). 

The intramolecular hydrogen exchange that occurs during fragmentation of 3-dimethylamino-steroids in the mass spectrometer has been studied.9 The chemistry of uiose Buxus alkaloids which are based on the 19-nor-B-homopregna-9a(10),9(ll)-diene nucleus has been reviewed.10... 

This model has been used for the description of Arrhenius curves of H-transfers as described in more detail in Chapter 6. The next two chapters show applications of these symmetry effects. First the para-hydrogen induced polarization (PHIP) experiments are discussed. There the symmetry induced nuclear spin polarization creates very unconventional NMR lineshape patterns, which are of high diagnostic value for catalytic studies. Then in Section 21.4 symmetry effects on NMR line-shapes and relaxation data of intramolecular hydrogen exchange reactions are discussed and examples from iH-liquid state and H-solid state NMR are presented and compared to INS spectra. The last section gives an outlook on possible future developments in the field. 

The above cis effect is significant because of its apparent role as the nascent interaction in intramolecular hydrogen exchange processes. The intermediate is... 

ISOTOPIC EXCHANGE AND OTHER INTRAMOLECULAR HYDROGEN EXCHANGE REACTIONS... 

The keto-enol tautomeric equilibrium of acetylacetone is an intramolecular hydrogen exchange process. High-pressure NMR was used to study changes in this equilibrium over a pressure range to 2.5 kbar and temperatures to 145 C (51). With an increase in temperature at constant pressure, the equilibrium distribution shifted to the keto tautomer. An increase in pressure did not change the keto-enol distribution at any temperature. From the high-pressure experiments as a function of temperature the reaction enthalpy, A/J, and entropy, AS, were determined to be 2.80 0.02 kcal/mol and 7.2 0.3 cal/K mol, respectively. 

Titanium, Zirconium, and Hafnium - The dynamics of intramolecular hydrogen exchange in cyclic organohydroborate zirconocene complexes have been investigated by and NMR spectroscopy.The NMR spectra of... 

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