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Reversible Intermolecular Chemical Processes

Note how this particular bond reorganization of two n bonds and one cyclopropane bond interconverts three pairs of hydrogens (and the attached carbons) H with H,., Hj- with He , and Hj- with Hj. Repetition of this rearrangement with other sets of 7t and cyclopropane bonds ultimately renders all 10 hydrogens (and carbons) equivalent. [Pg.164]

Many examples of this type of fluxional behavior are now known. But had it not been for NMR, most would never have been discovered  [Pg.164]

From the signal integrations it is clear that the enol form constitutes 86% of the equilibrium mixture. Furthermore, at room temperature the rate of equilibration must be much slower than the NMR time scale to observe both sets of sharp signals.  [Pg.165]


The actual adsorption of vapor molecules takes place mainly on the surface of internal passages within the adsorbent particles, since that is where most of the available surface exists. The adsorption process may be either physical or chemical in nature. Physical adsorption is a readily reversible process that occurs as a result of the physical attraction between the gas molecules and the molecules of the solid surface. If the gas-solid intermolecular attraction is greater than the intermolecular attractions in the gas phase, the gas will condense on the solid surface, even though its pressure is lower than its vapor pressure at the prevailing temperature. For example, the equilibrium adsorption pressure of acetone on activated carbon may, under some conditions, be as little as 150 to 1,100 of the equilibrium vapor pressure at... [Pg.241]

To answer this question, information obtained from studies of irreversible systems needs to be examined. Irreversible protein processes may occur as a result of intermolecular interactions (i.e., aggregation, chemical modification, intermolecular cross-linking). Although an attempt is generally made to search for conditions that provide maximal reversibility, perhaps by altering the solution conditions (i.e., pH, salt content, lowering the protein concentration) that minimize contact and electrostatic interactions, many systems can still exhibit little or no reversibility. This would be the case for the core protein obtained by limited... [Pg.330]

These processes that bring about averaging of spectral features occur reversibly, whether by acid-catalyzed intermolecular exchange or by unimolecular reorganization. NMR is one of the few methods for examining the effects of reaction rates when a system is at equilibrium. Most other kinetic methods require that one substance be transformed irreversibly into another. The dynamic effects of the averaging of chemical shifts or coupling constants provide a nearly unique window into processes that occur on the order of a few times per second. (The subject is examined further in Section 5-2.)... [Pg.25]

Although intermolecular photocycloaddition of two benzene rings in the condensed phase has not been observed, this reaction is common for polycyclic aromatic hydrocar-bons. For example, anthracene-9-carbonitrile (231) in acetonitrile undergoes efficient [4 + 4] photocycloaddition with anthracene to give an adduct 232 in 94% chemical yield (Scheme 6.90).833 This process is thermally reversible. [Pg.286]

Unimolecular reactions with thermal, optical, or chemical activation are governed by a competition between intramolecular isomerization, dissociation, or the reverse association (or recombination) processes, and intermolecular energy transfer in collisions. In addition to these traditional unimolecular reactions, many other reaction systems may be considered from a unimolecular point of view when a particular intramolecular event can be separated from preceding or other subsequent processes. Following this more general use of the term, unimolecular reaction rate theory has found a quite general application, and has been harmonized with other theories of reaction dynamics. [Pg.175]


See other pages where Reversible Intermolecular Chemical Processes is mentioned: [Pg.164]    [Pg.164]    [Pg.164]    [Pg.164]    [Pg.164]    [Pg.164]    [Pg.33]    [Pg.5]    [Pg.66]    [Pg.218]    [Pg.191]    [Pg.331]    [Pg.194]    [Pg.8]    [Pg.166]    [Pg.759]    [Pg.77]    [Pg.464]    [Pg.110]    [Pg.164]    [Pg.66]    [Pg.27]    [Pg.610]    [Pg.628]    [Pg.294]    [Pg.109]    [Pg.139]    [Pg.185]    [Pg.361]    [Pg.22]    [Pg.204]    [Pg.193]    [Pg.595]    [Pg.86]    [Pg.93]    [Pg.1256]    [Pg.305]    [Pg.101]    [Pg.251]    [Pg.308]    [Pg.356]    [Pg.312]    [Pg.522]    [Pg.88]    [Pg.599]   


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Chemical reverse

Chemical reversibility

Chemically reversible

Intermolecular processes

Process reverse

Reversal processing

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