Carbon-carbon bond formations and functional group transformations are the most fundamental reactions for the construction of molecular frameworks and are at the forefront of organic chemistry research. The Morita-Baylis-Hillman MBH type reactions possess the two most important requirements - atom economy and generation of multi-functional groups.
The last decade has seen exponential growth of the MBH reaction and its applications.
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In fact, it is already one of the most powerful carbon-carbon bond-forming methods widely used in organic synthesis. Since the s, more and more research groups have initiated work on different aspects of the MBH reaction. These have focused on the scope of the substrates, novel catalysts especially chiral catalysts , reaction mechanisms, and synthetic applications. Consequently, there is now a need for a reference detailing the chemistry of this important reaction.
Metal substitution modulates the reactivity and extends the reaction scope of myoglobin carbene transfer catalysts. Stereoselective olefin cyclopropanation under aerobic conditions with an artificial enzyme incorporating an iron-chlorin e6 cofactor. ACS Catal. Oohora, K. Catalytic cyclopropanation by myoglobin reconstituted with iron porphycene: acceleration of catalysis due to rapid formation of the carbene species. Liu, C. Adding new chemistries to the genetic code. Lewis, J. Metallopeptide catalysts and artificial metalloenzymes containing unnatural amino acids. Pott, M. A non-canonical proximal heme ligand affords an efficient peroxidase in a globin fold.
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Jentzen, W. Conservation of the conformation of the porphyrin macrocycle in hemoproteins. Renata, H. Identification of mechanism-based inactivation in Pcatalyzed cyclopropanation facilitates engineering of improved enzymes. Callot, H. Rearrangement of N-substituted porphyrins. Preparation and structure of homoporphyrins. Khade, R. Catalytic and biocatalytic iron porphyrin carbene formation: effects of binding mode, carbene substituent, porphyrin substituent, and protein axial ligand. Dzik, W. This can occur by increasing the entropy of the system, often through the formation of gaseous reaction products, which have high entropy.
Since the entropy increases with temperature, many endothermic reactions preferably take place at high temperatures. On the contrary, many exothermic reactions such as crystallization occur at low temperatures. Changes in temperature can sometimes reverse the sign of the enthalpy of a reaction, as for the carbon monoxide reduction of molybdenum dioxide :.
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This reaction to form carbon dioxide and molybdenum is endothermic at low temperatures, becoming less so with increasing temperature. Changes in temperature can also reverse the direction tendency of a reaction. For example, the water gas shift reaction. Reactions can also be characterized by the internal energy which takes into account changes in the entropy, volume and chemical potential.
The latter depends, among other things, on the activities of the involved substances. The speed at which reactions takes place is studied by reaction kinetics. The rate depends on various parameters, such as:. Several theories allow calculating the reaction rates at the molecular level.
This field is referred to as reaction dynamics. The rate v of a first-order reaction , which could be disintegration of a substance A, is given by:. The rate of a first-order reaction depends only on the concentration and the properties of the involved substance, and the reaction itself can be described with the characteristic half-life. More than one time constant is needed when describing reactions of higher order. The temperature dependence of the rate constant usually follows the Arrhenius equation :. One of the simplest models of reaction rate is the collision theory.
More realistic models are tailored to a specific problem and include the transition state theory , the calculation of the potential energy surface , the Marcus theory and the Rice—Ramsperger—Kassel—Marcus RRKM theory. In a synthesis reaction, two or more simple substances combine to form a more complex substance. These reactions are in the general form:.
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