Reactions thermodynamic control

Example 7.5. Reversible competing reactions kinetic and thermodynamic reaction control [4]... 

One can add reverse reactions to the parallel reaction model to illustrate what chemists refer to as kinetic and thermodynamic reaction control. Often a reactant A can form two (or more) products, one of which (B) is formed rapidly (the kinetic product) and another (C) which forms more slowly (the thermodynamic... 

Figure 7.7. Plot of the numbers of A, B, and C ingredients illustrating kinetic and thermodynamic reaction control as described in Example 7.5...

Figure 24 Illustration of kinetic and thermodynamic reaction control B is the kinetically favored product (higher probability of formation from A), and C is the thermodynamically favored product (greater equilibrium constant with A).

The anomeric oxygen activations described above could not fulfill the requirements put forward. Either they failed to provide both activated intermediates or both anomeric glycosides were not obtained. Obviously, for a stereocontrolled activation of the anomeric oxygen, the anomerisation of the 1-OH, or the 1-0", group in the presence of base has to be taken into account (Scheme 16). Thus, in a reversible activation process and with the help of kinetic and thermodynamic reaction control both activated anom-ers should eventually be obtainable. 

NaH, both anomers can be isolated in pure form and high yield via kinetic and thermodynamic reaction control. Both anomers are thermally stable and can be stored easily. 

In a multiple addition of ethyl bromide to benzene ortho and para substitution is expected after the first monosubstitution step because an alkyl group is an activating group. The actual reaction product is 1,3,5-triethylbenzene with all alkyl groups as a meta substituent. Thermodynamic reaction control makes sure that thermodynamically favored meta substitution with steric hindrance minimized takes prevalence over less favorable ortho and para substitution by chemical equilibration. 

The Meerwein-Ponndorf Verley reduction of 3-methyl-4-ehromanone (5) provides another illustrative example of kinetic versus thermodynamic reaction control. Continuous removal of the acetone formed (kinetic control) gives mainly the nx-alcohol 6 [d.r. (cisjtram) 73 27] boiling under reflux affords an inverse mixture [d.r. (cis/trans) 37 63]199. 

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